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2023 | Buch

International RILEM Conference on Synergising Expertise towards Sustainability and Robustness of Cement-based Materials and Concrete Structures

SynerCrete’23 - Volume 2

herausgegeben von: Agnieszka Jędrzejewska, Fragkoulis Kanavaris, Miguel Azenha, Farid Benboudjema, Dirk Schlicke

Verlag: Springer Nature Switzerland

Buchreihe : RILEM Bookseries


Über dieses Buch

This book highlights the latest advances, innovations, and applications in cement-based materials (CBM) and concrete structures, as presented by leading international researchers and engineers at the International RILEM Conference on synergizing expertise toward sustainability and robustness of CBM and concrete structures (SynerCrete), held in Milos Island, Greece, on June 14-16, 2023. The aim of the conference was to discuss and arouse progress in research, development, and application of CBM and structural concrete through combination of expertise from distinct fields of knowledge, such as performance-based design, 3D modeling for analysis/design, building information modeling, and even robotics, while keeping focus on multiscale approaches at time and spatial levels. It covers a diverse range of topics concerning alternative concrete formulations for adaptation to climate change, performance-based and multiphysics/multiscale design and innovative testing, structural health monitoring and maintenance management, integral BIM-based planning, and resource-responsible building. The contributions, which were selected by means of a rigorous international peer-review process, present a wealth of exciting ideas that will open novel research directions and foster new multidisciplinary collaborations. The two volumes encompass more than 200 original contributions in the field.



Supplementary Cementitious Materials

Harvest Residues Ash and Ceramic Powder as Pozzolanic Materials for Developing Sustainable Building Materials

As the global population increases, a large amount of solid waste generates along, occupying large landfill sites for its disposal. Conversion of this waste into other alternative resources will reduce the load on non-renewable building materials and help in solving the landfilling problem. Incorporating mainstream wastes, such as: fly ash, blast furnace slag, rice husk ash, recycled aggregate and bricks in mortar or concrete has become one of the green ways to deal with waste from the agriculture and industry. Maintaining sustainability at the centre of this paper, two types of waste materials have been selected for the study. First is ceramic waste powder obtained from broken or distorted ceramic waste products, and the second is harvest residues ash from the agricultural biomass combustion. The present study aims at evaluating basic chemical, physical and pozzolanic properties of collected cement-alternative materials - phase 1 and testing mechanical and durability properties of concrete (compressive strength, water impermeability and wear resistance) produced with high share of these wastes. The results indicate that optimal types of industrial and agricultural waste materials can be effectively used in the concrete industry as cement substitutes up to the 50% replacement level, while maintaining satisfying concrete’s performance and meeting the principles of sustainable development.

Slobodan Šupić, Vlastimir Radonjanin, Mirjana Malešev, Ivan Lukić, Vladan Pantić
Chemical and Mechanical Characterization of a Novel CSA Blended Cement Based on CDW Inorganic Fractions

Cement is a construction material widely used to improve the socio-economic development of a society. However, for its production path, it needs significant amounts of raw materials (limestone, clay, bauxite, etc.), which is currently outside the Environmental Policies. For this reason, any alternative to manufacture sustainable eco-cement based on the circularity of industrial waste is a priority line for the cement sector. This work presents the characterisation results of a calcium sulfoaluminate cement clinkerized (CSA-L), in a laboratory muffle at 1250ºC for 60 min, by partial replacement of raw materials by different construction and demolitions wastes (CDW) from the fine fraction of concrete (<5 mm), deconstruction building laminated glass and recycled gypsum. Subsequently, its physical-mechanical behaviour (water demand, setting times, soundness, mechanical properties and microporosity) was analysed in an eco-blended cement made by combining 90% OPC and 10% CSA (commercial and clinkerized ones), as preliminary studies for the manufacture of eco-cement materials for 3D printing. The results obtained demonstrate the feasibility of using CDW as secondary raw materials for the formation of a CSA eco-cement, with a mineralogical composition consisting of 24% Ye’elimite (C4A3$), 6% Larnite (α-C2S) and 31% Brediggite (Ca7Mg(SiO4)4. This eco-CSA-L cement shows an enriched nature in Brediggite with respect to commercial CSA-C cement. The binary mixture of cements (OPC + 10% CSA-L) shows a rheological and mechanical behaviour close to the reference OPC.

Moisés Frías, Sagrario Martínez-Ramírez, Lucía Fernández-Carrasco, Rosario García Giménez, Raquel Vigil de la Villa, Manuel Monasterio, Jaime Moreno-Juez, Iñigo J. Vegas-Ramiro
Study on Properties and Performance of Green Concrete

Conventional concrete (CC) is for decades the most used construction material worldwide thanks to its good properties such as high strength, high thermal mass, low noise transmission, and high fire resistance. Cement is an important component of CC. The cement industry is a significant source of emissions and accounts for roughly 8% of the world’s CO2 emissions today, which means all improvements that can be made within this single industry benefit the emissions reduction goals. Green concrete (GC) is the development in the field of construction technology, which offers a more sustainable and eco-friendly solution as a building material. GC deals with the mentioned negative issue of cement, since it offers new cementitious matrices where some part of the Portland cement of CC is being replaced by some supplementary cementitious materials, such as industrial by-products, agricultural wastes, or municipal wastes. This paper studies the properties, structural performance, and environmental benefits of GCs. The investigation is done through a literature review, identifying the knowledge gaps, and providing suggestions for further research. The results indicate that there is a good potential to significantly reduce the climate impact of CC by using alternative binder materials in GC.

Lisen Johansson, Alireza Bahrami, Mathias Cehlin, Marita Wallhagen
Optimizing the Flexural Strength of Cement Mortar Incorporating Natural Pozzolan Using Taguchi Method

Partially replacing cement with supplementary cementitious materials (SCMs) has been extensively studied in the past. Despite the ability of SCMs to alleviate the environmental concerns of cement, the mechanical properties of cement mortars incorporating SCMs are affected by such modifications to mix design. Flexural strength is essential for cement mortar applications, such as repair and retrofitting. In this study, the Taguchi method was used to optimize the mixture proportions of cement mortar incorporating natural pozzolan (NP) as an SCM for superior flexural strength. The factors and their corresponding levels considered in this investigation included the binder content at 350, 400, 450, and 500 kg/m3, water-to-binder (w/b) ratio at 0.450, 0.475, 0.500, and 0.525, dune sand percentage replacement of natural sand at 5, 10, 15, and 20%, NP percentage replacement of cement at 5, 10, 20, and 40%, and high range water reducer (HRWR) dosage at 0.25, 0.50, 0.75, and 1.00%. The response criterion was the 28-day flexural strength. Sixteen mixes were cast, cured for 28 days in water, and tested for flexural strength. The optimum mortar mix had a binder content of 500 kg/m3, a water-to-binder ratio of 0.500, a dune sand content of 20%, a natural pozzolan content of 40%, and high range water reducer of 1% by binder mass. Its 28-day flexural strength response was 7.2 MPa. The study highlights the possibility of creating cement mortar mixes having high flexural strength for construction applications while substituting 40% of the cement with NP.

Jad Bawab, Hilal El-Hassan, Amr El-Dieb, Jamal Khatib
Influence of Aggregate Type on the Properties on SCC with Fly Ash

This study compared the performance of self-compacting concrete (SCC) based on fly ash addition and limestone filler. A SCC prepared with Portland cement, river sand, and limestone filler was used as a reference sample. Additional experimental self-compacting concretes with different types of fine aggregates, fillers, and special additives for increasing freeze-thaw resistance were prepared and optimized. The correlation between mix design, i.e., percentage of barite sand and additives, and properties of fresh SCC (slump-flow test, V-funnel test, and L-box test), as well as properties of hardened SCC (compressive strengths), were investigated and discussed.

Ksenija Janković, Marko Stojanović, Dragan Bojović, Anja Terzić, Srboljub Stanković
R3-Test for Pozzolanic Reactivity: Experimental Issues and Practical Recommendations for Hydration Stoppage with Isopropanol

In recent years, the global need on alternative binders for the construction industry has driven the development of novel testing methods for evaluating the reactivity of supplementary cementitious materials (SCMs). One method that has attracted particular attention is the so-called R3-test, that measures the reactivity of SCMs while eliminating the influence of cement. The evaluation of hydration reaction products with time can be done by using micro analysis techniques, where a stopping procedure for the hydration process and drying the samples would be necessary. One possible method to achieve this is the solvent exchange method with isopropanol, which is also recommended for stopping the hydration of cement paste samples. However, applying the same procedure to clinker-free R3-samples may cause various problems that directly influence the measured data. Therefore, this study addresses experimental issues related to the reproducibility of results when hydration was stopped with isopropanol, due to the sample heterogeneity as well as the content of free water and remaining isopropanol. Emphasis is on R3-testing of different types of metakaolin and the examined data was determined from thermogravimetric analysis. The hydration stoppage procedure was adjusted with respect to the identified issues and practical recommendations are provided as: 1) grinding the whole sample (10 g) together with 10 mL isopropanol; 2) taking an aliquot of 3 g from the sample and placing it in 50 mL isopropanol followed by the drying procedure for cement paste samples; 3) drying the sample in a desiccator for at least 12 h (<2d); 4) hand-milling just before testing .

Kira Weise, Neven Ukrainczyk, Luca Marei Endell, Eduardus Koenders
Reduction of CO2 Emission by Using Low Carbon Concretes with Accelerating Admixtures

A major part of the CO2 emitted by the concrete industry comes from the production of cement clinker and covers 5–8% of the world’s CO2 emissions. As the development of long-term solutions for CO2 reduction may take several decades, the need of immediate actions is required. One possible solution can be the replacement of the cement clinker with the ground granulated blast furnace slag. However, due to the high level of slag in low carbon concretes the setting time and early-strength of the concrete can be decreased. Therefore, it is important to ensure a reasonable early-strength development of low carbon concretes for application in the construction industry.This study aims to investigate the effect of several accelerating admixtures to boost the early-strength development of low carbon concretes. The amount of each accelerating admixture required to enhance the hydration rate of CEM III/A and CEM III/B cements to the levels of CEM II/B cement was determined based on the heat development curves. The defined amount of each accelerating admixture was used to cast concrete samples and determine their compressive strength at the early (15, 24, 39, and 48 h) and later (7, 28, and 91 days) stages of hardening. The compressive strength of the low carbon concretes was evaluated with the ultrasound pulse velocity, rebound hammer, and standardised compressive strength tests.

Ekaterina Illarionova, Anna Antonova, Fahim Al-Neshawy, Jouni Punkki
The Effect of Ladle Furnace Slag (LFS) Content Replacement as a Supplementary Cementitious Material in Portland Cement-Based Systems

Portland cement (OPC) and steelmaking industries exhibit high production levels and are expected to continue in the near future. Their industrial processes are not considered environmentally friendly and are estimated to be responsible for 4–7% of worldwide CO2 emissions. To mitigate their negative externalities, they introduce several improvements in their processes. The steelmaking industry generates a large volume of solid waste, mainly slags. Electric arc furnace slag (EAFS) and ladle furnace slag (LFS) shows exciting properties to be used as construction material. Currently, only EAFS is valorized, mainly as a granular material for different pavement layers. Instead, LFS presents technological barriers (low cementing activity and expansive problems) that prevent them from being valorized and finally deposited in landfills. This work explores a safe/high-value application for LFS as a supplementary cementitious material (SCM). Pastes/mortars were produced to study the effect of varying the LFS-content replacement. Chemical/mineralogical characterization of raw/hydrated samples and fresh/hardened state properties were tested at different ages to study the physical-mechanical performance and microstructure evolution. Our results suggest that LFS has good potential as SCM, modifying the fresh/hardened performance depending on LFS content: by decreasing workability, accelerating the setting time, and lowering the strength. Also, it increases the potential volumetric instability issues. The compressive strength gap decreases with time, reaching over 30 MPa for 25/50 wt% replacements at 28–98 days. Finally, the microstructure evolution shows a shift in the typical OPC hydration reactions, producing higher AFm-AFt products due to the higher calcium-aluminates reactive phases in the slag.

Paulo Araos, Anna Uribarri, Marilda Barra, Diego Aponte
Micromechanical Properties Assessment of Slag Blended Cements Using Nanoindentation and Scanning Electron Microscopy

Sustainability concerns related to the CO2 emissions of Portland cement production led to the exploitation of some by-products as replacement materials, such as slag. This requires a good understanding of the blended cementitious materials at the microscale to fully explain the observed behavior of the structures at the macroscale. The nanoindentation technique was used to assess the effect of slag incorporation on the micromechanical properties at the early age through the study of four cement pastes with different replacement ratios. Then, the nanoindents were observed using scanning electron microscopy to address the issues related to nanoindentation data deconvolution. The results show that the hydration products are intimately intermixed and that the boundary condition of indented areas must be considered when assessing the properties of individual phases to reduce the measurement variability. In addition, the incorporation of slag was found to cause a decrease in hydration products’ elastic modulus and creep properties due to the gel porosity increase.

Imane Bekrine, Benoît Hilloulin, Ahmed Loukili
Characterizing Sewage Sludge Ashes in Dry and Wet States for Use as SCM

The increasing production of sewage sludge, a residue from wastewater treatment, has led to the need for disposal methods that reduce environmental impact. The calcination of this mud residue produces the sewage sludge ashes (SSA), a powdery by-product with valuable characteristics that can serve as a secondary material source. This study explores the feasibility of incorporating SSA, as a partial substitution for Ordinary Portland Clinker, in cement-based materials. The chemical, mineralogical and physical properties of SSA were characterized to understand its impact on the cement matrix. Following that, cement paste samples and mortars were prepared with substitution rates of 0, 10, 20, 30%, and 25% respectively. The results of the work show that SSA has a possible porosity, resulted in an increase in the water demand after SSA incorporation. In addition, SSA was found to contain heavy metals, phosphorus, sulfate and lime which affects the cement hydration reaction. The modified SSA-cement pastes showed a delay in the early hydration period. A long-term positive effect on mechanical properties of mortars was noticed, with a Strength Index Activity of 86% at 28 days. The results obtained in this study encourages the use of SSA in cement-based materials in cement-composites.

Danah Shehadeh, Alexandre Govin, Philippe Grosseau, Hichem Krour, Laetitia Bessette, Gonzague Zeigler
Properties of Belite-Rich Cement with Supplementary Cementitious Materials

The article deals with the role of supplementary cementitious materials (SCMs) on the properties of laboratory belite-rich cements prepared from low-energy clinker doped with SO3. The low lime saturation factor (LSF) clinker with belite as the main phase was synthesized at 1350 °C using industrial raw materials. Alite/belite ratio is opposite to that of ordinary Portland cement (OPC). ß-C2S and M1 alite are the main modifications in doped clinkers. Cements were prepared by grinding clinkers to 400 m2/kg fineness in a laboratory ball mill. Replacement of 10, 20 and 30 wt.% of calcined clay, ground limestone, blast-furnace slag, ground glass and 5, 10 and 15 wt.% of silica fume were tested. Along with clinker properties, early properties of cement pastes and mortars were studied by isothermal calorimetry. Strength development of mortars were monitored after 2, 7, 28 and 90 days. Heat flow development during early hydration is strongly affected by SCMs, as seen in the position and intensities of aluminate, silicate, second aluminate and ettringite to monosulfate (AFt-AFm) conversion peaks. Despite low alite content, the cements have decent early and good long-term strengths, even at higher replacement levels. Binary combinations of OPC with calcined clay, blast-furnace slag or ground grass gave the best results. The introduction of such cements would significantly decrease the CO2 emissions and energy demand and partly save the primary sources of limestone.

Martin Boháč, Dana Kubátová, Anežka Zezulová, Theodor Staněk
Development of Eco-cement from Recycled Low-Carbon Footprint By-product

For several decades, the cement industry has been actively seeking alternative raw materials to reduce greenhouse gas emissions and energy consumption. In pursuit of partial replacements for clinker, worldwide research has focused primarily on industrial (fly ash, Si-Mn slag, fired clay-based) and agroforestry (rice husk, sugar cane) waste. The common denominator in all such waste, its pozzolanicity, determines mechanical performance and durability throughout the service life of the cement produced. In this study, two types of industrial waste (construction and demolition waste and biomass waste) were added separately or jointly in different proportions to Portland clinker to ascertain the effect on the rheological, physical and mechanical properties of the resulting binary and ternary eco cements. The use of biomass waste and the joint addition of both kind of wastes were observed to yield cements in which the fresh and hardened properties of the new eco-cement were not significantly lower than in conventional binders and these binders could be apt to use in the manufacture of cement-based material (mortar or concrete) with low-carbon footprint .

Paula Velardo, Marta Barroso, Isabel F. Sáez del Bosque, María I. Sánchez de Rojas, Nele De Belie, César Medina Martínez
Recycling Potential of Cellular Lightweight Concrete Insulation as Supplementary Cementitious Material

Buildings are responsible for 40% of the total energy consumption annually in Europe, along with the respective greenhouse gas emissions. To mitigate these impacts, intensive research is ongoing in the sector of Nearly Zero-Energy Buildings (NZEBs). Within EU-funded project iClimaBuilt, RISE is developing and improving the formulation of cellular lightweight concrete insulation (CLC) as a sustainable and recyclable alternative for organic insulation materials (ex. Expanded polystyrene (EPS)). Compared to EPS, this material is non-combustible and achieves similar performance as existing insulation materials (thermal conductivity of 40 mW/(mK)) while economically more attractive (EPS 60 EUR/m3, CLC 50 EUR/m3). In addition, the material is easily recyclable since it is 100% mineral based. It is also similar or lighter in weight than traditional EPS (around 80 kg/m3). At these ultra-low densities as for concrete, the material integrity was ensured by adding polypropylene micro-fibres. To further improve the thermal conductivity of CLC, granulated silica aerogels were implemented in the mix. The CLC was implemented in a lightweight sandwich-panel in form of a prefabricated block similar to currently used EPS-sheets. The recyclability of the material as an SCM for new cement production is being evaluated by a reactivity study of grinded and reheated (recalcined) material. The panel prototypes will be tested in a laboratory and validated in the living labs – real-life test and experimentation buildings in different climate zones in Europe.

Jan Suchorzewski, Natechanok Chitvoranund, Sumit Srivastava, Miguel Prieto, Katarina Malaga
Clay Brick Powder as Partial Cement Replacement

In this study, waste clay brick powder (CBP) from a Danish recycling plant was studied with the aim of using the material as a partial cement replacement to reduce the need for cement in cementitious products. The focus is on the fineness of the CBP and its influence on the compressive strength, reactivity of the CBP, and phase development of cement pastes containing CBP over time.The CBP was characterized with respect to mineralogy, Loss on Ignition and thermogravimetric analysis (TGA), particle density, Frattini test, and particle size distribution. The powders were produced by ball milling or disc milling the brick waste, and, thus, CBPs based on the same raw material but with different particle size distributions were produced.Mortar specimens were produced with two CBPs, which were based on the same raw material: CBP-C (coarser powder) and CBP-F (finer powder) added in fractions of 0, 10, 20, and 30 wt% to analyse the effect of the powder fineness on the compressive strength at 28 days. The results showed that the reference (0 wt%) and 10 wt% replacement levels obtained the same compressive strength. Regarding the fineness, the addition of 30 wt% CBP-F resulted in a slightly higher compressive strength compared to that with 30 wt% CBP-C.The reactivity and phase development of the CBP was further studied in cement paste samples containing 0 wt% (reference) and 20 wt% CBP. The pastes were studied using X-ray diffraction (XRD) and TGA at different curing times. The TGA measurements revealed a higher amount of bound water for the pastes containing CBP (normalized to the clinker content). From the XRD measurements, the development of mono-carbonate exceeded the formation of hemi-carbonate, which could explain the higher amount of bound water.Overall, it was found that replacement levels of 10–20 wt% of cement with CBP resulted in good compressive strength of the mortar specimens, which means that it seems possible to replace up to 20 wt% of the cement in cementitious products. However, further research is necessary and longer curing times would be interesting to study.

Ida M. G. Bertelsen, Sissel A. Kahr, Wolfgang Kunther, Lisbeth M. Ottosen
Mineral Residues and By-Products Upcycled into Reactive Binder Components for Cementitious Materials

In contrast to granulated blast-furnace slag (GBFS), many other industrial residues and by-products such as steel slags are currently not utilised to produce hydraulic or alkali-activated binders. Simultaneously, the building materials industry is confronted with steadily growing demands for increased CO2 and resource efficiency, as well as dwindling supplies of traditional supplementary cementitious materials. This contribution covers the characterisation of slag-like compounds prior to and after carbothermal treatment, with respect to their utilisation potential as binder components. The treated materials were highly amorphous with a favourable chemical composition - particularly high contents of CaO, SiO2, Al2O3 and MgO, high (CaO+MgO)/SiO2-ratios (>1.0, ideally > 1.2) and low amounts of unwanted impurities like Fe- and Mn-containing compounds. Subsequent characterisation of the reactivity of the processed materials revealed high hydraulic activity (activity index up to >100% after 28 days) and suitability for alkali-activation. In contrast, the untreated materials showed only insufficient hydraulic activity but could successfully be used as binder components in alkali-activated materials. Chemical indices based on the amorphous content and the content of CaO, MgO, Al2O3, SiO2, FeO and MnO were identified as suitable control parameters for estimating the potential hydraulic activity of slag-like materials.

Florian Roman Steindl, Klaus Doschek-Held, Katharina Weisser, Joachim Juhart, Cyrill Grengg, Dominik Wohlmuth, Florian Mittermayr
Study of Hydration Properties for Blast Furnace Slag-Blended Cement: Prediction of Slag Hydration Kinetics

Blast furnace slag (BFS) is an industrial by-product that has been used to replace clinker in Ordinary Portland Cement (OPC) to reduce the CO2 footprint impact in the construction field. Moreover, the use of BFS leads to an enhancement in terms of mechanical and durability properties. A solid comprehension of hydration properties is essential to achieve a better understanding of durability properties. In this context, this study deals with the hydration processes (BFS)-blended cement in terms of kinetics. For that purpose, a simplified analytical model is proposed to get the evolution of the hydration degree in time. The input data required are the formulation parameters, i.e., water-to-cement ratio (W/C) and the fraction of slag used respectively. The model is validated with experimental measurements of the evolution of the hydration kinetics, based on the results of a ThermoGravimetric Analysis (TGA), which are performed on different cement pastes formulated with BFS-blended cement. Finally, the present study is supplemented by a comparison between the results obtained by the TGA method and those provided by open-source software (VCCTL).

Mohamad Ali Ahmad, Harifidy Ranaivomanana, Stéphanie Bonnet, Valérie L’Hostis, Paul Buttin
Binary and Ternary Shale Binders with High Replacement Levels

This paper investigates mortars with fifty percent cement replacement of supplementary cementitious materials in binary and ternary blends, according to DS/EN 197-5: 2021. A new standard that allows for up to 50% of cement replacement levels than previously. Different aspects ranging from rheology, mechanical properties, and mineralogical changes were measured. The selected shale was ground in a laboratory disk mill, blended and tested in binary blends (only shale), and together with limestone filler as ternary blends. As expected, the mechanical properties of these mortars are lower than the mortar made only with Portland cement. The binary binder, with 50% cement replacement by calcined shale alone, developed larger compressive strengths and larger reductions in portlandite than the ternary binder, due to the additional pozzolanic reactions. The replacement of one-third of the shale by limestone filler, with a total cement replacement of 50%, had the lowest compressive strength values but less superplasticizer demand for the target workability. This allows, when judged by the rheology and mechanical properties alone, a mixture of both SCMs might be beneficial, for example where no risk of corrosion would be expected (X0, XC1). Furthermore, one might consider the optimization of the relation between the calcined shale and limestone where CO2 emissions are being reduced.

Wolfgang Kunther, Lasse Nørbye Døssing
Influence of Rice Husk Ash on Rheology of Conventional Concrete

Conventional concrete was prepared for 10%, 15% and 20% volumetric cement replacement by a valorised Rice Husk Ash (RHA) and its rheology was evaluated using a coaxial rheometer. Flow behaviour in terms of dynamic yield stress and plastic viscosity was examined using torque (T) vs rotational speed (N) results obtained from the rheometer. T-N results were analysed using a suitable rheological model. The static yield stress of concrete was also investigated using torque vs time graphs obtained from the stress growth test in the rheometer. Results show that for each RHA replacement, the plastic viscosity in concrete increased compared to the control concrete, whereas dynamic yield stress decreased beyond 10% RHA replacement level. As the RHA percentage increased from 10% to 20%, plastic viscosity increased 1.5 to 3 times compared to the control concrete. The static yield stress of RHA blended concrete also increased significantly after incorporating RHA, which is an indication of increased flocculation in RHA blended concrete. RHA blended concrete was found eco-friendly as the global warming potential and embodied energy was lower than the control concrete.

Arshdeep Singh, Bhupinder Singh
The Influence of Gypsum Content on the Hydration and Properties of Belite-Ye’elimite-Ferrite (BYF) Clinker

Belite-ye’elimite-ferrite (BYF) cements are considered an environmentally friendly alternative to ordinary Portland cement due to their lower carbon dioxide (CO2) emissions and reduced energy requirements. However, their hydration mechanism and its effect on strength development have still to be clarified. Therefore, this study aimed to investigate the influence of gypsum contents on the hydration behavior and strength development of laboratory-prepared BYF cement.The studied cements were made from a clinker, produced at 1250 ℃, containing approximately 50% of belite (C2S), 30% of ye’elimite (C4A3$), and 20% of ferrite (C4AF) as the main phases. Phosphorus pentoxide and lithium oxide were added to the clinker to stabilize the α’H-C2S. The phase assemblage of the cement pastes was characterized by quantitative X-ray diffraction using Rietveld refinement at different ages. TGA and DSC methods were used to confirm the XRD data and to characterize the main amorphous hydrate phases. The hydration kinetics was studied using isothermal calorimetry for seven days. The strength development of BYF mortars with a water-to-cement ratio of 0.50 was studied for up to 56 days.The results showed that the optimal content of gypsum was 18 wt % due to the higher strengths at all ages and higher heat generation during hydration. Increasing the amount of gypsum increased the content of ettringite. In contrast, the content of strätlingite, the main hydration product of belite, decreased, and the content of unreacted belite in the cement increased. This indicates that the amount of gypsum strongly affects the hydration rate of belite.

Adam Sabbah, Semion Zhutovsky
Possibilities for Application of Modified Solidified Water Treatment Sludge as Supplementary Cementitious Material

The increased number of water treatment plants induces intensified production of water treatment sludge (WTS) that needs to be stabilized and reused. One of the possible stabilization processes is solidification, which involves the reaction of wastes with additives based on calcium-oxide and calcium-hydroxide. The final product of these reactions (solidified water treatment sludge - SWTS) is an inert material that can be used as a filler, but not as a supplementary cementitious material (SCM) - due to its insufficient pozzolanic activity. The paper presents the possibilities of application of modified SWTS (MSWTS) as a SCM when mixed with aluminium-oxide and magnesium-silicate. In order to achieve this, mortar mixtures were prepared with partial replacement of cement by using MSWTS in amounts of 10%, 20% and 30%. Flexural and compressive strength tests, together with ultrasonic pulse velocity, as well as with capillary water absorption and freeze-thaw resistance were performed. The obtained results point to the conclusion that the increase in the percentage content of MSWTS consequently led to a decrease in the mechanical properties of the tested samples, which limits the possible cement percentage replacement in plasters. The decrease in flexural strength ranged between 3% and 8% and in compressive strength between 8% and 19%.

Marina Aškrabić, Dimitrije Zakić, Aleksandar Savić, Aleksandar Radević, Ivana Stojanović
Alternative Cementitious Binders Using Mineral Wastes

The present study discusses preliminary findings on the potential of upcycling mine tailings into an alternative source of supplementary cementitious materials. Thermal and mechanical activation mechanisms were used to alter the highly crystalline microstructure of the raw tailings. Scanning and transmission electron microscopy and X-ray diffractometry were used to investigate morphological and microstructural features. The R3 test was used to assess the chemical reactivity of the processed mine tailings and benchmark their behaviour against widely used supplementary cementitious materials such as microsilica and fly ash. The results showed that indeed the followed activation mechanisms have gradually amorphized the raw tailing, yielding it eligible to participate in chemical reactions within a cementitious matrix.

Surya Maruthupandian, Antonios Kanellopoulos
Characterization of Pozzolans to Use as Supplementary Cementitious Material in Concrete Through X-ray Diffraction

The most common approach for qualitative analysis of distinct phases of a material is X-Ray Diffraction analysis (XRD). This paper assesses the suitability of a material to be used as a supplementary cementitious material in the production of concrete. Different test procedures such as pozzolanic reactivity, can be used to determine the suitability of material to use as a pozzolan in concrete production. Microstructural aspect like x-ray diffraction is one such parameter which serves the same purpose qualitatively. This paper investigates the suitability aspects of mining waste like slime, kimberlite and clay dust using x-ray diffractometer through phase identification, crystallinity, and crystal lattice structure. These findings indicate kimberlite and clay dust can be employed as pozzolans which exist in orthorhombic and primitive cells of phases such as chrysolite, quartz, and alumina oxide.

P. J. R. L. P. Susmitha, Pramod Kumar Reddy Yeturi, Sri Kalyana Rama Jyosyula, Visalakshi Talakokula
Development of Low Carbon Textile Reinforced Concrete from Composite Cements

Textile reinforced concretes (TRCs) are innovative materials composed of continuous reinforcement fabrics embedded in a cement-based matrix. The excellent mechanical and durability properties of these composites have attracted extensive attention for the repair of existing structural components or for the development of new ones. To address the need for increasing the sustainability of construction materials, this study presents an experimental effort to replace the matrix of TRCs with low carbon concretes. For this purpose, a range of quaternary blended cement mixes made of Ordinary Portland Cement, Fly Ash, Limestone and Silica Fume (with 70% cement replacement levels) were developed. The mixes achieved the target compressive strength and the workability were used for the development of Glass-based TRCs. Flexural tests performed on the developed TRC composites show an improvement in the ultimate flexural strength and strain and a reduction of the environmental impact and cost compared to the common TRC composites available in the literature.

Mohammad Alma’aitah, Bahman Ghiassi
Evaluation of the Pozzolanic Activity of Copper Slag through Paste and Mortar Studies

Ferrous and non-ferrous slags generated in huge quantities in the past few decades as a result of increased demand for metals. Slags from non-ferrous metallurgy can be of interest to find their potential application in construction to solve the problems related to dumping, disposal, environmental issues, etc. The current work focuses on understanding the reactivity of non-ferrous copper slag (CS) when used as a supplementary cementitious material (SCM) for partial replacement of ordinary Portland cement (OPC) 53 grade. Raw granular CS was processed in a laboratory ball mill to obtain finer powdered material. Well-established pozzolanic material, Fly ash (FA) was used in the study for comparing the reactivity of CS. Reactivity studies were carried out on CS-calcium hydroxide (CH) (in suspension) and OPC-CS pastes through the thermogravimetric analysis (TGA) technique. A mortar sample study was performed for the determination of compressive strength with 25% weight replacement of CS and FA in OPC. Mortar samples were steam cured for 12 h at 65 ℃ to check the effect on early age strength development. Compressive strength was determined at the age of 1, 7, 28, and 90 days. CS consumes CH as observed from the results of the paste study. Results indicate that CS does show pozzolanic properties. The reactivity of FA was higher compared to CS as evident from paste and mortar studies. CS-incorporated mortar samples achieved about 80% of the compressive strength compared to the control sample (100% OPC) strength at 90 days of testing.

Dhiraj Surendra Mahajan, Muhammad Salman
Exploration of Waste Glass Powder as Partial Replacement of Cement in Concrete

This paper shows that combining the knowledge of relevant chemical compounds and chemical reactions associated with cement hydration together with the chemical compounds in glass can be used to establish the right use of waste glass powder as a partial cement replacement in concrete. The results show that Calcium Hydroxide (Ca(OH)2), which is a by-product of the hydration of Portland cement, reacts with Silicon Oxides (SiO2) in glass powder ensuring the formation of strength imparting compounds Calcium–Silicate-Hydrate (C-S-H), in addition to the C-S-H formed due to the hydration of regular calcium silicate compounds (C2S - Di-Calcium Silicate and C3S- Tri-Calcium Silicate) in cement. A method to establish the optimal cement replacement percentage based on the amount of total C-S-H formed in the mix is presented in the paper. For example, with C3S and C2S compositions of 54% and 20.7%, respectively, of the cement used in the present study and 70% silica in the glass, the optimal cement replacement percentage by glass powder is determined to be 19%.

Gaurav Chand, Mithila Achintha, Yong Wang
Interfacial Transition Zone Formed on Wet-On-Wet Cast Between Ultra–High–Performance Fiber Reinforcement Concrete – Blast Furnace Slag Concrete

The concrete, which is the most common material used after water, is associated with emissions of large amounts of CO2 related to the Portland cement which is responsible for a total 5–8% of the global CO2. The manufacture of hybrid concrete elements allows the use of the cement to be optimized and minimized by replacing it with secondary cementitious materials. Replacing the cement with secondary cementitious materials can help in reduction of CO2 footprint but unfortunately it may result in slower strength development and low durability of the produced concrete. This study investigates the potential of casting simultaneously vertically layered prismatic elements composed of an external durability layer and an internal ecological concrete layer to minimize the cement usage. Interfacial transition zone (ITZ) formed between the two casted concrete is the key factor that determines the bond strength and durability of the structure. In this study bond behavior and micro – properties of the wet-on-wet casting interface of ultra–high–performance fiber reinforcement concrete (UHPFRC) – blast furnace slag concrete (BFSC) is investigated. The investigation includes flexural bond strength test and backscattered electron microscope (BSE) for analyses of micro – properties. The flexural strength test showed a good bond formed between UHPFRC and BFSC casted on wet-on-wet. The microstructural investigation confirmed a dense zone in the interface where the porosity and phase composition change gradually from the inner layer to the outer layer of the hybrid concrete.

Klaudja Telhaj, Andrzej Cwirzen
Development of Low-Carbon Lightweight Concrete Using Pumice as Aggregate and Cement Replacement

An experimental investigation was conducted to develop a low-carbon lightweight aggregate concrete (LWAC) using naturally occurring aggregates and evaluate its mechanical performance. Lightweight aggregates used in structural concrete are commonly manufactured from recycled pulverised fuel ash or expanded clay, which require high temperatures during production. Additionally, the availability of traditional supplementary cementitious materials used in concrete, such as Ground Granulated Blast Furnace Slag (GGBS), is diminishing. Therefore, more environmentally friendly alternatives are required. Pumice, a naturally occurring lightweight stone formed due to the rapid cooling of magma from volcanic eruptions, poses a promising candidate for using as lightweight aggregate, whilst it might also exhibit pozzolanic properties that make it suitable as a cement replacement material. Therefore, the present study is focused on examining the development of low-carbon LWAC mixes with pumice as coarse aggregate and ground pumice as cement replacement. In addition, a novel recycled waste known as Lytash was trialed as a filler. This is a by-product of the manufacture of fly-ash based lightweight aggregates (commonly known as Lytag, which is in itself is a recycled by-product from coal fired power plants). The fresh and hardened densities of concrete were evaluated as well as the compressive strength (targeting a strength class LC30/33). It was found that lightweight aggregate concrete with a density of less than 1800 kg/m3 was possible to achieve. Furthermore, the pozzolanic reactivity and X-Ray Diffraction (XRD) testing; as well as the 28 days compressive strength of samples tested revealed the potential of pumice powder to be used as a cement substitute. Embodied carbon calculations were also carried out accentuating the savings in carbon footprint that can be achieved with pumice aggregate and powder.

Ali Abbas, Mathura Mahadevan, Saru Prajapati, Bamdad Ayati, Fragkoulis Kanavaris
Hourly-Repeated Three-Minutes Creep Testing of a Limestone Calcined Clay Cement Paste (LC3)

Early-age characterization of cement pastes, mortars, and concretes is important for the design of engineering structures which are made of cementitious materials and loaded at early ages. This paper provides an overview of early-age mechanical testing methods regarding the strength, stiffness, and creep properties of cement-based materials. Uniaxial compressive strength tests, ultrasound pulse transmission tests, and hourly-repeated three-minutes creep tests are then performed to characterize two types of cement pastes. They are made from an ordinary Portland cement (OPC) and an LC3 system containing 70% OPC, 15% calcined clay, and 15% limestone. The hourly-repeated three-minutes creep tests are started at material ages of one day, and they are kept running until the materials are seven days old. The comparison of results obtained from both types of tested materials will improve the mechanical understanding of LC3 systems which are a promising alternative to traditional Portland cement, because they significantly reduce the CO2 emissions associated with the production of concrete.

Sophie J. Schmid, Luis Zelaya-Lainez, Olaf Lahayne, Martin Peyerl, Bernhard L. A. Pichler
Reactivity of Mixed Layer Clays – The Effect of Polycarboxylate Based Superplasticizers on Effective Particle Size Distributions

The declining availability of promising supplementary cementitious materials (SCMs) in the recent past, such as fly ash and ggbfs, has opened new recesses in the domain of alternative binders. It is therefore imperative and urgent to develop more lasting and consistent alternatives, for addressing the need to diminish the carbon footprint of cement production. The potentialities of utilizing mixed layer excavated clays that are obtained as by-products of repair and construction activities, as possible SCMs have been well established in past literature. However, understanding the relationship between particle deagglomeration and pozzolanic properties via non-energy-intensive methods, is still an open niche yet to be fully explored. This study is an attempt at understanding the use of dispersive mechanisms such as super-plasticizers and storage in suspension to possibly impact surface charges of clay agglomerates and eventually, their reactivity. It is found that dispersive agents added to ground clay particles can enhance pozzolanicity of mixed layer clay particles and thereby reduce dependence on energy intensive methods such as grinding for activation.

Amrita Hazarika, Arezou Babaahmadi
Using Non-standard Concretes in a Major Infrastructure Project: A Multidisciplinary Approach for Implementation

The interdisciplinary collaborative process employed to unlock the use of alternative Supplementary Cementitious Materials (SCMs) that are not yet fully standardised or widely tested on a tunnelling project for high-speed railway in the UK is presented. This case study is focused on implementing more resource efficient and less carbon intensive concrete mixes compared to conventional ones, specifically through using Alkali Activated Materials (AAMs) and calcined London Clay as SCMs initially for low-risk applications, such as unreinforced tunnel walkways, to help prove these concepts.The ability to confidently use such novel products with lower carbon footprint and better environmental credentials is key for timely decarbonisation of the construction industry. However, the current lack of or partial standardisation for such concretes is, amongst other factors, inhibiting their wider uptake. Additional challenges arise on major infrastructure projects with long design lives (over 100 years) with regards to ensuring the required durability and long-term technical robustness of the works.Tunnel walkways are initially selected for applying the AAM and calcined clay concrete in this case. The paper describes the steps undertaken by the SCS JV to enable the use of non-standard concretes on the High Speed 2 (HS2) railway project. The importance of multidisciplinary collaboration needed for successful implementation of lower carbon concretes is highlighted: structural design, materials science & concrete technology, tunnelling construction, environmental sustainability, commercial & procurement; and project stakeholders: client, designer, contractor & supply chain; were engaged to build the case, balancing environmental benefits with potential risk, programme and costs.

Athina Papakosta, Apostolos Tsoumelekas, Wolf Wichman, Fragkoulis Kanavaris

Alkali-Activated and other Non-Portland Cement Based Materials

Effect of Activator Solutions on the Thixotropic Behavior of Alkali-Activated Slag Concrete

Alkali-activated material (AAM) is developed as a green alternative binder to replace Portland cement (PC) in the construction field. However, the large-scale application with AAM concrete is limited so far, with the insufficient knowledge of rheological behavior being a major obstruct.Thixotropy of concrete is of great interest, which can be helpful to predict various early-age performances. The current study dedicates to evaluating the thixotropy of alkali-activated slag (AAS) concrete mixtures with different silicate and water content in activator solutions. In specific, the silicate modulus (Ms) and water to binder (w/b) ratio have been varied. The thixotropic index calculated by the initial and equilibrium shear stress from the stress growth test, as well as the breakdown area obtained by applying different shear speeds were used to evaluate the thixotropy of AAM concrete. Results indicate a good correlation between different approaches. It was found that an increase in Ms led to more pronounced thixotropic behaviors in AAS concrete due to the rapid nucleation and accumulation of early hydration products, resulting in significant increases in peak torque values and slight reductions of torque at equilibrium. Besides, the concrete thixotropy gradually declined by applying a higher w/b ratio.

Yubo Sun, Saeid Ghorbani, Guang Ye, Geert De Schutter
Investigation of the Properties of Geopolymer Mortars Produced with the Construction and Demolition Waste

Considering the production of a tremendous amount of construction and demolition waste (CDW) worldwide, it is necessary to develop new-fashioned and sustainable methodologies for the value-added upcycling of these wastes. In that context, this study focused on the utilization of CDWs in geopolymer production. Besides, the effects of different types of industrial wastes on the mechanical and fresh properties of CDW-based geopolymers were investigated. The designed blends containing different types of CDWs (hollow brick, red clay brick, roof tile, glass, and concrete wastes) and industrial wastes (fly-ash, slag, and silica fume) were activated by different combinations of NaOH and Ca(OH)2. The concrete waste was used as fine aggregate. Flow table, buildability, and vane shear tests were performed for fresh property assessments. Besides that, the mechanical performance of geopolymer mixtures was evaluated by conducting compressive strength tests. Results showed that CDW-based precursors have the potential to be used in geopolymer production for valuable recycling. The incorporation of industrial wastes into the CDW-based geopolymer mixtures caused an enhancement in the workability. In addition, the mechanical properties of the CDW-based geopolymer mortars were improved with the inclusion of industrial wastes. It is believed that the findings of this study will contribute to the current literature by proposing a different way of producing novel CDW-based geopolymers in favor of sustainability.

Hüseyin Ilcan, Oğuzhan Şahin, Ehsan Aminipour, Mustafa Şahmaran
Effect of Internal and External Factors on the Volume Changes of Slag Binder Activated by Sodium Hydroxide at Early-Age

As concrete is the second most used material after water, representing 5% to 7% of global anthropogenic CO2 emissions, it is crucial to decrease its CO2 production. One way to reach this goal is to use alkali-activated materials. It is known that they have adequate mechanical properties for the construction sector. However, alkali-activated materials suffer from significant early-age volume changes such as autogenous and thermal strains. Factors such as the amount of solution, activator type, molarity, curing conditions and internal relative humidity have an important influence on how the early-age volume develops. The objective of this research is to study the impact of internal (solution-to-binder ratio) and external (curing temperature) parameters on the autogenous strain of slag activated by sodium hydroxide. A revisited version of the AutoShrink device, developed at ULB, has been used to determine the autogenous strain as well as the coefficient of thermal expansion (CTE) through temperature cycles applied to the samples since casting. In a general way, increasing the solution-to-binder ratio has a magnifying effect on the cumulative heat while the autogenous shrinkage decreases. Moreover, increasing the solution-to-binder ratio and the curing temperature leads to a higher autogenous swelling of the paste after setting. Decreasing the curing temperature results in a lower heat flow while the autogenous strain increases in magnitude. The increase in the CTE is proportional to the increase in the solution-to-binder ratio. Additionally, lowering the temperature induces a decrease in the CTE.

Maïté Lacante, Brice Delsaute, Stéphanie Staquet
Taguchi Method for Optimizing Alkali-Activated Mortar Mixtures Using Waste Perlite Powder and Granulated Blast Furnace Slag

This paper aims to find the optimum proportions of alkali-activated mortar mixtures made with waste perlite powder (PP) and granulated blast furnace slag (BFS) for superior fresh and mechanical performance. The PP-BFS blended mortar mixtures were developed using the Taguchi method. Four factors, including the binder content (500, 550, and 600 kg/m3), PP replacement percentage by BFS (25, 50, and 75%), alkali-activator solution-to-binder (S/B) ratio (0.60, 0.65, and 0.70), and sodium silicate-to-sodium hydroxide (SS/SH) ratio (1.0, 1.5, and 2.0), were considered in the design phase. Accordingly, an L9-sized orthogonal array was developed, leading to a total of nine alkali-activated mortar mixtures. The target design criteria were the flow and 7-day compressive strength. The analysis of variance (ANOVA) revealed that the S/B and SS/SH ratios contributed the most to the workability of mixes. Conversely, the PP replacement by BFS was the controlling factor among others on the 7-day compressive strength. Using the Taguchi method, the optimum mix proportions for superior flow ability were binder content of 500 kg/m3, WPP replacement percentage by BFS of 25%, S/B ratio of 0.70, and SS/SH ratio of 1.5. Meanwhile, the highest strength response was attained while using a binder content of 600 kg/m3, WPP replacement percentage by BFS of 25%, S/B ratio of 0.6, and SS/SH ratio of 2.0.

Joud Hwalla, Abdulkader El-Mir, Hilal El-Hassan, Amr El-Dieb
Evaluation of the Cracking Risk in Alkali Activated Materials by Means of Restrained Shrinkage

Early age micro-cracks development is the source of many durability issues of concrete structures. Specifically, crack formation caused by restrained deformation takes place at a time when the properties of the material are still evolving and its deformation rate is high. The present study used the ring test to investigate the early age cracking sensitivity in restrained conditions of NaOH activated slag. In addition, several parameters were considered, such as the molarity of the activating solution, and the solution-to-binder ratio. An increase in the solution molarity leads to higher compressive strength, autogenous shrinkage, and internal stress, while increasing the solution quantity produces the opposite effect: compressive strength, autogenous shrinkage, and internal stress decrease. Moreover, the internal stress has been compared with the tensile strength of the material showing a good agreement between experimental and modelled results and the low influence of viscous properties of the material at early age. From a general perspective, it has been observed that autogenous shrinkage is the main phenomenon influencing the early age cracking behaviour of alkali-activated slag, whereas creep does not act significantly as a relaxation factor and reduces the internal stress and strain, and the cracking risk.

Marco Sirotti, Sarah Blomart, Brice Delsaute, Stéphanie Staquet
Strength and Durability Assessment of Geopolymer Mortars Based on Non-calcined Dredged Sediments

On the eve of changing laws concerning dredging practices, the recovery of sediments is necessary to create a viable economy for their management. With the evolution of the global environmental context which invites companies to reduce their impact by reusing local materials, dredged sediments represent a potential source of material. Thus, the objective of this study is to develop an ecological concrete via the use of geopolymers that can be poured on site for public works close to the Ports. Recent studies showed that the development of a geopolymer phase when mixing sediments with an alkali reagent is viable due to their mineralogical and chemical composition. However, due to the use of sediments in their natural state, high setting times and shrinkage were observed which could prevent their valorisation. Therefore, this study aims to improve the developed mortars through the co-valorisation of marine sediments with Supplementary Cementitious Materials (SCMs) such as metakaolin and ground granulated blast furnace slag. The sediment-based geopolymer mortars has been analysed through macroscopic and mineralogical tests. The durability has been also studied in order to validate the viable use of sediment based geopolymer mortars. The results showed that the use of metakaolin could be beneficial to improve the compressive strength and durability of the mortars compared to ground granulated blast furnace slag where calcium could be detrimental to the reactions kinetics.

Lisa Monteiro, Jacqueline Saliba, Humberto Yanez-Godoy, Nadia Saiyouri
Monitoring and Modeling of Visco-Elastic Strains of Alkali-Activated Slag Mortar Since the Earliest Age

This research examines the evolution of visco-elastic strains of sodium hydroxide-activated blast furnace slag mortar (with two different molarities of the activator solution) since the earliest age. Two distinct load durations, a short loading lasting five minutes is repeated hourly and a long loading lasting several weeks is applied on the aging material to monitor the development of elastic and creep strains. The tangent elastic modulus as well as the Poisson’s ratio are computed by linear regression (from the load vs displacement recordings) between 20% and 80% of the applied loading. A power-law creep function is used to model the short-term creep behaviour, while for long-term creep, a logarithmic creep function is used. Furthermore, for a long duration of loading, a logarithmic trend is observed in the development of the specific creep. An adapted Model Code 2010 is used to fit the experimental data that shows good agreement to model the specific creep of slag-based mortar samples.

Ali Naqi, Brice Delsaute, Markus Königsberger, Stéphanie Staquet
Delayed Deformations of Na- and K- Sulphates Activated Blast-Furnace Slag Mortars

Alkali sulphates are chemical products that can be used to activate and improve the performance of mineral additions, like Blast-Furnace Slag (BFS) and Fly Ash (FA). This study investigates the effect of two alkali sulphates (sodium sulphate and potassium sulphate) on delayed deformations of mortars containing a high content of BFS. Autogenous shrinkage is monitored after 2 days and basic creep tests are conducted on 28-day-old specimens loaded at 30% of their compressive strength. Their microstructure is characterized by using several experimentations, such as internal relative humidity measurements, thermogravimetry analysis and a water porosity test. A numerical model in terms of C-(A)-S-H content evolution is applied to quantify the degree of hydration advancement. The results show that the use of sodium sulphate leads to a higher autogenous shrinkage, but to a lower specific creep. This is linked to the fact that the mortars activated with sodium sulphate show a faster hydration rate and a lower porosity, which results in higher capillary pressures. However, this also limits the movement of water required for creep development.

Lei Li, Kinda Hannawi, Aveline Darquennes
Effect of Aggregate Skeleton and Admixtures on Fresh and Hardened Properties of High-Strength Geopolymer Mortars

On account of growing environmental and economic concerns, decarbonization of the concrete industry has become a priority with the development of environmentally friendly building materials to attract both research community and industry. A class of advanced environmentally friendly building materials is geopolymer mortars. Their production incorporates mostly industrial by-products in lieu of cement which has a double benefit in terms of sustainability: recycling industrial wastes instead of harmful disposal and reducing carbon footprint by eliminating cement. Although geopolymer mortars have similar or enhanced performance compared to conventional mortars, their development and optimization techniques are vastly different. This study explores two optimization techniques widely used in the development of high-strength and high-performance mortars, namely the use of chemical admixtures and particle packing theory. More specifically ten different admixtures and six different sand contents based on packing density were investigated along with their effect on fresh and hardened state properties such as workability, setting time, and compressive strength, respectively. Higher sand contents improved the compressive strength, while slightly compromising the workability. Finally, it is observed that chemical admixtures developed for OPC concretes are not ideal for geopolymer concretes and interventions such as reducing the temperature of the mixing components could be an effective method to manipulate fresh state properties without compromising the mechanical strength.

Zoi G. Ralli, Stavroula J. Pantazopoulou
Effect of Organic Retarders on Fluid-State and Strength Development of Rock-Based Geopolymer

Granite waste is rich in aluminum and silicate has the potential of turning to geopolymer material after mixing with an alkali solution. One of the challenges in developing a geopolymer is to select a suitable retarder to adjust the target pumpability while maintaining workability and followed by a proper strength development rate. In this study, the effect of five selected organic retarders on workability, viscosity, and compressive strength has been examined. Sucrose, a calcium chelator, gluconic acid, sodium lignosulphonate, and ionic liquid were selected as candidate retarders. The experiments were carried out at room temperature according to American Petroleum Institute (API) standards for testing well cement. The tested retarders indicated a secondary effect on fluid-state properties. The reasons for the secondary effect are due to either the change in the pH of slurries or the interaction between ions released from the retarder and the geopolymer precursor. Gluconic acid and sucrose provided a longer setting time, while they significantly lowered the strength development in the short-term. Lignosulfonate had less impact on workability. However, it reduced viscosity and yield stress. All retarders influenced the strength development rate, but the sodium lignosulfonate, chelator, and ionic liquid had a negligible impact on final strength after 14 days of curing.

Mohammadreza Kamali, Mahmoud Khalifeh, Samindi Samarakoon, Saeed Salehi, Yuxing Wu
Effect of SiO2/Na2O Ratio on the Fresh and Mechanical Properties of Binary Blend Alkali Activated Mortar Incorporating Copper and Blast Furnace Slags

In recent years, alkali activated concrete technology has gained growing attention due to its potential advantages compared to Portland cement (PC) based concrete, in terms of environmental and economical contribution. Ground granulated blast furnace slag (GGBFS), which is used as a common precursor to produce alkali activated materials (AAMs) is becoming less available compared to the past due to its high consumption. Therefore, the use of alternative precursors such as copper slag (CS) to produce AAMs can be considered as a potential solution. In the present study, the effect of the SiO2/Na2O ratio on the fresh and mechanical properties of slag based alkali activated mortar mixtures incorporating of 50% CS as partial replacement of GGBFS has been studied. A total of three AAM mortar mixtures were produced using three different SiO2/Na2O ratios of 1.0, 1.3 and 1.6, respectively. The flow spread and fresh density of the AAM mixtures were comparable to that of PC based reference mixtures. The flow spread behaviour of the AAMs mixtures was improved slightly (14%) by increasing the molar ratio up to 1.3. Compressive and flexural tensile strength values of within the range 81–86 MPa and 7.8–8.5 MPa, respectively are obtained after 28 days. The strength properties of the mixtures increased and then decreased by increasing the SiO2/Na2O ratio from 1.0 to 1.3 and 1.3 to 1.6, respectively. For the studied binary mixtures and ranges of SiO2/Na2O ratios, the SiO2/Na2O ratio of 1.3 can be considered as an optimum value in terms of strengths properties.

Saeid Ghorbani, Kobe Petters, Stijn Matthys
Influence of Slag Chemistry on the Carbonation of Sodium Sulfate-Activated Slag Cements

In this study, the carbonation resistance of sodium sulfate-activated slag cements was determined. Three slags with different compositions were evaluated. Solid specimens were exposed to natural carbonation for a period of up to 60 days under controlled environmental conditions (23 oC and 65% relative humidity). Specimens were also subjected to accelerated carbonation at 1% CO2 concentration for a period of 28 days, under similar environmental conditions to those adopted for natural carbonation. The phase assemblage evolution post-carbonation was studied using X-ray diffraction and scanning electron microscopy. Results confirmed that the slag chemistry and CO2 concentration influence the type of CaCO3 polymorphs forming in these systems upon carbonation. These materials also present different carbonation rates as a function of the exposure conditions, and binders produced with the slag with the higher Mg/Al ratio seem to have a higher carbonation resistance compared with other cements evaluated. Although very rapid carbonation was observed under accelerated conditions, naturally carbonated conditions did not present a visible carbonation front after 60 days, when measured using the phenolphthalein indicator method. Results suggest that the accelerated carbonation conditions tested in this study are too aggressive to replicate in a meaningful way what is observed in natural carbonated specimens for these binder systems.

Zengliang Yue, Yuvaraj Dhandapani, Samuel Adu-Amankwah, Susan A. Bernal
Long-Term Mechanical and Durability Behaviour of Two Alkali-Activated Types of Concrete

A promising solution for reducing the carbon footprint of concrete is the use of alkali-activated concretes (AAC). Before this material can be widely applied, its long-term behaviour needs to be understood, especially since some studies reported a decrease of mechanical properties over time. Similarly, Prinsse et al. reported decreasing mechanical properties, especially elastic modulus and flexural and splitting tensile strength for the studied slag-based AAC (S100) and the blended slag- and fly-ash-based AAC (S50) up to the tested age of 2 years. They hypothesized that these decreases could be only temporarily. To test that hypothesis, this study continued to monitor the mechanical properties of both AACs up to the age of 5 years. As a reference, two OPC-based concretes (OPCC), with different strength classes, are monitored up to the age of 3.5 years. In addition, the internal structures of the concretes are assessed for carbonation and internal micro cracking. S100 shows stabilization of the elastic modulus and the compressive strength, whereas the tensile splitting strength continued to decrease up to 5 years. This is attributed to a combination of carbonation and drying, since the microscopic analysis showed increased porosity around the ITZ and in the carbonated region. In addition, S50 shows an ongoing decrease of all tested mechanical properties, which is attributed to carbonation. No decreases in mechanical properties are found for OPCC.

H. J. Bezemer, N. Awasthy, M. Lukovic
Characterization and Prediction of Clinker Phase Assemblage in Low-CO2 Iron-Rich Calcium Sulfo-Aluminate Cements Incorporating High Volumes of Bauxite Residue

Bauxite residue (BR) is the primary waste product of the alumina industry, with an annual production rate of 170 million tonnes, of which only 4 million tonnes are used productively. As a result, studies are being conducted to determine how high quantities of BR may be included in the manufacture of cementitious products. This research study proposed low-CO2 iron-rich calcium sulfoaluminate cement (CSA-F) by integrating more than 35 wt% BR as a raw material. Using thermochemical modeling, two set of cement clinkers were formulated from the raw materials consisting of limestone, gypsum, kaolin, and BR containing calcium oxide. The main reactive clinker phases targeted were calcium alumino-ferrites (C4AF) and belites (C2S) in the limestone-bauxite residue-kaolin system. However, some minor non-reactive phases such as gehlenite and perovskite were also formed when increasing the BR content in the mixture. Experimentally, a low-BR clinker (38 wt% BR) and a high-BR clinker (50 wt %BR) were produced at a temperature of 1250–1260 ℃, followed by fast cooling to stabilize the reactive phases such as the β-belite phase formed at lower temperatures and increase the hydraulic activity. Results obtained from the experimental characterization studies revealed that in the case of high-BR clinker, non-reactive phases such as gehlenite and perovskite were present, which may reduce the overall hydraulic activity of the clinker. Moreover, the solid solution of ferrite-phase formed in the high-BR clinker had a very low alumina-iron oxide ratio (A/F) which may correspond to low reactivity.

Rahul Roy, Tobias Hertel, Yiannis Pontikes
Early-Age Hydration of an EAF Slag Based Alite–Ferrite Cement Clinker in the Presence of Na2CO3

Reducing the CO2 burden of cement manufacturing can be achieved by increasing the ferrite content in cement as ferrite requires less calcium than other major clinker phases and thus reducing CO2 emission from limestone (mainly CaCO3) calcination. The steel industry produces vast and increasing amounts of EAF (electric arc furnace) slag that consists of calcium, silicon, and iron oxides from scrap steel recycling. Clinkers manufactured using EAF slag as the major component will have a higher ferrite content than traditional clinkers, as EAF slags are rich in iron. The ferrite phase is generally less reactive in polyphase than other major clinker phases; thus, accelerating ferrite hydration by adding carbonates is assessed in this study. Alite-ferrite clinker was produced from EAF slag and pure natural materials at 1450 ºC and the hydration was studied in the presence of dissolved Na2CO3, a low-cost bulk/industrial chemical that provides labile carbonate during the hydration process. The hydration kinetics at different Na2CO3 dosages and water-to-binder ratios were measured using isothermal calorimetry, and the hydrated phases were determined with TGA and XRD. The Na2CO3 dosage increased the ferrite hydration as the monocarboaluminate peak in the XRD data increased with Na2CO3 dosage. We found that there is an optimum soda ash dosage (2.5% by mass of clinker for w/b = 0.35, and 5% by mass of clinker for w/b = 0.45) to accelerate the major alite hydration peak, as confirmed from the calorimetry data and the portlandite content indirectly observed from the XRD and TGA data.

Aniruddha Baral, Visa Isteri, Elijah Adesanya, Juho Yliniemi, Timo Fabritius, Theodore Hanein

Carbon-Based Nanomaterials for Multifunctional Cementitious Matrices (TC 302-CNC)

Development of Self-sensing Cementitious Composites with Improved Water and Chloride Resistance

The piezoresistivity of cement-based sensors subjected to moisture ambient is changeable due to the porous structures and pore solutions inside of cementitious composites. This study explored the electrical resistivity and self-sensing performance of carbon black (CB) filled cement-based sensors mixed with silicone hydrophobic powder (SHP) and crystalline waterproofing admixture (CWA), especially before and after different durations of immersion in freshwater and 3% sodium chloride solution. The results show that the composites with SHP exhibited the best water impermeability, while the counterpart containing CWA presented the optimal chloride resistance. The piezoresistivity increased in sodium chloride solution because of the increased free ions. The outcomes are expected to illuminate the piezoresistive behavior of hydrophobic cement-based sensors subjected to moisture and chloride environments, thereby promoting structural health monitoring applications in the future.

Wenkui Dong, Wengui Li, Marco Liebscher, Viktor Mechtcherine
Resistivity and Capacitance-Based Strain Sensing of CNT and GNP Reinforced Concrete

The accurate stress and strain sensing in concrete is critical for reliable monitoring of its mechanical condition and cracking/failure detection. This work presents results of an experimental study of resistivity and capacitance-based sensing of conducting nanoengineered concrete at all stages of deformation up to failure. While the change in resistivity is widely regarded as the preferred indicator for evaluating the sensing ability of a nanocomposite material, we have shown that piezoresistivity depends on dispersion/exfoliation. Results of the fractional change in resistivity of concrete reinforced with well dispersed/exfoliated carbon and graphene-based nanomaterials, such as carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) showed a piezoresistive signal of 160% at all stress strain levels up to failure. Nanocomposites with as received CNTs and GNPs did not exhibit any change in resistivity during the loading-unloading cycles. The fractional change in capacitance however was adequate for recognizing the change in the applied stress; thus, successfully enabling continuous strain sensing.

Panagiotis Danoglidis, Maria Konsta-Gdoutos
Influence of Carbon Nanotubes Dispersion Degree on the Piezo-Resistive Behavior of Self-sensing Cementitious Composites

Literature reports indicate that Carbon Nanotubes (CNT) are one of the best conductive fillers for self-sensing cementitious composites (SSCC) due to their excellent electrical conductivity. However, due to their Van der Waals interactions and hydrophobic nature, it is a challenge to properly disperse them throughout the cement matrix. Among the known dispersion methods, the use of ultrasonic energy in aqueous media, combined with superplasticizers, has been found to yield good performance. Nevertheless, high amounts of ultrasonic energy can damage the structural integrity of CNT and modify their electrical properties. This work explores how the CNT dispersion degree, obtained from the use of different amounts of ultrasonic energy in aqueous media, affects the self-sensing response of SSCC. CNT aqueous solutions were sonicated in presence of a naphthalene-based superplasticizer and evaluated by means of UV-Vis spectroscopy to characterize their dispersion degree. Cement pastes with different CNT contents were manufactured for each sonication energy and submitted to resistivity and piezo-resistivity testing. Satisfactory self-sensing results were obtained using both high and low sonication energies, associated with good and poor dispersion degrees of the CNT respectively. It was concluded that poorly dispersed CNT can be used to manufacture SSCC by adjusting the CNT concentration.

Claudio José de Aguiar Junior, Pedro de Almeida Carísio, Carlos Fernando Teodósio Soares, Romildo Dias Toledo Filho, Oscar Mendoza Reales
Hierarchical CNT-Coated Basalt Fiber Yarns as Smart and Ultrasensitive Reinforcements of Cementitious Matrices for Crack Detection and Structural Health Monitoring

Basalt fiber (BF) yarns were homogeneously coated with single-walled carbon nanotubes (SWCNT) following a versatile and scalable roll coating wet deposition process. The SWCNT layers turned the intrinsically electrical insulating BFs into highly conductive reinforcements, which were deployed as smart and ultrasensitive sensors for the crack detection of cementitious matrices. A subsequent thermal drying process achieved a uniform and dense SWCNT coating confirmed by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The BF-SWCNT yarns introduced in a cementitious matrix exhibited a significant variation of their fractional resistance change (∆R/R0) upon being exposed to in-situ three-point bending experiments. This response renders the BF-SWCNT as novel strain sensors for cement-based elements possessing high sensitivity factor for crack detection. A subsequent analysis of the fractured surfaces via SEM imaging revealed a good interaction between the reinforcements and the cementitious matrices with adhesive failure mechanisms occurring during the fracture process. The developed BF-SWCNT sensors as model composites of single yarns in a cementitious matrix promisingly envisage the use of CNT-coated BFs for sensing applications in cementitious large-scale composite structural parts or strengthening layers for existing structures.

Marco Liebscher, Lazaros Tzounis, Cesare Signorini, Viktor Mechtcherine
Effect of Carbon Nanomaterials on the Microstructural and Mechanical Properties of Geopolymer Binders

The mechanical and microstructural properties of carbon nanomaterial reinforced geopolymers are investigated regarding carbon nanomaterial type, carbon nanomaterial content, and curing conditions. For this purpose, three types of carbon nanomaterials (CN) were investigated: pristine carbon nanotubes (P-CNT), functionalized carbon nanotubes (F-CNT) and, pristine carbon nanohorns (CNH). The CN were ultrasonically stirred with potassium silicate and a polycarboxylate-based superplasticizer. The homogeneous mixture was stirred with metakaolin, and cured at 20 ℃ and 60 ℃, respectively, for seven days. The different CN proportions were 0.2%, 0.5%, and 1.0% in weight to the amount of metakaolin. Subsequently, flexural strength and toughness were evaluated. The pore structure and pore size distribution were measured by mercury porosimetry. Oven curing at 60 ℃ increased the flexural strength and toughness of all samples. The addition of all types of CN increased the mechanical properties compared to plain geopolymer. Samples with 0.2% F-CNT, cured at 60 ℃, had the highest flexural strength increase of ~ 140%. The increase in curing temperature had the highest effect on F-CNT doped samples. At 0.2%, cured at 60 ℃, pristine CNT and CNH had approximately the same strength increase (~100%). However, at 0.5%, contrary to P-CNT, the pristine CNH samples had a further strength increase (~112%).

Liliya Dubyey, Leon Winn, Neven Ukrainczyk, Eduardus Koenders

Accelerated Mineral Carbonation for the Production of Construction Materials (TC MCP)

Effect of Carbonates on the Formation of Magnesium Silicate Hydrates (M-S-H) and Magnesium Alumino Silicate Hydrates (M-A-S-H)

The effect of carbonates on the formation of magnesium silicate hydrate phases (M-S-H) and magnesium alumina-silicate hydrate phases (M-A-S-H) was investigated in paste experiments at a molar ratio Mg/Si = 1.5, an Al/Si ratio of either 0 or 1 and with and without addition of 1.7 wt. % Na2CO3. M-S-H pastes were synthesised from silica fume and MgO, while M-A-S-H pastes were synthesised from metakaolin and MgO. Thermogravimetric analyses, X-ray diffraction, and 29Si MAS NMR data showed that M-S-H and M-A-S-H phases formed much faster in the presence of sodium carbonate, which destabilised brucite. Furthermore, hydrotalcite formed in the presence of alumina. No evidence of the formation of Mg-carbonate phases in crystalline or amorphous form was observed. The MgO-metakaolin binder reached the highest compressive strength while the MgO-silica fume binder presented a slightly more than the half of the strength. By the addition of sodium carbonate compressive strengths could be improved for both systems.

Ellina Bernard, Barbara Lothenbach, Alexander German, Frank Winnefeld
Carbonation of Concrete Slurry Waste and Its Use as Supplementary Cementitious Material

Concrete slurry waste is generated at concrete plants and generally re-used in new batches of concretes. Due to the presence of hydrated cement paste it has the potential to be carbonated prior to re-use in order not only to store CO2, but also to enhance its reactivity. In this study, a concrete waste slurry obtained at a ready-mix concrete plant was investigated. For accelerated carbonation, a wet process in laboratory scale was used. The carbonated product was dried afterwards, characterized and used as supplementary cementitious material. When carbonated, the hydrate phases of the concrete waste slurry decomposed to calcite, gypsum and a silica-alumina gel. When blended with Portland cement (30% replacement by mass) early hydration kinetics was accelerated by the carbonated concrete slurry waste. The pozzolanic reaction of the silica-alumina gel consumed a significant part of the portlandite and showed a positive contribution to compressive strength compared to inert quartz powder and to the uncarbonated concrete slurry.

Frank Winnefeld, Johannes Tiefenthaler, Andreas Leemann
Accelerated Carbonation of Recycled Concrete Aggregates and Model Materials

The accelerated carbonation of recycled concrete aggregates (RCA) has been suggested to improve their properties. Several physical and mechanical phenomena occur during the carbonation of adhered cement mortar, but the relationship between bound CO2 content and the variation of RCA properties is not clear. In this study RCA and model materials (spheres) have been exposed to carbonation, and then characterized at different times to monitor the evolution of their macroscopic properties (porosity and absorption kinetics) as a function of their carbonation degree. A decrease in porosity and saturation rate was actually observed for models materials whereas the initial natural carbonation of industrial RCA limited the storage of CO2 and consequently the evolution of their properties.

Farah Kaddah, Ouali Amiri, Harifidy Ranaivomanana, Emmanuel Roziere
Direct Aqueous Mineralization of Industrial Waste for the Production of Carbonated Supplementary Cementitious Materials

In the steelmaking process, electric arc furnace (EAF) is regarded as a green production route, as it essentially uses ferrous scraps instead of virgin raw materials. In addition, the alkaline composition of the slag derived from the EAF production makes it suitable for carbonation treatment, and specifically for the permanent storage of CO2 through the implementation of the mineralization process. Therefore, in this study, EAF slag carbonation is performed in a slurry configuration, at room temperature and ambient pressure, in order to assess the CO2 storage potential under minimized energy consumption conditions. Specifically, the slurry was prepared at a liquid-to-solid ratio of 3; CO2 with a partial pressure of 99.9% was fluxed into the slurry at 25 ℃ under the pressure of 1 bar with a flowrate of 150 L/h, and reaction time of 1 h. Moreover, in order to investigate the reproducibility of the mineralization process, three tests under the same conditions were replicated. The carbonation efficiency was estimated to be around 32%, and the results achieved were compared to previous literature studies. This research confirms that direct aqueous carbonation is a valuable method for inducing mineralization in powdered materials. Future investigations will be aimed at assessing the potential of the carbonated slag to act as supplementary cementitious material by partially substituting clinker binders in cement-based manufacts.

Francesca Bonfante, Giuseppe Ferrara, Pedro Humbert, Jean-Marc Tulliani, Paola Palmero
Performance and Hydration of Composite Cements with Carbonated, Recycled Concrete Paste

Hydration reactions and performance evolution of composite cements containing carbonated recycled concrete paste (cRCP) as a new supplementary cementitious material are investigated. The focus is on the effect of the origin of the concrete paste and type of cement clinker used to produce the composite cement.Alumina-silica gel being the main component of the carbonated paste is characterized by the pozzolanic properties. The rate of the pozzolanic reaction is very high. Already after one day, a high reaction was achieved followed by a close to complete reaction of the carbonated paste within 28 days under the conditions applied in this study. The fine microstructure formed in the presence of the cRCP results in a significant increase of the compressive strength. The initial characteristics of the paste are determining the content of the carbonatable material, content of the gel formed and finally its impact on the hydration and evolution of the mechanical performance. The mechanisms of reaction are independent of the characteristics. The characteristics of the cement clinker impact the reaction and the effect of CRP on performance evolution to a limited extend.

Maciej Zajac, Jørgen Skibsted, Patrick Ullrich, Jan Skocek, Mohsen Ben Haha
Potential of CO2-Storage in Recycled Concrete Aggregates by Accelerated Carbonation

To reduce the carbon footprint of cementitious materials and resource extraction intensity of concrete industry (natural gravel or crushed rock), usage of recycled concrete aggregate (RCA) in concrete and as a CO2-sink by accelerated carbonation is widely investigated. Implementation of this technology will not only reduce the climate impact, but also improve the performance of the RCA creating a truly circular material. At first, some locally available recycled concrete was crushed in different fractions and characterized. To quantify the adhered mortar/aggregate content ratio on the as-received RCA, an image analysis method (IAM) was introduced. The analysis revealed that the adhered mortar accounts for around 40% of the RCA independently on the fraction. The results of IAM of as-received RCA were used to evaluate its remaining potential of CO2-storage. The effect of accelerated carbonation on the quality of RCA was evaluated by means of water absorption. The carbonation was determined by means of thermogravimetric analyses (TGA) and its derivative curve (DTG) resulting in similar CO2-storage for coarse fractions 4/8 mm and 8/16 mm under the accelerated carbonation conditions.

Alexander Oliva Rivera, Jan Suchorzewski, Katarina Malaga
Effect of Selected Process Parameters During Carbonation Hardening on the CO2-Binding Potential of Cementitious Materials

The cement industry faces an urgent challenge to reduce CO2-emissions. A promising technology to bind CO2 permanently in cementitious systems is Carbon Capture and Utilization (CCU). Carbonation hardening represents one approach of CCU technologies, and consists of the following steps: pre-curing, carbonation curing and post-curing. The process parameters at each step affect the carbonation degree and rate.During carbonation curing, combined hydration and carbonation reactions take place. This includes the formation of hydrates as well as carbonates of anhydrous clinker minerals. These reactions proceed simultaneously and are difficult to separate. Therefore, to get a deeper insight into these reactions and to control them, the process parameters that affect the carbonation reaction need to be investigated. Particular interest is ascribed to the relative humidity (RH) in the system as this considerably affects the carbonation degree, since CO2 needs to dissolve in water to react with the calcium from the cementitious phases.This study investigates the effect of selected process parameters during the pre- and carbonation curing on the CO2-binding potential of cementitious systems. For this, cement pastes were prepared and pre-cured for 6 h or 12 h at 30–80% RH. The carbonation curing was performed in a CO2 chamber at a CO2 concentration of 50% for different durations at 50% RH. The carbonate and bound water content in the samples were quantified with thermogravimetric analysis (TGA).The results of this study will help elucidating the carbonation hardening mechanism and act as a basis for applying CCU on cementitious materials.

Elena Woydich, Anne Heisig, Harald Hilbig, Alisa Machner
Two-Step Carbonation of Pervious Concrete Prepared with Recycled Concrete Aggregates: Aggregate Property, Experimental Setup and Preliminary Results

To reduce the carbon footprint of cement and concrete industry, CO2 curing has been recognized as one of the sufficient ways. However, the amount of CO2 uptake by the normal structural concrete is limited because of their low permeability. Compared to curing the traditional concrete members, CO2 curing of pervious concrete is expected to sequester more CO2 due to the well-connected pore network and high permeability. In addition, studies on the effective utilization of resources found that the carbonation of recycled concrete aggregates (RCAs) prepared from the demolition building waste can improve the bonding between RCAs and the cement matrix. In this study, we propose to combine two carbonation steps (carbonation of RCAs and carbonation of precast pervious concrete) together to improve concrete quality and maximize CO2 sequestration in carbonated concrete. The preliminary experimental results show that the amount of CO2 captured by the carbonated pervious concrete with carbonated RCAs is higher than the normal concrete. Compared with non-carbonated RCAs, the strength of concrete with carbonated RCAs is improved. These results prove to a certain degree that the way of using the carbonation method to massively produce the precast pervious concrete is a feasible approach to mitigate carbon footprint of cement industry without scarifying the property of pervious concrete.

Zhidong Zhang, Xiulin Chen, Ueli Angst

Digital Approaches to Structural Concrete

Development of an Innovative 3D-Printing Process for Reinforced Concrete – AMoRC Method

In this paper, a novel 3D printing process for reinforced concrete structures called Additive Manufacturing of Reinforced Concrete (AMoRC) is proposed. The process consists of a continuous concrete extrusion process and an intermittent stud welding process, both carried out by a robotic arm respectively. The welding robot runs ahead of the concrete extrusion robot and produces the spatial reinforcement mesh from prefabricated reinforcing bar segments. A novel fork-shaped print head with four adjustable nozzles allows for concrete extrusion around the reinforcement with different diameters. By joining segmented rebars of limited length to a reinforcement mesh in the AMoRC process, the consumption of energy and time can drastically be reduced compared to shape welding. The length of the joined rebars can be adapted to the component geometry and the extrusion speed. The bar segments to be joined are kept ready in a magazine belonging to the print head, which enables the feeding of bars with different diameters to arrange a load-efficient and economical reinforcement mesh. The preliminary testing of the additively fabricated reinforced concrete components is also implemented to characterize the structural behaviour of those 3D-printed composite specimens. In the initial phase, the reinforcement installation was performed manually until the second robot will be added to the process and experiments were done to characterize the printed structures. The pull-out test is used to investigate the bonding behavior between reinforcement and printed concrete. The four-point bending test is also utilized to study the mechanical behavior of the printed reinforced concrete specimen in a larger scale.

Sisi Zhang, Matthias Kalus, Sven Engel, Josef Hegger, Martin Claßen
Investigations to Improve the Carbon Footprint of Thin Walled Concrete Structures by 3D Printing Prefabricated Elements

Additive Manufacturing - AM processes are gaining acceptance in many industries due to their unique design freedom. New design approaches such as topology optimization (TO) and structural optimization using lattice structures are possible. Pilot projects in the housing industry show that possible applications, in this case concrete AM, are also conceivable in the context of construction processes. This paper deals with the production of thin-walled concrete structures and shows material-related reduction potentials compared to conventional prefabricated concrete components. To this end, various extrudable high-performance mortars, some with fiber admixtures, have been developed and an appropriate standardised test specimen has been designed. On the basis of numerous material tests, it was possible to derive significant statements about the application limits of the developed materials, which are fundamental for the design of topo-logically optimised cross-sections of concrete components. The aim of this research project in the field of concrete AM is to produce segmentally built flexural beams and to investigate their load-bearing capacity. The test beams consist of several segments, each with a concrete formulation and a 3D design adapted to its calculated stresses. The segments themselves are manufactured without any classical reinforcement elements and are joined together after the manufacturing process with the application of prestressing with or without subsequent bonding. The segments can also be CO2 cured in an accelerated process prior to prestressing to further improve the material properties and to further reduce the environmental footprint through CO2 storage.

Marc-Patrick Pfleger, Sebastian Geyer, Christian Hölzl, Markus Vill
An Optimum Mix Design Method for 3D Concrete Printing Applications

Developing cement-based mortar mixes for three-dimensional printing applications is a challenging task with multiple competing objectives, especially with climate change adaptation. Mortar mix design is a laboratory method that determines the necessary quantities and types of cement, sand, chemical admixtures, and water to form a combination with the specified qualities. The influx of new ingredients to investigate can lead to an inefficient amount of labour. This research is part of a bigger project aiming to automate the development of mortar mixtures for three-dimensional concrete printing technology. A party optimizer suggests novel combinations by adjusting the ingredients and their proportions, whereas feed-forward neural networks predict their properties. In total, seven factors are investigated, five of which are quantitative and two qualitative. These factors include the type of cement and superplasticizer used, as well as the sand-to-binder ratio, water-to-binder ratio, and admixture doses. The initial set of mixes formed in the laboratory derived from a D-optimal set of 18 mixes. Tests frequently used in traditional construction are conducted to correlate them with important properties for 3D concrete printing applications. The flow table test correlates with flowability, whereas the slump test correlates with shape stability. The mixtures with the desired properties are then tested with the extrusion system, which includes a progressive cavity pump and an extrusion head. This is an ongoing study also including lower carbon mixes and it is expected that as the number of iterations increases, so will the qualities of the mixtures according to the given design criteria.

Vasileios Sergis, Claudiane Ouellet-Plamondon
3BUILD – First 3D Printed Structure in Greece

Digital fabrication, including construction of buildings with use of 3D printers is gaining significant momentum for the construction sector. Benefits such as free form architecture, reduction of building time, labor costs and waste material, freedom of geometry can be taken advantage in such building techniques. 3D Printing Concrete (3DCP) is a wet manufacturing process where layers of extruded mortar are bound by successive material deposition. Most common equipment for this type of application are the gantry printers, which are based on the cartesian robotic systems technology. 3BUILD is the research project, co-funded by the “Ereyno-Dimiourgo-Kainotomo” program by the Greek Ministry of Development, with participation from TITAN, SIKA, COS and NTUA. The project main objective is the design and construction of a gantry type 3D printer and furthermore the use of the printer for the construction of a structure of dimensions up to 8 × 8 × 3 m. Development of works for the certain project included the design and construction of a middle-sized printer and printing of 2 m high structures of various shapes, investigation of sensitivities of mortar properties to different printing parameters (printing speed, printing geometry, layer dimensions) and relevant adjustments, the design and final construction of the full scale 3D printer and all challenges encountered and resolved before finally printing in real scale.

Marios Katsiotis, Vasileios K. Michalis, Despoina Papargyriou, Emmanouil Mavratzotis, Martha Savvidou, Theodoros Mavrelos, Despoina Almpani, Ioannis Tsilikas, Christos Kalligeros, Georgios Vasileiou, Dimitrios Papageorgiou, Athina Stavridou, Vasilios Spitas
Natural Fibers for a 3D Printable eco-ECC Material

In recent years, the conventional construction sector has been noted for its low productivity, as well as being a major generator of CO2 emissions and waste. Faced with this problem, 3D printing has positioned itself as an alternative since, due to a lower consumption of materials, as well as a reduction for waste. Therefore, in recent years, interest in cement-based material for 3D printing has increased in the construction sector as a partial or total replacement for conventional construction methods. Numerous materials have been developed to meet the requirements of 3D printing, such as geopolymers or Engineered Cementitious Composites (ECC). ECC has the capacity for autogenous self-healing, that is, the material presents in its composition the capacity to reduce and heal the possible cracks that are generated. In this study, the focus has been on the development of an ECC material that has the characteristics to achieve structural integrity, reliability, and robustness of 3D printing (A3D_ECC). The main goal of this study is the design and development of a self-healing and efficient eco-cement-based material (eco-A3D_ECC).The substitution of synthetic fibers (PVA) by natural fibers, spruce, reaches an eco-ECC, eco-A3D_ECC. Fresh properties of the A3D_ECC and eco-A3D_ECC materials are evaluated by consistency, open time, extrudability, and buildability. Hardened properties are researched via compressive and flexural strength for up to 90 days. Meanwhile, the self-healing behavior of A3D_ECC and eco-A3D_ECC is investigated by mechanical recovery test, and absorption and sorptivity tests. For these methods, specimens are cured at room temperature 34 ± 2% RH and 20 ± 2 °C.This study presents the results of the tests in the fresh and hardened state to know the influence of the natural fibers in the material properties in comparison to synthetic ones. In addition, the research describes the experimental study and also shows the results that confirm the autogenous healing of eco-A3D_ECC when natural fibers are used.

Fernando Fernández, Rocío Jarabo, Eloy Asensio, Ana Guerrero
Performance of Data Driven Algorithms to Predict Concrete Strength Using Production Raw Data

Predicting properties of concrete is a major issue for building sustainable structures. In the last decade, numerous publications have shown that machine learning algorithms can play a major role to predict these properties. The key factor is the availability of data to train the models. Collecting, cleaning and consolidating data can be challenging tasks, especially in a concrete industry in which the digitalization of the supply chain is still in progress. We propose in this study to use raw production data to evaluate the performance of a machine learning algorithm compared to an empirical model. The concrete strength value is predicted using both approaches and compared to the measured value. Even if machine learning algorithm shows good performance, no significant increase in the prediction accuracy is obtained.

Arnaud Delaplace, Ulli Olivetti Razinhas, Régis Bouchard, Andreas Griesser
Prediction of Mechanical Properties of Steel Fibre-Reinforced Self-compacting Concrete by Machine Learning Algorithms

With the development of big data processing technology and the continuous improvement of computer operation ability, machine learning has achieved remarkable results in recent years. Applying machine learning to solve engineering problems is gaining more attention from researchers. Steel fibre-reinforced self-compacting concrete (SFRSCC) is a new type of composite material prepared by combining the advantages of the high fluidity of self-compacting concrete (SCC) and the high toughness of steel fibre-reinforced concrete. However, the performance of SFRSCC is influenced by many factors such as water-binder ratio, mineral powder content and steel fibre content. This study aims to predict the mechanical properties of SFRSCC mixes based on datasets collected from the literature. In the presented work, the machine learning algorithms are employed to investigate the effect of SCC compositions and steel fibre on the performance of SFRSCC. The models used for the prediction are support vector regression (SVR) and artificial neural network (ANN). In both models, input variables are set to be water to binder ratio, sand to aggregate ratio, maximum size of coarse aggregate, amount of other mix components (e.g., superplasticizers, limestone powder, fly ash), volume fraction and aspect ratio of steel fibre, and curing age. The output variables are flexural strength and compressive strength of SFRSCC specimens. The performances of machine learning models are evaluated by comparing the predicted results with experimental results obtained from the literature. Furthermore, a comparative study is performed to select the best-proposed model with better accuracy.

Tianyi Cui, Sivakumar Kulasegaram, Haijiang Li
Generalization Capability in Machine Learning Approaches for Hammering Test Method

Hammering test method is widely used as a method for detecting internal cracks or flaking of concrete caused by corrosion of reinforcing bars in concrete structures. However, the problem is the variation of accuracy because it depends on the skill of the inspection technician. The authors try to apply Machine Learning to make it accurate, stabilize and automate the Hammering test. Based on the hammering sound data obtained on site, the change in sound due to internal cracks in concrete appears in the characteristics of the scalogram. Convolutional Neural Networks (CNN) are specialized machine learning method to classify the characteristics of images. CNN will classify the change of scalogram caused by the deterioration of concrete, but the specific network may not be always effective in different site. To obtain a generalization capability, the authors proposed to use the CNN as a feature extractor. To evaluate the difference of the feature vectors between normal and defect, Mahalanobis’ Distance were adopted. This method showed good generalization performance on several sites with different conditions.

Shimbo Hiroshi, Mizobuchi Toshiaki, Ozeki Tomoko, Nojima Jun-Ichiro, Sano Shunsuke, Okamoto Masafumi, Shizuno Tomohiro
Comparison of Machine Learning Algorithms for the Prediction of the External Sulphate Attack Resistance of Blended Cements

Using supplementary cementitious materials (SCM) can help increase the sulphate resistance of cement blends. However, formulating sulphate-resistant materials with increasing amounts of SCM is challenging, and the required standard tests last several months. Therefore, creating new tools that can be easily applied and understandable could help develop novel materials in the future. Machine learning techniques have been widely used recently to predict cementitious materials’ properties such as strength, creep, or shrinkage. However, their usage is relatively limited regarding durability properties, maybe because of the large number of parameters involved in durability processes, some of them intrinsic to the material and others related to the environment. In this study, an extensive database has been built using more than 300 cementitious sample characteristics from different studies. A large collection of inputs related to cement composition, mix composition, sample geometry, and environmental conditions such as sulphate concentration has been gathered. Then several machine learning algorithms were applied to assess the resistance of blended cements to the external sulphate attack. Two groups of algorithms, e.g., classification and Regression algorithms, incorporating several models from linear to ensemble models, have then been compared. The results show that most classification models can very quickly assess the sulphate resistance of cementitious materials using the extensive database, and the best Regression models can efficiently predict the temporal evolution of the degradation. The most influential parameters can be identified, and recommendations can be drawn regarding future blended cement compositions.

Abdelhamid Hafidi, Benoit Hilloulin, Sonia Boudache, Umunnakwe Rejoice, Ahmed Loukili

Durability and Robustness of Concrete Materials and Structures

Leaching Characteristics of Cs from the Decomposed Cu Ferrocyanide Adsorbent Solidified by Portland Cement and Geopolymer

The use of cement technology is under investigation for the disposal of 137Cs, which is a type of radioactive waste and which was dispersed as a result of the accident. Here, we present the results of a study on the leaching characteristics of Cs from solidified bodies. Combustible materials contaminated with radioactive Cs released by the accident at the TEPCO's Fukushima Daiichi NPS are incinerated to reduce their volume, and the incineration residue is further reduced by melting treatment. Cs exists as water-soluble salts in the molten fly ash. The Cs can be transferred to the liquid phase by washing, and the Cs can be further concentrated by ion-exchange chromatography using Cs adsorbents such as ferrocyanide transition metal salts. The adsorbent used must be stabilized for final disposal. We present an example of using copper ferrocyanide as an adsorbent in this process. Copper ferrocyanide was calcined and decomposed, then solidified with Portland cement or metakaolin geopolymer. Since cement hydrate has no cation exchange property, all Cs leached into pure water, but copper ferrocyanide, after pyrolysis, became cation exchangeable in the alkaline environment of Portland cement, resulting in a Cs leaching rate of only 20%. The Cs leaching rate from the geopolymer solidified body was 2% because the geopolymer is an ion exchanger and has a large Cs ion selectivity for Na ions. However, from the viewpoint of workability during mixing, there was an upper limit to the amount of material to be treated, and cement solidification was superior in terms of volume reduction.

Kazuo Yamada, Tsuneki Ichikawa, Yasumasa Tojo, Kazuto Endo
Development of High-Performance Fiber-Reinforced Cementitious Composite (HPFRCC) Using Titanium Dioxide and Nylon Fiber

This study attempted to develop high-performance fiber-reinforced cementitious composite (HPFRCC) achieving excellent mechanical properties and nitrogen oxide removal capacity by using photocatalyst and nylon fiber. Titanium dioxide, which has a particle size similar to those of materials typically used in cementitious composites, was utilized as a photocatalytic material. Two different types of titanium dioxide (NP-600 and GST) were used, and changes in microstructure and mechanical performance were observed by adjusting the mixing ratio and treatment methods. Analyses microstructure and chemical composition, nitrogen oxide removal tests, and mechanical tests were conducted sequentially, and the series of experimental processes were repeated if necessary. It was confirmed that an increase in the incorporating rate of titanium dioxide allows higher titanium component measured on the surface of the cementitious composite, which also had a positive effect on the improvement of nitrogen oxide removal capacity. However, an increase in titanium dioxide content negatively affected mechanical performance by reducing flow length and workability. Workability of composites decreases dramatically when titanium dioxide replaces silica flour by more than 80%, which caused problems in the mixing and depositing process. On the other hand, the superb mechanical performance could be achieved when the corresponding ratio was 75%. The incorporation of nylon fibers showed a similar effect to that of polymer fibers in terms of enhancing compressive strength and flexural strength. However, the nylon fiber did not provide sufficient ductility to the cementitious composite.

Hong-Joon Choi, Soonho Kim, Taekgeun Oh, Rongzhen Piao, Doo-yeol Yoo
Rheology, Mechanical Properties and Durability of Self-compacting Concrete Using Sustainable Expanded Perlite Microspheres

The partial replacement of a conventional limestone filler with sustainable perlite microspheres was investigated in the present study, by examining its effect on rheology, physical characteristics, mechanical properties and durability of Self-Compacting Concrete (SCC). Expanded perlite microspheres (EP) were produced after thermal treatment of the ultra-fine content of Residual of Perlite Mining (RoM), using an innovative technology of vertical electric furnace and achieving the desired expansion by precisely adjusting the heating temperature and the heating time. Its high sphericity in conjunction with low open porosity system compared to conventional expanded perlite powder, can highly contribute to SCC production of excellent rheological behavior without any segregation signs, even by significantly increasing the water content. In addition to the above and unlike the traditional fine filler materials, the EP incorporation results in chemical admixture reduction which in turns leads to concrete compositions of lower cost and higher sustainability indices. The results after a series of tests regarding physical characteristics, mechanical properties and durability, indicated the beneficial role of perlite microspheres. Among others, special mention should be made of the EP addition positive effect on the late compressive strength development, drying shrinkage, freeze & thaw and fire resistance of the EP-SCC mixtures.

Andreas Kounadis, Efstratios Badogiannis, Panagiotis Angelopoulos, Dimitrios Petrakis, Vasilios-Orfeas Tsiaras
Length Change and Water Uptake Characteristics of Synthesized Calcium Silicate Hydrates

Length change of cement based materials due to drying and wetting has been classically studied and various mechanisms have been proposed. Recently, it was reported that the structural change of amorphous calcium silica hydrates (C-S-H), especially, by drying at low relative humidity, can greatly affect macroscopic shrinkage and irreversible behavior. In addition, it has been pointed out that the water transport in the dried cement based materials can be influenced by the C-S-H swelling due to the wetting to cause anomalous water uptake. In this study, the length change and water uptake of synthesized calcium silica hydrates powder and commercial porous materials with tobermorite or xonotlite are examined focusing on the effect of crystalline structural change due to drying and wetting. The powder was compacted to be used for length change. It was found that there is no hysteresis even at low relative humidity in the case of tobermorite and xonotlite with well-ordered structures and the unique expansion with drying was found at high relative humidity. The water uptake amount in the porous materials mainly consisting of tobermorite or xonotlite is almost proportional to square root of time to satisfy Washburn’s theory. The secondary imbibition period was slightly observed only in porous materials containing tobermorite like cement paste. It may be attributed to the slow water penetration into the layer structure of tobermorite. The characteristics of water uptake in the materials compacted by synthesized C-S-H powder is dependent on CaO/SiO2 mole ratio.

Shingo Asamoto, Rintaro Koyama, Kunio Matsui, Keisuke Takahashi
Development of a Framework to Provide Concrete with a Low Carbon Footprint and Enhanced Resistance Against ASR-Induced Development

The concrete industry needs to find cost-effective technologies to reduce the carbon footprint of its products. At the same time, these technologies should not reduce the concrete performance, including long-term durability. The great demand for concrete and the expected shortages of high-quality aggregates (e.g., ASR resistant) in the coming years will enhance the probability of using inferior raw materials that will reduce the lifespan of concrete infrastructures. This study aims to develop a new approach taking the chemical composition of the binder into account for the concrete mix-design toward the mitigation of ASR, while reducing the carbon footprint and cost of concrete. In this work, blended cements that fall into the “safe” combination of CaO, SiO2, and Al2O3 (main oxides in cementitious materials) with regard to ASR were tested for their mechanical properties and resistance to expansion upon ASR. The data gathered demonstrate promising results on using the proposed ternary oxides approach: by comparing the effect of the different portions of Al2O3, SiO2, and CaO it was demonstrated that the higher the content of either Al2O3, SiO2, or both, the lower ASR-induced expansion development. Yet, keeping the amount of CaO constant, the results suggest that mixtures with a higher amount of SiO2 than Al2O3 tend to be more efficient in mitigating ASR. The results provide interesting data to help in the decision making to select the best options (i.e., the combination of different SCMs and their quantities) to apply in concrete structures exposed to ASR development.

Diego Jesus De Souza, Anne Heisig, Alisa Machner, Wolfgang Kunther, Leandro Sanchez
Evolution of Air Permeability of Concrete due to Expansion Caused by Internal Swelling Reactions (ISR)

Predicting and evaluating the transfer properties of concrete affected by Internal Swelling Reactions (ISR) is a main challenge for experts involved in concrete durability testing. The aim of this study is to measure the evolution of air permeability with the development of ISR, for different levels of expansion and various degrees of concrete saturation. In this work, two ISR were studied: the Alkali-Silica Reaction (ASR) where the origin of the swelling is located in the aggregates, and the Delayed Ettringite Formation (DEF) where the origin is located in the cement matrix. The first results obtained show that the development of ISR and induced cracks leads to an increase in the air permeability of concrete, especially in highly saturated concrete. The data of this study make it possible to evaluate the evolution of the transfer properties according to the generated expansion and induced cracking and the degree of saturation of the concrete.

Joe Maalouf, Hugo Cagnon, Jérôme Verdier, Jacques Jabbour, Stéphane Multon
The Effect of Heat Curing on the Early-Strength Development of Low-Carbon Concrete

The production of cement clinker requires the heating of raw materials up to a temperature of 1450 ℃, making it the third largest industrial energy consumer, generating 6–7% of global CO2 emissions. The fastest alternative for reducing the environmental impact of the cement industry is the partial replacement of cement clinker with supplementary cementitious materials (SCM). Due to the high price of silica fume and the sharp decrease in fly ash, ground granulated blast furnace slag seems the most promising SCM for the latter purpose. However, the high level of cement clinker substitution with slag can delay the setting and hardening time of low-carbon concrete.In the scope of this study, heating cables are applied to investigate the effect of heat treatment on the early-strength development of low-carbon concrete. The heating cables are used to supply enough energy to the slag grains and activate their hydration. The amount of heating energy, starting time and duration of heating are tested to accelerate the hardening time of cement with 40–70% of slag to the same level as cement with around 20% of slag (CEMII/B), which is the most used in Finland. Also, the optimum curing process with the least demand for electricity is estimated. The heating system was developed to uniformly distribute the defined amount of heat inside the cast samples. The experimental methods applied to evaluate the development of compressive strength included tracking of the ultrasound pulse velocity, rebound hammer and continuous temperature measurement.

Anna Antonova, Ekaterina Illarionova, Fahim Al-Neshawy, Jouni Punkki
PVME as a Sustainable Alternative to Improve Performance of Dense Mortar at Elevated Temperature

The exceptional strength and durability make High strength concrete (HSC) an ideal material for application in shear walls, tall buildings and offshore structures. There have been concerns about using HSC under fire conditions, particularly due to the possibility of explosive spalling. Polypropylene (PP) fibre has shown to mitigate spalling in concrete. Polypropylene is a thermoplastic fiber which is composed of hydrocarbons and is extracted from fossil fuels. The production of PP fibre releases toxic chemicals in the environment and is non-biodegradable, hence sustain in our biosphere for several years and thus contribute towards the ever-increasing air and water pollution. When mixed in concrete, PP fibres negatively impact the workability and can result in non-homogeneous mixes because the fibres agglomerate during compaction. Polyvinyl methyl ether (PVME) is a water-soluble polymer which can be sustainably synthesized from biomass and its addition to HSC can be a creative approach to prevent spalling in fire-related situations. The present work investigates the influence of PVME on its pore creation ability and mechanism in mortars at elevated temperature. PVME demonstrated pore formation capabilities in mortars at high temperature, which was found to be similar to that of PP fibre modified mortars. The volume of interconnected pores increased as a result of PVME addition, which allows gases and moisture to escape and reduce spalling during the event of a fire. The current work proposes a more sustainable alternative to improve the fire performance of HSC.

Vikash Kumar Singh, Gaurav Srivastava
Evaluation of the Correlation Between ASR Expansion and Pozzolanic Reactivity of Ternary Concrete Systems Containing Glass Powder

Glass powder (GP), as supplementary cementing materials (SCMs) in concrete manufacturing, is characterized by two controversial facts. Post-consumer GP is mostly made of silica in an amorphous phase, which provides high pozzolanic reactivity potential. However, its high alkali content (≈13% Na2Oeq) has a negative effect on concrete expansion by engaging alkali-silica reactions (ASR), which differentiates GP from other conventional SCMs. Both perspectives are the subject of multiple debates concerning the possibility of alkali release into the concrete pore solution over the long term. As well as how the synergistic combinations of GP and other SCMs could be the key to this issue. The combined use of GP and other SCM with higher silica/alumina contents offers a promising alternative to reduce the expansion of concrete to the normative lower limits. In this context, this paper focuses on studying the mechanism that prevails by linking the expansion of binary and ternary concrete and the pozzolanic reactivity of the respective GP/SCM blends by isothermal calorimetry based on the R3 method. All to establish a potential dosage that will allow the broad use of GP as SCM. The expansion of concrete prisms made with reactive aggregates and different percentages of GP and metakaolin, silica fume, fly ash or blast furnace slag was measured for over 6 years. The synergy was observed in specific blends, as the GP/metakaolin and GP/silica fume samples systematically decreased concrete expansion in comparison with the binary prisms. Accordingly, calorimetry results reported an increased reactivity for the same systems, showing a wide correlation within both parameters.

Wena de Nazaré Do Rosário Martel, Josée Duchesne, Benoit Fournier
Experimental Investigation on the Novel Self-healing Properties of Concrete Mixed with Commercial Bacteria-Based Healing Agent and Crystalline Admixtures

Repairing the cracks in concrete structures is relatively difficult and the manual repair techniques are costly and time-consuming. To overcome this obstacle, stimulated autogenous and autonomous self-healing technologies offer a potential benefit. The healing agents are normally added in the concrete during casting. In fact, traditional concrete also has an autogenous healing ability but the self-healing effect is rather limited. In this study, self-healing concretes were made with two commercial healing agents, namely bacteria-based healing agent (BAC) and crystalline admixtures (CA). The fresh and mechanical properties of concrete were initially evaluated. The addition of healing agents increased the 28 d compressive strength of concrete by 4% for CA and 16% for BAC. The self-healing properties of concrete were evaluated by two methods: (1) crack closure measurements by means of optical microscopy and (2) water flow tests by use of the permeability setup. Results showed that the addition of healing agents showed an advanced progress of the crack closure with increasing healing time, and the permeability rate considerably decreased as a result of the crack clogging by healing products. The self-healing concretes showed better healing and sealing efficiencies than the autogenous self-healing in the traditional concrete, showing a promising result to apply the agents in real applications.

Harry Hermawan, Virginie Wiktor, Pedro Serna, Elke Gruyaert
Incorporation of Hybrid Biopolymer/Silicate-Based Microcapsules in Cementitious Mixtures for Potential Uses in Self-healing Technology with Renewable Materials

The high demand for cement for repairing concrete structures leads to adverse environmental impacts, reducing the cement industry’s sustainability. For that reason, using renewable materials to develop self-healing cement-based materials is desirable to diminish cement consumption for rehabilitation and increase the durability and reliability of concrete structures. Evaluation of hybrid organic/inorganic microcapsules for autonomous self-healing of cementitious materials offers a solution for microcracking, meanwhile conferring better characteristics to construction materials. Microcapsules evaluated in this study with a core of Silicate-based (MC-SS) and Biopolymer/Silicate-based (MC-SS-St) resins covered by a Silica shell were synthesized and added in replacement of microsilica in cement pastes at a dosage of 2.5, 5.0 and 7.5% by weight of cement. The microcapsules and microsilica were characterized by XRD, SEM, and FTIR. Performance of cement pastes with microcapsules addition was followed by flexural and compressive strength of prismatic specimens of 1 × 1 × 6 cm3 at 7 and 28 days of curing immersed in water at room temperature. Total porosity was followed by MIP at 28 days of curing. Also, the workability of samples with 2.5% microcapsules was compared with a cement reference mixture (CEM I) and cement with microsilica (MS) as the blank sample. Obtained results show differences in the morphology of microcapsules compared with microsilica. Moreover, as was expected, the water/binder ratio (w/b) increases with microcapsules addition, which reduces mechanical resistance. However, with the higher substitution of microcapsules, the obtained values accomplish the current regulations. Therefore, the proposed microcapsule-based system under evaluation is a promising product designed for self-healing cementitious mixtures.

Sandra Arroyave, Eloy Asensio, Jairo E. Perilla, Paulo César Narváez-Rincón, Albeiro Cadavid, Ana Guerrero
Towards Development of Sustainable Ultra High Performance Fiber Reinforced Concrete (UHPFRC)

Climate change is one of the main problems that our planet faces. A challenging issue in the Civil Engineering field is to produce more sustainable materials and structures. Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is cementitious material with advantageous mechanical properties. UHPFRC can be used in a number of applications that require high-strength, ductility and durability. In the production of UHPFRC large quantities of cement, aggregates and steel fibers are required. In this investigation, Ground Granulated Blast Furnace Slag (GGBS) has been used as partial replacement of cement to produce a more sustainable UHPFRC. In addition, general purpose unprocessed recycled steel fibers have been used as an alternative to conventional new steel fibers. A comparison is made of the different types of fibers used. The results of the present study indicated that the compressive strength of HPFRC is not affected significantly for GGBS contents up to 30%. The addition of unprocessed recycled steel fibers resulted in an increase in the compressive strength of UHPFRC. In tension, the UHPFRC material presented strain softening and with an overall lower strength compared to using conventional fibers. As long fibers tend to become entangled, in the present study short recycled fibers have been used. Further study is required to investigate the use of suitably treated recycled fibers of various lengths.

Spyridon A. Paschalis, Andreas P. Lampropoulos, Joseph P. Rizzuto
Investigation of the Mechanical Properties and Durability of Concretes Produced with Microsilica and Crystalline Admixtures

In order to enhance the durability of reinforced concrete structures and their protection against corrosion, the addition of various durability enhancing concrete admixtures to the composition of the mixtures is a catalytic factor, in addition to proper concrete mix design and correct execution of the concreting process. This durability enhancing concrete admixtures include permeability reducing admixtures, such as crystalline admixtures, as well as silica fume (microsilica). Crystalline admixtures reduce permeability, which is one of the key factors leading to premature concrete wear and corrosion of the reinforcement, sealing capillary pores and cracks through the crystal growth mechanism under the presence of moisture. Correspondingly, microsilica as a strong pozzolanic material has the ability to reduce porosity and create a denser structure in hardened concrete, acting equally beneficial on long-term durability. The durability testing of the specimens of the first experimental part was carried out through appropriate laboratory tests involving the determination of the compressive strength of each mixture, the depth of penetration of water under pressure and the deterioration of concrete, either due to carbonation or due to chloride ingress. Results indicate that addition of crystalline admixture enhances the durability of concrete against carbonation and chloride induced corrosion. These durability indicators are further enhanced when crystalline admixtures are used in combination with silica fume.

Kosmas K. Sideris, Eirini Mingou, Christina Solomou
A New Class of Hybrid Self-healing Cementitious Materials Combining Shape Memory Alloy Wires and Super Absorbent Polymers

It is anticipated that deterioration of concrete infrastructure around the world will be exacerbated as changes in our climate becomes increasingly uncertain. As a result, enormous economic investments are being made each year to repair concrete structures to both maintain and extend their service lives. Thus, the development of more intrinsically resilient concrete materials is needed more than ever. This research focuses on developing a new hybrid self-healing cementitious material which leverages the characteristics of shape memory alloy (SMA) wires and super absorbent polymers (SAPs). SAPs have the ability to absorb very large amounts of water. When added during batching of cementitious materials, SAPs can absorb water from the surrounding environment which enhances the material’s ability to autogenously seal cracks and recover a portion of its original mechanical properties. However, this autogenous healing mechanism has been shown to only be effective for sealing relatively small cracks. This experimental study proposes using SAPs in combination with SMA wires which, when heated, can recover their original shape, and simultaneously reduce cracks to widths which can be sealed through enhanced autonomous self-healing. To evaluate this new hybrid mechanism, the concept of ‘self-healing efficiency’ is defined and investigated through microscopic measurement of crack widths, and the experimental measurement of fracture energy recovery. The results revealed that for specimens containing SAPs and subjected to cyclic curing, 41% of crack widths were completely sealed after 28 days, and 1.54 fracture energy recovery was achieved. The results of this study are promising and have demonstrated the efficacy of this new hybrid healing mechanism and its potential to create longer lasting and more resilient concrete infrastructure.

Mario Antoun, Liam J. Butler
Carbonation or Chloride Ingress? Which One is the Durability Key Factor in Low Reactivity Clay and Limestone Blended Concrete

As Portland cement production is responsible for 0.8 ton of CO2 for 1 ton of clinker produced, there is currently a strong global pressure to reduce its production in order to decrease greenhouse gas emissions. Although supplementary cementitious materials (SCMs) have been used massively, today in many countries there are some limitations in terms of the availability of traditional SCMs such as blast furnace slag and fly ash. Recently, limestone and calcined clay cements (LC3) have emerged as a viable alternative from a technical, economic and environmental point of view. These cements have become very attractive because low reactivity clay is practically found everywhere. In accordance with the above, this paper reports the results of a research aimed at understanding the key factors that controls the durability of LC3 concretes. Five LC3 blended mixes were formulated (SO3 content adjustment) and evaluated against carbonation and chloride ingress. Carbonation was measured in accelerated (3% CO2) and natural conditions simultaneously monitoring the reinforcement corrosion by linear polarization. Chloride ingress was assessed obtaining some transport properties such as the chloride migration coefficient from non-steady-state migration experiments and the chloride penetration from self-diffusion tests. Results showed that LC3 concretes have a high resistance against chloride penetration, increasing it notably with respect to the reference samples. Regarding corrosion resistance due to accelerated carbonation, LC3 concretes showed a lower performance which triggers an alert to evaluate its durability using also the carbonation exposure conditions and not only the chloride related properties.

Juan Lizarazo-Marriaga, Luis Felipe Salazar-Mayorga, Luis Eduardo Peña-Cruz
Effect of Chloride Concentration on the Freeze-Thaw Resistance of Concrete

Performance test methods intend to provide a fast, accurate and precise determination of a particular building material property and thus determine the associated material performance. In concrete, various performance tests are used to classify existing or to approve new materials, to compare concrete compositions or to determine causes of damage in existing structures. The challenge of such test methods is to accelerate natural (very slow) mechanisms to determine the material performance precisely within a short time. However, the attack on the material must not be unrealistically intensive, but must represent reality, just in fast motion. The performance tests used to demonstrate the freeze-thaw resistance of concrete employ a 3% NaCl solution, with literature data ranging from 1% to 10% showing that low concentrations can result in higher surface scaling. In this paper, mortar and concrete specimens are tested at 0, 1, 3, 6, and 9% NaCl solution following the CDF procedure (DIN CEN/TS 12390-9:2017-05). The results are discussed against the background of the existing literature and show that the damage is critically dependent on the pore system and thus also on the effect of the micro-ice lens pump. With increasing freeze-thaw exposition, the pessimum in the external damage shifts towards a de-icing salt concentration of 6%. Furthermore, a novel test methodology based on 3D-laserscanning is presented to determine scaling accurately by eliminating side effects that are typically present in current standards.

Alexander Haynack, Alexander Schneider, Jithender J. Timothy, Thomas Kränkel, Christoph Gehlen, Charlotte Thiel
Restoration of Degraded Calcium-Silicate-Hydrate in Calcium-Leached Cement Paste

Calcium leaching, a degradation process of cementitious materials, is a major concern in nuclear waste disposal facilities. Leached materials experience a drop in pH, dissolution of portlandite and degradation of other hydrated phases leading to a coarse microstructure, and thereby higher transport properties. Despite the fact that the mechanism and consequences of calcium leaching have been widely studied in the literature, little to no study has been done to evaluate the potential of reversing this process.The goal of this research is to investigate a structural repair process termed “recalcification”, which has a potential to reverse part of the calcium leaching, restoring the phase composition and structure of the deteriorated cementitious materials. CEM I cement paste with water/cement ratio of 0.5 was casted and cured for 48 days in sealed plastic tubes. Smaller specimens of size D × H = 10 × 7 mm were then leached in NH4NO3 6M for 24 h before being immersed in a bath of saturated Ca(OH)2 for recalcification. After 6 days, samples were freeze-dried and characterized with phenolphthalein spraying, FTIR, MIP and SEM-EDX.The results show that after recalcification, the Ca/Si ratio of the leached zone increases as the silicate chain length of C-S-H decreases. In the pores formed by leaching, a formation of web-like network of C-S-H is observed. As a result, the pore size distributions of recalcified samples shift from larger to smaller sizes, demonstrating the pore-filling effect during recalcification.

Thinh Nguyen, Quoc Tri Phung, Norbert Maes, Geert De Schutter, Özlem Cizer
Reaching Beyond Internal Curing: The Effects of Superabsorbent Polymers on the Durability of Reinforced Concrete Structures

With the current demands for more sustainable and durable structures, the search for smarter and innovative building materials plays a crucial role in the further development of the construction industry. The discovery of the synergetic effect between superabsorbent polymers (SAPs) and cementitious materials gave space to uncountable new possibilities. SAPs have since then been proven to effectively mitigate autogenous shrinkage, increase resistance to freeze-thaw damage, promote immediate sealing of cracks, enhance self-healing, etc. In this paper, the use of SAPs as internal curing agents in large-scale reinforced concrete walls is described with focus on the effects of internal curing on the crack formation and consequent corrosion initiation. Two reinforced concrete walls (with and without SAPs) were produced and monitored after casting. Multireference electrodes were used for monitoring the corrosion potential while the shrinkage strain was monitored by means of optical fiber sensors. Cracks were observed in the reference wall already five days after casting, while the SAP-wall remained crack-free after 24 months. The reference wall showed an indication of possible corrosion initiation near two of the crack locations six months after casting. In contrast, no corrosion potential was identified in the crack-free wall with SAPs.

José Roberto Tenório Filho, Nele De Belie, Didier Snoeck
The Effect of Temperature and Ageing on the Behaviour of Self-compacting Concrete Containing Supplementary Cementitious Materials

Self-compacting concrete (SCC) is increasingly replacing conventional vibrated concrete due to its high flowability and low energy demand during construction. The substantial proportion of paste found in SCC yields a different microstructure to conventional concrete, and thus, when subjected to different curing temperatures, it exhibits distinctive mechanical behaviour. However, the effect of curing temperature on SCC containing supplementary cementitious materials (SCMs) as partial cement replacements is yet to be thoroughly investigated. This paper aims to assess the behaviour of SCC with various SCMs cured at different temperatures to estimate the robustness and applicability of these mixes in concrete structures. For this study, certain percentage volume fractions of the cement in the SCC mixes were replaced by silica fume (SF), fly ash (FA), or ground granulated blast-furnace slag (GGBS). Tests were conducted on the fresh concrete to verify that the prepared mixes complied with the criteria for self-compacting concrete. Thereafter, cubes were made from the SCC mixes and cured at different temperatures (10, 20, 35, and 50 ℃). Cubic compressive strength tests were conducted at 1, 3, 7, 14, 28, 56 and 90 days. The results demonstrated that the strength gain tends to be slower at low curing temperatures (<20 ℃). In contrast, high curing temperatures (>20 ℃) could accelerate the strength gain in concrete but could also cause retardation of the strength development at a later age. However, using SCMs can make SCC more resistant to the detrimental effects of high curing temperatures.

Ayman Almutlaqah, Abdullah Alshahrani, Riccardo Maddalena, Sivakumar Kulasegaram
Study on Performance of Self-healing and Water Leakage Channel-Blocking Admixture for Mortar and Concrete

In recent years, there has been growing demand for sustainable concrete structures. One line of research is the addition self-healing properties to concrete. In this study, a natural pozzolan material known as “Bestone”, the product of a mine in Japan, is used as an admixture that blocks water leakage channels formed by cracking in concrete structures. It has previously been shown that when concrete including Bestone in the mix is applied to an underground structure, water leakage through microcracks decreases over several months until it stops entirely. In this study, in order to evaluate this water shutoff performance of Bestone mortars and concretes, a crack about 0.2 mm wide is artificially introduced into concrete specimens and changes in water leakage through the crack are measured. From the results, the water shutoff performance of Bestone is demonstrated. In order to investigate the mechanism of this behavior, SEM observations and X-ray diffraction analysis are carried out hydrates formed in the crack, clarifying that the pozzolan reaction occurs in the crack and that this leads to water shutoff. The effects of adding Bestone on the fresh properties and compressive strength of concrete are also evaluated.

Karen Ito, Hiromi Fujiwara, Masanori Maruoka, Kenji Kuwamoto
Exposure of Portland-Limestone Cement – Metakaolin Paste to Cold Chloride-Sulfate Environment: NMR Spectroscopy Assessment of Structural Changes in Hydrated Phases and Relation to Chloride Ingress

The effect of sulfates on chloride ingress and microstructure in Portland-limestone cement – metakaolin paste was studied. Crystalline and amorphous phases were investigated with X-ray powder diffraction and solid-state nuclear magnetic resonance spectroscopy. Free chlorides were determined with ion chromatography. The influence of metakaolin on the microstructure and chloride binding was highlighted by comparing the material with pure Portland-limestone cement paste. The results showed that the high Al content in metakaolin increased the chloride binding ability of the binder and Al incorporation in the C‒S‒H phase. Close to the surface, metakaolin admixture contributed in greater polymerization of the silicate chains of C‒S‒H, while larger amounts of unreacted clinker were observed, compared to deeper parts. At higher depths, chlorides bound in the form of Friedel’s salt and free chlorides, were considerably reduced, attributed to refinement of the matrix. The presence of sulfates in the exposure solution affected chloride binding by inhibiting the formation of Friedel’s salt and increasing free chlorides in the pore solution. Moreover, sulfates decreased the polymerization of the silicate chains in the C‒S‒H of the Portland-limestone cement – metakaolin paste and reduced the hydration of clinker in pure Portland-limestone cement paste.

Konstantinos Sotiriadis, Anton Mazur, Peter Tolstoy, Radek Ševčík
A Literature Review of Shrinkage in Repair Materials with Fine Materials

Concrete structures are susceptible to physical and chemical degradation over time, making repairs a complex process that requires careful consideration of the repair material's compatibility with the substrate. The durability of the repair/substrate system largely depends on dimensional compatibility, and the shrinkage of the repair material can cause premature cracking, reduce load-bearing capacity, and allow for the penetration of corrosive substances. The inclusion of fine materials, such as powders and fillers, with varying origins and mineralogical compositions, can influence the microstructure of cement-based materials and impact shrinkage mechanisms. This review focuses on the effects of calcitic limestone, dolomitic limestone, and magnesium oxide (MgO) on shrinkage and mechanical properties in mortars and the mechanisms involved in the hydration process. This literature review is the first stage of a research project titled “Special Cement Materials for Repairs of Dam Structures (REPAIRMAT II)”, which is a collaborative effort between the Itaipu Hydroelectric Plant (IB), the Federal University of Latin American Integration (UNILA), and the Itaipu Technological Park (PTI) in Brazil. The project aims to investigate the potential benefits of incorporating fine materials in repair mortars for concrete structures, with a goal of improving the durability and longevity of concrete dams.

Luan Reginato, Étore Funchal de Faria, Luis Antonio Sucapuca Aracayo, Ana Carolina Parapinski Santos
Effect of Elevated Temperature on the Strength of Date Palm Fiber Reinforced Concrete Containing Silica Fume

Date palm fiber (DPF) is an agricultural, organic, and fibrous material. Therefore, when used as fiber in concrete that is subjected to higher temperature, it can easily degrade and cause reduction in strength. Hence, there is a need to investigate the effect of elevated temperature on the weight loss and strengths of the DPF reinforced concrete. In this study, the fiber reinforced concrete was produced by adding different proportions of DPF at 0%, 1%, 2% and 3% by weight of cementitious materials. Cement was partially replaced with silica fume in proportions of 0%, 5%, 10% and 15% by volume. The concrete was subjected to elevated temperatures of 200 ℃, 400 ℃, 600 ℃ and 800 ℃ for 2 h. The weight loss and compressive strength after subjecting to high temperatures were investigated. The results showed that the weight loss escalated, and the compressive strength of the concrete decreased with the increment in the elevated temperature and DPF content. At a temperature above 600 ℃, the increment in weight loss and reduction in strength became more severe. The addition of silica fume as partial substitute to cement led to reduction in the weight loss and decrease in compressive strength of the DPF reinforced concrete when heated to a temperature up to 400 ℃., However, at higher temperature above 400 ℃, the addition of silica fume to the DPF reinforced concrete led to further escalation in weight loss and reduction in strength. The physical observation revealed that when the concrete was subjected to higher temperature, its surface color changed to light grey, some cracks were observed on the surface. The DPF reinforced concrete was able to withstand up to 400 ℃ temperature without spalling, after which severe spalling was observed with the DPF degraded.

Musa Adamu, Yasser E. Ibrahim, Mohammad Louay Marouf
New Repair Approach Using Ultra-high Performance Fibre Reinforced Concrete for Structures Affected by Alkali-Aggregate Reaction

Several concrete structures are affected by alkali-aggregate reaction (AAR). In presence of water, AAR causes swelling of the structure that induces crack in the concrete, alters its mechanical and durability properties and brings functionality problems. This project proposes a novel repair approach that consists in casting a thin ultra-high performance fibre reinforced concrete (UHPC) shell around the affected structure. This repair takes advantage of the exceptional mechanical and durability properties of UHPC to limit water ingress into the affected structure and to contain swelling that could occur. A new ring testing device was developed to simulate the solicitations occurring in such a repair, i.e. shrinkage restriction of the repair by the substrate at early age and then expansion caused by AAR. These tests were performed on a reference high-performance concrete (HPC) as well as on a UHPC with 3% fibre volume, with or without joint, and with or without rebar in the repair. The results showed that the unreinforced HPC repair cracked under restrained shrinkage condition, whereas the unreinforced UHPC repair remained uncrack with 0.2% of tensile strain still available to contain expansion due to AAR before localization of a macrocrack. When adding a rebar ratio of 1.2% in the UHPC repair, the tensile strain available for expansion was even higher with a synergic effect of fibres and rebar.

Clélia Desmettre, Jean-Philippe Charron, Sarra Abid
Toward Sustainable Strengthening Systems for RC Structures

Strengthening of reinforced concrete (RC) structures has been always a great engineering deal. Nowadays, with the global awareness of the environmental impacts of construction industry, and specially the considerable share of this sector in CO2 emission and global warming, it is of a great importance to increase the service life of existing structures. The near surface mounted (NSM) technique with carbon fiber reinforce polymer (CFRP) composites is proved to be very effective for the strengthening of RC structures. However, the toxicity and poor fire resistance of epoxy resins used to bond CFRP to concrete substrate, have promoted research for finding alternative adhesives. This study is dedicated to propose an innovative approach for the application of cement-based adhesives with sand-coated CFRP strips, using the NSM strengthening technique. The bonding performance of the proposed system is evaluated through direct pull-out tests in ambient and thermo-mechanical conditions. The environmental aspects of using cementitious materials as an adhesive for NSM CFRP systems are also discussed as a preliminary step in the development of sustainable and eco-friendly strengthening systems to increase the service life of the RC structures.

Reza Mohammadi-Firouz, Joaquim Barros

Carbonation of Concrete with Supplementary Cementitious Materials (TC 281-CCC)

Carbonation Performance of Hybrid Ternary Binders Containing Low-Calcium Fly Ash and Sodium Sulfate

Hybrid binders emerge as a solution to further decrease the clinker factor in cementitious systems without unfavorable slow strength development.The Portland cement reduction not only produces greener systems, but also makes them more sensitive to carbonation, especially due to the very limited amount of portlandite available. Therefore, the pore structure is expected to be affected differently by carbonation. This paper aims to clarify the behaviour of different ternary binders containing 50% FA and 8% Na2SO4 as activator. SCMs/total binder ratio was 0.7, w/b was 0.45. Results of accelerated carbonation (1% CO2) on mortars are presented. Mixes were cured for 28 days and subjected to a preconditioning process of 28 more days. The carbonation rate of different mixes suggests a synergy effect occurring among FA, GGBFS, and sodium sulfate. A reference mix containing quartz instead of fly ash was also studied in order to isolate the contribution of the former to the carbonation resistance. GGBFS and Na2SO4 addition refined the pore structure. The microstructural damage due to carbonation process was also addressed by MIP analysis and revealed a more dense matrix than the one for ternary mixes without sodium sulfate after carbonation.

J. M. Etcheverry, P. Van den Heede, Y. A. Villagran-Zaccardi, N. De Belie
Carbonation Rate of Alkali-Activated Concretes: Effects of Compositional Parameters and Carbonation Conditions

The current ability to predict the carbonation resistance of alkali-activated materials (AAMs) is incomplete, partly because of widely varying AAM chemistries and variable testing conditions. To identify general correlations between mix design parameters and the carbonation rate of AAMs, RILEM TC 281-CCC Working Group 6 compiled and analysed carbonation data for alkali-activated concretes and mortars from the literature. For comparison purposes, data for blended Portland cement-based concretes with a high percentage of SCMs (≥66% of the binder) were also included in the database. The results show that the water/CaO ratio is not a reliable indicator of the carbonation rate of AAMs. A better indicator of the carbonation rate of AAMs under conditions approximating natural carbonation is their water/(CaO + MgOeq + Na2Oeq + K2Oeq) ratio, where the index ‘eq’ indicates an equivalent amount based on molar masses. This finding can be explained by the CO2 binding capacity of alkaline-earth and alkali metal ions; the obtained correlation also indicates an influence of the space-filling capability of the binding phases of AAMs, as for conventional cements. However, this ratio can serve only as an approximate indicator of carbonation resistance, as other parameters also affect the carbonation resistance of alkali-activated concretes. In addition, the analysis of the dataset revealed peculiarities of accelerated tests using elevated CO2 concentrations for low-Ca AAMs, indicating that even at the relatively modest concentration of 1% CO2, accelerated testing may lead to inaccurate predictions of their carbonation resistance under natural exposure conditions.

Gregor J. G. Gluth, Xinyuan Ke, Anya Vollpracht, Lia Weiler, Susan A. Bernal, Martin Cyr, Katja Dombrowski-Daube, Dan Geddes, Cyrill Grengg, Cassandre Le Galliard, Marija Nedeljkovic, John L. Provis, Luca Valentini, Brant Walkley
Insight from Modeling Service Life of Low-Clinker Cements at Moderate Relative Humidity Under Carbonation Attack

Either for desired properties or sustainability needs, cement industry has been incorporating SCMs in cement, bringing down the clinker factor for the last few decades. Incorporation of SCMs results in a changed microstructure and pore solution composition. These are the main factors other than environmental conditions that influence both the initiation and propagation phases of reinforced concrete structures’ service life under carbonation conditions. Modeling the physical processes involved during service life can help to give a better insight into the relative importance of the factors involved. In this study, a numerical model for combined initiation and propagation phases was developed and employed to understand the significance of factors such as diffusion coefficient, buffer capacity, resistivity, and the fraction of corrosion products diffusing in concrete on the prediction of service life. After performing simulations and analysis, the diffusion coefficient to buffer capacity ratio had been realized to be a better parameter for comparing carbonation resistance among various blended cements. Additionally, it has been observed that low-clinker cements give comparable or lower life in the propagation phase, which is due to altered porosity resulting in reduced resistivity upon carbonation. It had been concluded that to compare low clinker cement it is better to compare them based on their carbonated transport properties and initial buffer capacity as properties of non-carbonated concrete may be misleading.

Lupesh Dudi, Shashank Bishnoi
Influence of Blended Cements on the Service Life of Reinforced Concrete Structures against Carbonation Induced Corrosion

Corrosion due to carbonation is a major factor in reducing the service life of reinforced concrete structures exposed to the environment. The problem is more pronounced in concretes that are made with composite cements. In this case, both the total percentage of pozzolanic materials and their type play an important role. In this work, the effect of three different cements on the carbonation of concrete is examined. Concretes with different w/c ratios were prepared using one ordinary Portland cement (CEM I 42.5N) and two blended cements - CEM II (A-M) 42.5N and CEM II (B-M) 42.5N. The depth of carbonation after curing in a carbonation chamber with a carbon dioxide concentration of 2% was measured. Service life of reinforced concrete structures was calculated using the model referred to in FIB MC 2010 for structures exposed to different environmental conditions. The results show that blended cements increase the vulnerability of concretes against carbonation and reduce the service life of reinforced concrete structures exposed to environmental conditions typical of those of the Mediterranean countries. In order to overcome this problem, it is suggested to increase the initial wet curing period of the casted concrete.

Kosmas K. Sideris, Panagiota Manita
Corrosion Kinetics of Steel in Carbonated Pore Solutions Containing Chlorides and Sulphates

The carbonation of cementitious materials is often attributed to be one of the major causes of corrosion in reinforced concrete, possibly leading to premature deterioration. When assessing the effect of carbonation on corrosion, most studies are limited to measuring the carbonation rates of different concretes. From these, replacing clinker with supplementary cementitious materials – one of the main strategies to reduce CO2 emissions – was found to increase the rate of carbonation. However, a more urgent question concerns the actual corrosion kinetics of steel in carbonated systems, accounting for factors such as the pore solution composition, microstructure, and moisture of the cementitious matrices. To address this topic, this study focuses on the effect of carbonated pore solutions on the kinetics of steel corrosion. Steel samples were immersed in artificial pore solutions representative of carbonated binders, at pH 8.1, under aerated conditions. Furthermore, the role of aggressive species, such as chlorides and sulphates, was examined to assess their potential significance in carbonated media. The steel-solution systems were monitored through open circuit potential (OCP) and polarization resistance (Rp). Understanding the isolated impact of the pore solution on steel corrosion will support further studies combined with the microstructure and moisture states of carbonated reinforced concretes, crucial to safely assure the durability of environmentally friendly structures.

Cristhiana Albert, Shishir Mundra, O. Burkan Isgor, Ueli Angst
Carbonation Resistance of Recycled Aggregate Concrete Using Different Cement Types

This paper describes the influence of the cement type and the use of 50% coarse RCA on the carbonation resistance of concrete. Twelve concrete mixtures were produced using four types of cement (CEM I, CEM IIAL, CEM IIAS and CEM IV of 42.5 MPa) and three different types of coarse aggregates (natural, RCA and carbonated-RCA [C-RCA]). All the concretes used 300 kg of cement and an effective water/cement (w/c) ratio of 0.49. The compressive strength at 28 and 56 days and the carbonation rate (at the accelerated and natural carbonation test) were determined and analysed. In both carbonation processes, it was concluded that while the concretes produced with CEM IV achieved the highest carbonation rate, the IIAS concretes achieved the lowest, regardless of the types of aggregates employed. On the other hand, the concretes produced with RCA and C-RCA achieved similar carbonation rate properties. Moreover, the natural carbonation coefficient, knat, determined experimentally, was 1.6–1.8 times higher than the carbonation rate estimated by the accelerated test. According to knat and following the structural code, all the concretes produced with CEM IV and the concrete produced with IIAL cement and C-RCA aggregates would not be allowed to be used in reinforced concrete exposure to a XC4 environment.

Miren Etxeberria
On the Carbonation Dilemma and How to Escape from It

There is a dilemma between designing cementitious binders with low greenhouse gas (GHG) emissions and at the same time attempting to satisfy carbonation test requirements. In fact, various studies have shown that with increasing clinker replacement, the carbonation rate increases. The established paradigm to ensure durability, particularly to avoid reinforcement corrosion related damage, is based on avoiding carbonation of the concrete, as carbonation is conceptually equated with corrosion. This view presents a major goal conflict, and has important consequences for the ambition to reduce GHG emissions from the cement and concrete industry. The requirement to avoid carbonation penalizes binders with high clinker replacements in comparison with Portland cement.To overcome this barrier and to unleash the full potential of low carbon binders, there is thus an urgent need to escape from this “carbonation dilemma”. This conference contribution discusses how new insight with regard to the mechanism of corrosion of steel in concrete presents an opportunity to resolve the mentioned dilemma. There is increasing evidence that the moisture at the steel surface is the more important factor to ensure durability than whether or not the concrete carbonates. This way of looking at durability is underpinned by the findings of a working group within RILEM TC 281-CCC as well as recent scientific laboratory studies. A review of this literature is presented and a vision of a possible escape route from the “carbonation dilemma” is sketched.

Ueli M. Angst
Study on Properties of UFC Cured by Autoclaving

Ultra-high-strength fiber-reinforced concrete (UFC) achieves high strength and greater durability by the addition of metal fibers and certain admixtures at very low water-powder ratios. UFC has been utilized not only for large concrete structures but also for the repair and reinforcement of existing structures. In recent years, demand for precast UFC products has increased. However, the production of UFC components requires long periods of steam curing at high temperatures. In this study, with the aim of improving productivity by attaining ultra-high-strength earlier than with steam curing, autoclave curing at 180–190 ℃ and 10–11 atm pressure is experimentally applied to UFC. The optimum combination of powders and metal fibers is investigated through experiments. It was found that a compressive strength of 180 N/mm2 or more and a flexural strength of 30 N/mm2 or more can be achieved in a shorter time by autoclaving. In freeze-thaw tests, chloride ion penetration tests, and accelerated carbonation tests, sufficient durability was confirmed.

Junon Yoshikawa, Hiromi Fujiwara, Masanori Maruoka, Kotaro Yoshikawa, Katsuhiko Yamada
The Impact of Chloride Binding on the Resistance to Carbonation: From Single Cycle Degradation Towards the Complexity of Multi Cycle Degradation

It is general practice to predict the service life of a reinforced concrete structure based on a prevailing single degradation mechanism. However, in real life environments, different degradation mechanisms will interfere with the cement matrix and it is clear that their interaction disables a simplification of service life prediction based on a dominant single degradation. The two most common deleterious agents for reinforced concrete structures are CO2 and chlorides leading to possible carbonation or chloride induced corrosion. To assess the impact of combined degradation, first the single cycle impact of chloride binding on the carbonation rate was investigated for concrete with CEM I and CEM I partially replaced by ground granulated blast-furnace slag (GGBFS) (40wt% and 70wt%). Based on the outcomes, it is clear that chloride binding leads to a densification of the pore structure resulting in a binder dependent impact on the carbonation rate. To upscale the outcomes from single cycle experiments towards a multi cycle degradation system, the complexity of the problem increases significantly. This paper will report on the influence of wetting and drying, and also chloride binding on the carbonation rate of concrete with GGBFS (0wt%, 40wt% and 70wt%) exposed to cyclic carbonation at 1% CO2 for 13 days and 3% NaCl submersion for 1 day. The outcomes of the paper will lead to a better understanding of combined degradation and can serve as experimental benchmark data for the service life prediction models.

Hanne Vanoutrive, Peter Minne, Özlem Cizer, Elke Gruyaert
Influence of Curing Type and Duration on the Resistance to Accelerated Carbonation and Its Relation to Natural Indoor and Outdoor Sheltered Carbonation

The assessment of the resistance to carbonation of cement based materials is, because of practical considerations, mostly based on accelerated carbonation tests at elevated CO2 concentrations. However, experimental research already pointed out that results originating from accelerated carbonation tests are not completely representative for the natural carbonation resistance. This is caused by the altered reaction mechanisms due to the elevated CO2 concentrations resulting in deviating reaction products (e.g. CaCO3 polymorphs), an increased amount of water released during carbonation, etc. Moreover, the maturity of a cement paste matrix prior to exposure has a greater impact in case of accelerated carbonation compared to natural carbonation. Especially when adding supplementary cementitious materials (SCMs) to partially replace Portland clinker, the pozzolanic or latent-hydraulic behaviour might result in a less developed microstructure at early ages. As a consequence, extrapolated and/or converted results from accelerated carbonation tests on young mortar may misrepresent the performance under natural carbonation. This paper reports on the influence of curing type (sealed versus water) and duration (13, 28 and 90 days) on the carbonation rate of CEM I, CEM II/B-V and CEM III/B mortar exposed to 1 vol% CO2. Moreover, a comparison was made with carbonation rates based on natural carbonation of the same mixes both in an indoor and outdoor sheltered environment and sealed cured for 13 days prior to exposure. In general, the outcomes indicate that the reference water curing in combination with accelerated carbonation at 1 vol.% CO2 best represents the natural behaviour for the different cement types.

Hanne Vanoutrive, Peter Minne, Özlem Cizer, Elke Gruyaert
Comparing the Carbonation Performances of a Low-Clinker Blended Slag Cement with an Alkali-Activated Slag via Thermodynamic Modelling

Carbonation, reactions between cementitious materials and atmospheric carbon dioxide, is one of the most important mechanisms that determine the longevity of cementitious materials. Despite the recent advances in revealing the carbonation mechanism of cement and concrete materials, the understanding of carbonation mechanisms in low-carbon cementitious materials, particularly low-clinker blended cement (clinker replacement > 60%) and alkali-activated materials, is still limited. This study compares the carbonation performances of a low-clinker blended slag cement and an alkali-activated slag cement via thermodynamic modelling. Phase assemblages of two different types of cementitious materials under accelerated carbonation conditions were predicted by thermodynamic models using the latest CEMDATA18 database. Validation of the developed models were conducted by comparing the predicted results with the experimentally characterised mineralogy from the literature. After validation, the carbonation performances of high-GGBFS blended cement and alkali-activated slag cements are critically compared.

Xinyuan Ke
New Insights into the Carbonation Process of Mortars and Concretes

The carbonation of cementitious materials leads to measurable changes in the material’s physicochemical properties: formation of carbonates, dissolution or decalcification of Ca-containing hydrate phases, changes in porosity and decrease of pore solution pH. The presence of supplementary cementitious materials leads to changes in the mineralogical composition and porosity of the hardened material and thus to changes in the carbonation process compared to pure Portland cement mixtures. In this study, the carbonation of concrete and mortar mixtures with varied clinker content under accelerated conditions was investigated. The carbonation progress was visualized via phenolphthalein (PHPHT) and quantitively using optical pH imaging techniques. Thermogravimetry and XRD was used to measure the portlandite content at individual depths of the carbonated samples. The investigations showed that the actual pH value of the clearly carbonated regions (= PHPHT colourless) of different samples can vary between 9.2 and 10.5. Thereby, with decreasing clinker content, a decreasing pH in the “PHPHT colourless” area was observed after the same time of accelerated carbonation. Measurable portlandite concentrations in the samples exhibiting higher pH in these regions support the findings. The obtained results highlight the strong impact of physicochemical material properties on the carbonation process and the corresponding risk of corrosion. The study shows that the PHPHT-test can only partially answer questions related to carbonation processes whereas the new optical imaging method allows for a better understanding of the carbonation state of cementitious systems.

Marlene Sakoparnig, Isabel Galan, Bernhard Müller, Iris Zoegl, Joachim Juhart, Florian Mittermayr, Michael Autischer, Cyrill Grengg
Long-Term Natural Carbonation in Concretes with Fly Ash and Limestone Calcined Clay Systems

The use of supplementary cementitious materials (SCMs) in concrete is a sustainable solution. However, many practitioners and researchers perceive the lower resistance of SCM-based concretes against carbonation as a concern for large-scale implementation. It must be noted that most literature discusses the carbonation resistance of SCM-based concretes performed in accelerated carbonation. These accelerated carbonation results should be compared with natural carbonation results to predict the reliable performance of SCM-based concretes against carbonation in natural exposure conditions. Therefore, studies on the long-term natural carbonation of concrete with various SCMs were conducted in Chennai, India (hot-humid, tropical climate). This study has 21 concrete mixes with various SCMs (ordinary Portland cement, fly ash, and limestone calcined clay systems), water-to-binder ratios, and compressive strength grades. The specimens were exposed to natural atmospheric conditions for about 10 years in sheltered and open exposure. The sheltered specimens showed higher carbonation depths than the open-exposure specimens. It was observed that the type and replacement levels of SCMs, water-to-binder ratio, paste content, etc., could influence the carbonation resistance. The long-term natural carbonation study concluded that concretes with SCMs offer higher resistance to carbonation at a later stage of carbonation—hence, necessitating the decision-making based on models made using long-term natural carbonation.

Sundar Rathnarajan, Umesh Hule, Radhakrishna G. Pillai, Ravindra Gettu
Influence of Fly Ash as Cement Substitution on Accelerated and Natural Carbonation of Concrete

The use of fly ash (FA) for the production of new concrete seems to be a promising solution for “greening” of construction industry. However, replacement of cement with supplementary cementitious materials such as fly ash influences concrete performance especially in terms of durability. One of major durability problems worldwide is carbonation-induced corrosion, given that a large number of infrastructural objects are exposed to a CO2-rich environment. The objective of this research was to analyse the influence of cement substitution level on accelerated and natural carbonation of concrete. Experimental program considered testing of 10 concrete mixtures selected in two groups – with water to binder ratio of 0,5 (400 kg/m3 of binders) and 0,6 (300 kg/m3 of binders), while in each group the cement substitution ratio was varied from 0% to 50%. Carbonation depth was measured after 14, 21 and 28 days of exposure to 2% CO2 in carbonation chamber, while the twin samples were exposed to natural carbonation. It was shown that accelerated carbonation depths were similar in both groups for mixtures up to 30% of FA, but they were doubled and tripled for larger replacement levels. Using the previously modified fib carbonation model for service life design, the prediction of natural carbonation was made. A reliability of proposed modification was assessed by comparison between predicted and measured values of natural carbonation after 19 and 34 months of exposure.

Vedran Carević, Aleksandar Radević, Ivan Ignjatović
Carbonation of Concretes with Different Binder Chemistry – A Comparative Analysis

The need to reduce clinker production has focused research on the use of various alternative binders in place of ordinary Portland cement (OPC). Although there is a general knowledge of the performance of these materials, there is still a great need to understand and predict their long-term durability for their potential application. One of the critical durability parameters is carbonation resistance. The reaction between CO2 in the atmosphere and calcium-bearing phases in the binder changes the binder chemistry and leads to corrosion of the embedded steel which reduces the durability of the concrete. The mechanism and kinetics of carbonation in different binder systems depend on the type of the hydration products formed. This research presents the comparative analysis of the phenomenology of the carbonation process of OPC concrete and four alternative binder systems: calcium aluminate cement concrete, high volume fly ash concrete, LC3 and alkali-activated slag concrete. Carbonation resistance was tested by measuring the carbonation front after 7 and 28 days of accelerated carbonation with 3% CO2 and 57% relative humidity at 20 ℃. The microstructural changes induced by carbonation were analyzed by mercury intrusion porosimetry and thermogravimetric analysis.

Matea Flegar, Alma-Dina Bašić, Olivera Bukvić, Marijana Serdar
Influence of Humidity and Loading on Carbonation and 4-Point Bending Strength of Slag Cement Mortar

The production of Portland cement generates a significant amount of greenhouse gas emissions. In the current context of sustainable development, it is essential to reduce this effect. That is the reason why a great deal of research is being carried out to develop new, more ecological materials. These materials must have the least possible impact on the environment throughout their life cycle. They must have good mechanical properties and durability, particularly with regard to carbonation. Indeed, they are exposed to the ambient air and consequently to the carbon dioxide present in it. Moreover, these various structures are often subjected to mechanical stresses. The main objective of this research, within the framework of the WG4 of the RILEM TC 281-CCC, is to study the effects of the carbonation on the mechanical behavior and conversely the effects of the mechanical solicitation during the process of accelerated or natural carbonation. These structures are based on cement with a high content of blast furnace slag. The impact of natural and accelerated carbonation at 2% and 20%CO2 on the different properties of mortars was studied. As the surrounding humidity is an important factor of carbonation, its influence is also studied. The tests were carried out on 7 × 2 × 28 cm3 specimens having undergone a pre-conditioning during 28 days. Different formulations and loading rates were studied. The results showed that the mechanical loading imposed during carbonation tests has an impact on the deflection and on the carbonated thickness. In particular, an increase in carbonation depth is observed under tensile stress and a slight decrease in carbonation depth is measured under compressive stress.

Elodie Piolet, Siham Kamali-Bernard
Effect of the Carbonate Source on the Carbonation Performance of Blended Binders Containing Calcined Clays

There is a burgeoning interest in determining the feasibility of using different clay types as potential supplementary cementitious materials (SCMs), for the production of more sustainable concretes. Given the connection between sustainability and longevity of construction materials, attention needs to be paid to the potential threats new SCM-containing cements might undergo. This will enable the design of materials accounting for environmental savings during production and improved resilience and longevity.This research is part of the collaborative USA-UK project ‘RENACEM’ aiming to understand the response to CO2 exposure of sustainable cements containing calcined clays as SCMs. The present study reports the outcomes of the carbonation performance studied in selected Portland blended specimens exposed to accelerated or natural carbonation evaluating the influence of limestone or dolomite addition. Compressive strength development, carbonation depth and microstructural changes induced by CO2 exposure were determined. Clinker content governs the carbonation rate of both binary and ternary formulations in accelerated carbonation. Natural carbonation samples exhibited similar carbonation depths independently of the carbonate type used, conversely to those exposed to accelerated carbonation testing.

Yuvaraj Dhandapani, Srajan Bhadauria, Sreejith Krishnan, Maria C. G. Juenger, Susan A. Bernal

Chloride Transport in Alkali-Activated Materials (TC 283-CAM)

Microstructure and Performance of Three Silicate Binders in the Range CSH-CASH-NAS

Although silicate binders from side streams are very attractive to use in terms of CO2-reduction and primary material reduction, their performance may deviate from that of already accepted cements. Structural design codes then may not be valid anymore. The performance of these new binders thus have to be determined. In this paper, the microstructures and the relation to performance is investigated from three binder systems, based on the currently most common precursors. Mortars were designed for similar paste volumes. Microstructural analysis showed furthermore also very similar total porosity and pore size distribution but three different reaction products: CSH with some Na and Al for the activated slag, CASH with a high amount of sodium for the activated slag/fly ash blend and NAS for activated metakaolin. The three types of binders have a similar slow compressive strength development, although they have very different 28-days strengths. The 28-day strength is only 2/3 of the predicted ultimate strength. In contrast, the bending strength and Young’s modulus developed either faster (CSH) or slower (NAS) than the compressive strength, leading to an over- or underestimation of these properties predicted on the basis of the 28-day strength in the structural design codes. Application of these binders in concrete within the framework of the current model codes thus is not allowed. The methodology of binder design as well as performance validation by combining microscopy with macroscopic properties was found to be quite efficient. As such, it may contribute towards establishing new model code for new binders in the future.

Jeanette Visser, Juan Garzon-Amortegui, Timo Nijland, Sacha Hermanns
Testing Geopolymer Concrete Performance in Chloride Environment

The major barriers to geopolymer concrete widespread adoption by the construction industry are concerns about durability and exclusion from current standards. Chemical reactions characterizing alkali-activated binder systems differ drastically from conventional hydration process of Portland cement. Thus, the mechanisms by which concrete achieves potential durability are different between the two types of binders. As a result, testing methods and performance-based requirements for geopolymer must be developed to be incorporated in a performance base standard.The standard ASTM C1202 RCPT fails to measure the charges passed through most of geopolymer concretes. A modified version of RCPT using 10V (as opposed to 60V specified by standard ASTM C1202) is considered, allowing to successfully complete the tests for all geopolymer concretes. Various precursors are investigated including fly ash, GGBFS, calcined clay and ferronickel slag. Different activators are also considered. A good correlation is observed between modified ASTM C1202 and Standard ASTM C1556 bulk diffusion test results. Performance-based specifications are proposed.

Quang Dieu Nguyen, Samuel De Carvalho Gomes, Mohammed Fouad Alnahhal, Wengui Li, Taehwan Kim, Arnaud Castel
Correlation Between Chloride Ions’ Migration and Diffusion Coefficients of Alkali-Activated Concrete

Alkali-Activated Materials (AAM) are considered an alternative to cementitious binders. Due to the reduction of Portland cement content and using industrial wastes to produce it, AAMs gained the researcher's interest in the last decades. Current researches show that mechanical properties and ability to ensure proper conditions for reinforcing steel of AAMs are at least as good as for Ordinary Portland Cement (OPC) concrete. However, environmental aggression affects the durability of AAMs in a different way than OPC. For this reason, there is a necessity to develop the available testing methods dedicated to cement concrete and adjust them to a new type of binder. One of the aggressive environments is a marine zone, where the chloride ions affect the properties of structures. In this paper, the comparison of results obtained from chloride penetration tests conducted on three Alkali-Activated Concrete (AAC) mixtures will be presented. The binders’ precursors are the blends of Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS) in slag proportions: 5%, 20%, and 35% expressed by the mass of FA. Materials are denominated AAC5, AAC20, and AAC35, respectively. Chloride penetration tests were conducted using the modified NT BUILD 492 rapid migration test, and reference ASTM C1556 chloride diffusion test. The correlation of results shows the necessity of applying the adjustments to the rapid migration test for AACs. In both tests, the positive influence of increasing slag content was determined. The possible reasons for the observed tendencies are presented and explained.

Patrycja Duzy, Izabela Hager, Marta Choińska, Ouali Amiri
International RILEM Conference on Synergising Expertise towards Sustainability and Robustness of Cement-based Materials and Concrete Structures
herausgegeben von
Agnieszka Jędrzejewska
Fragkoulis Kanavaris
Miguel Azenha
Farid Benboudjema
Dirk Schlicke
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