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2023 | Buch

Proceedings of the 75th RILEM Annual Week 2021

Advances in Sustainable Construction Materials and Structures

herausgegeben von: J. Ivan Escalante-Garcia, Pedro Castro Borges, Alejandro Duran-Herrera

Verlag: Springer International Publishing

Buchreihe : RILEM Bookseries


Über dieses Buch

This volume gathers the latest advances, innovations and applications in the field of sustainable construction materials and structures, as presented by leading international researchers and engineers at the 75th RILEM Annual Week (75RW 2021), held in Merida, Mexico on August 29 – September 3, 2021. It covers topics such as supplementary cementitious materials, durability and Life Cycle assessment in urban and marine conditions, additive manufacturing of concrete in construction, structural performance and design, non-Portland cements and Alkali activated cementitious materials and eco-concrete, cultural heritage, non-destructive testing techniques, bituminous materials, and construction materials (polymers, timber, bamboo, recycling and masonry). The contributions, which were selected through a rigorous international peer-review process, share exciting ideas that will spur novel research directions and foster new multidisciplinary collaborations.



Supplementary Cementitious Materials

Freeze Thaw Resistance of Non-ferrous Slag Concrete

The objective of this work is to study the freeze thaw resistance of supplementary cementitious materials (SCM) based concrete made from non-ferrous slag (NFS) benchmarked with CEM I 52.5 N and CEM III 42.5 B concrete. NFS is synthesized during the production of Cu metal from Cu scraps. The freeze thaw resistance of NFS concrete containing 70% CEM I 52.5 R and 30% NFS (w/b = 0.45) as binder, as well as of CEM I 52.5 N and CEM III 42.5 B concrete was tested following CEN TR 15177 (2006). The analysis was based on a calculation of the relative dynamic elastic modulus determined by ultrasonic measurements and a determination of the water absorption by mass in function of the number of freeze thaw cycles. Furthermore the relative tensile strength loss after 56 cycles was considered and a microstructural analysis was performed. All concrete mixes showed a relative tensile strength after 56 freeze thaw cycles lower than 100% of the initial value, whereas the CEM III 42.5 B concrete showed the highest strength loss of around 15% followed by 11% for NFS concrete. NFS concrete also showed highest water uptake of around 4% whereas CEM I 52.5 N and CEM III 42.5 B concrete showed values of 1.2% and 2.2% respectively.

Pithchai Pandian Sivakumar, Nele De Belie, Stijn Matthys, Elke Gruyaert
Investigating Supplementary Cementing Materials for Alkalis and Pore Fluid Properties

Dwindling supplies of quality fly ash in many parts of the world necessitates an expeditious search for supplementary cementing materials (SCMs) to conform to the growing demand for sustainable materials in partially substituting for Portland cement in concrete. In recent years finely-ground waste glass, landfilled/ponded coal ashes and natural pozzolans have (re)drawn the attention of researchers and the industry to become potential SCMs. In this study a wide range of such SCMs were characterized for water-soluble and available alkalis using ASTM C114 and ASTM C311. Inductively coupled plasma emission spectroscopy (ICP-ES) was employed to determine the amounts of alkalis. Cementitious pastes containing Portland cement and SCM were prepared at a 0.5 water-to-cementing materials ratio and stored in airtight containers at 23 ℃. The pore solution of these pastes at 28 and 91 days was analyzed for hydroxyl ion (OH–) concentration, and strengths of alkali ions (Na+ and K+) using ICP-ES. The results indicate that all alkali oxides of SCMs are generally neither water-soluble nor available. Except for the high-alkali ground glass and high-calcium fly ash, the use of all other reactive SCMs considerably decrease the presence of the hydroxyl and alkali ions in the pore solution in the long-term.

Mahipal Kasaniya, Michael D. A. Thomas
Calcination and Reactivity of Marlstones: A Comparison Between Palygorskite and Smectite Bearing Marlstones

In the race to reduce greenhouse gas emissions, the cement industry appears to be a bad pupil and is responsible for non-negligible pollution, particularly due to clinkerization. Calcined clays are among the most promising Supplementary Cementitious Materials (SCMs) and allow a significant reduction in the environmental footprint of cement manufacturing. Many secondary resources, which are considered as waste by the mining industry, contain clay phases, and are therefore potentially recoverable as SCMs once calcined. This study focuses on the calcination and reactivity of two marlstones (MS1 and MS2) from a phosphate mine. The evolution of the phases as well as the physico-chemical modifications induced by calcination and hydration were characterised by X-ray diffraction (XRD) and Solide State Nuclear Magnetic Resonance (MAS NMR). The two materials are relatively similar and mainly composed of dolomite, associated with clay phases (smectite and biotite), quartz and other minority phases. The main difference between the two materials is the occurrence of palygorskite – a particular TOT clay mineral - in the MS1 sample. The calcination of these two materials resulted in a significant dehydroxylation of the clay phases, a dissociation of the dolomite into lime and periclase and the formation of dicalcium silicate. The self-reactivity of the samples in the presence of water was then tested in order to determine the evolution of the reactive phases (lime, periclase, dicalcium silicate) and to test the pozzolanic reactivity of the calcined clay phases. The results show a strong reactivity of the MS1 sample (mainly pozzolanic) while MS2 exhibits a lower reactivity. The presence of palygorskite in the MS1 material improves its reactivity once calcined, it thus seems that this unconventional clay has a promising pozzolanic reactivity, which opens new ways of valorization for this type of secondary resources.

Victor Poussardin, Michael Paris, William Wilson, Arezki Tagnit-Hamou, Dimitri Deneele
Effect of the Formulation on the Hydric and Mechanical Properties of Flax Concrete: Comparison with Hemp Concrete

The incorporation of waste plant particles in a cementitious matrix has led to obtain high-performance materials with good economic and ecological benefits. In this paper, a characterization of the main hydric and mechanical properties of a new material composed by flax shives was performed. The aim is to study the impact of the flax shives content on its hydric and mechanical behavior. Moreover, a comparison between the behavior of this material and those of hemp concrete was carried out. This allows, on the one hand, to apprehend better the hydric behavior of the different applications of this material, and on the other hand, to promote new economic perspectives for these products. The results showed that this material has a good hydric behavior. The formulation with a high flax shives content showed a moisture buffer value (MBV index) of 2.80, which allowed it to be classified as an excellent moisture regulator. The comparison of the properties of flax concrete with those of standardized hemp concrete showed that both materials are relatively identical with advantageous and satisfactory properties.

Ferhat Benmahiddine, Rafik Belarbi, Abdelkader Tahakourt
Hydration Characteristics of Cementitious Paste with Low Grade Limestone

In limestone quarries, a major portion of limestone is rejected because of the presence of large amounts of impurities that makes cement production difficult. Such limestones have a significant potential to be used for replacing clinker in cement. The use of ground limestone powder as cement replacement has proved to be very promising and has led to several developments in terms of binary and ternary binders. Addition of fine limestone accelerates the initial hydration of cement by providing extra sites for nucleation, in addition to forming new products of hydration like carboaluminates, when there is a reactive alumina source present in the binder. This paper reports a study that was conducted to follow the impact of low-grade limestone on the hydration behaviour of cementitious systems by isothermal calorimetry on paste samples and by compressive strength test of mortar specimens The study was conducted for various replacement levels of low-grade limestone (from two different mines in India) and also for different particle sizes of limestone. Addition of low-grade limestone was found to accelerate hydration in cementitious systems. Acceleration in hydration increased with fineness of limestone and was reflected in compressive strength of mortar cubes as well.

B. Asha, Manu Santhanam
The Resistance of Composite Cement Paste with Calcined Diatomite to Chloride Attack

An experimental study was carried out to understand the resistance of composite cement paste containing different levels of calcined diatomite powder (CDP) to chloride attack. The amount of water used was determined so that the composite cement paste has a normal consistency. The cube specimens with 50 mm size were cast and cured in water for 28 days after which the specimens were immersed in 10% NaCl solution for 1 month and 2 months. The loss in mass and the degradation of compressive strength after 1 and 2 month immersion time were examined. The results show that the CDP cement paste had less surface deterioration compared to Ordinary Portland Cement (OPC) paste. Based on visual inspection, mass loss, and degradation of compressive strength, the composite cement paste with 20% CDP has better resistance to chloride attack.

Muttaqin Hasan, Taufiq Saidi, Rudiansyah Putra, Nurmasyitah
Co-activation of Blended Blast Furnace Slag and Fly Ash with Sodium Sulfate and Hydroxide

The addition of sodium sulfate (Na2SO4) to alkali-activated blast furnace slag (BFS), specifically when sodium hydroxide (NaOH) is used as an activator, allows to reduce the amount of hydroxide necessary to achieve desirable mechanical properties. This kind of activation is suitable for BFS that does not require very high pH to promote its hydration. However, it might fall short in case of hybrid binders such as mix of BFS and fly ash (FA). The objective of this study is to elucidate whether the co-activation with Na2SO4 and NaOH of these blended mixes leads to advantages compared to just NaOH. The effectiveness of such activation on blended systems is evaluated by means of isothermal calorimetry, products assemblage and compressive strength. The FA replacement significantly affects the induction period length, especially when low NaOH concentration is used, leading to poor early age properties. Nevertheless, the obtained results show that, at later ages, it is still possible to obtain mechanical properties suitable for practical application.

Marcello Mutti, Shiju Joseph, Özlem Cizer
Going Below 50% Clinker Factor in Limestone Calcined Clay Cements (LC3): A Comparison with Pozzolanic Cements from the South American Market

Limestone calcined clays are a promising technology as they offer similar performance to OPC from 7 days onwards, while enabling a reduction of the clinker content of 50%. In some regions of the world like South America, pozzolanic cements (i.e., blended cements that combine clinker with natural pozzolans) have been used for decades as an effective solution to reduce the clinker content. Their clinker factors range from 80 down to 60% on average. However, their mechanical properties are in general lower as compared to OPC/CEM I. In this study, we show that by using LC3-type formulations, cements with the same performance as commercial pozzolanic cements can be produced with clinker contents significantly below 50%. This is explained by the high reactivity of calcined clays and the synergetic reaction of metakaolin and limestone that allows offsetting the clinker reduction.

Franco Zunino, Karen L. Scrivener
Microstructure and Durability Properties of Concretes Based on Oyster Shell Co-products

One of the solutions to reduce the environmental impact of the construction sector is the use of alternative materials, more sustainable and with tailored or new properties. This paper proposes the valorization of oyster shell co-products within cementitious materials. These co-products from oyster farm could be used to produce composites with interesting properties. Shell co-products are used in this study to produce load-bearing concretes. These concretes show good durability properties with a lower chloride diffusion coefficient and a higher resistivity compared to references concretes. The optimum mix is composed of CEM III and 50%vol of oyster shell as aggregate. A good cohesion between the particles of oyster shell and the binding matrix is observed, which explains the feasibility to get concretes of mechanical resistance such as the references.

Alexandra Bourdot, Camille Martin-Cavaillé, Marc Vacher, Tulio Honorio, Nassim Sebaibi, Rachid Bennacer
Correlation Between the Reactivity of Supplementary Cementitious Materials and Their Efficacy to Prevent Alkali-Silica Reaction

Supplementary cementitious materials (SCMs) have been extensively used to partly replace ordinary portland cement to reduce concrete carbon footprint and improve concrete durability. However, SCMs with varying reactivities affect the hardened properties and durability of concrete. Current prescriptive specifications to prevent alkali-silica reaction (ASR) are based only on the chemical composition of SCMs and known past performance test results. SCMs with similar chemical compositions but different reactivities will affect their efficacy to prevent ASR. In this study, SCM reactivities were correlated to their ASR prevention efficacy in mortar and concrete mixtures. SCM reactivities were determined based on the calcium hydroxide consumed by SCM at 50 ℃ in a high pH environment. The accelerated mortar bar test and the miniature concrete prism test were used to monitor the expansion and evaluate the efficacy of SCMs in terms of ASR prevention. A very highly reactive fine aggregate and several SCMs including three fly ashes, a slag, a silica fume, and a natural pozzolan with varying compositions were used. The results showed that the reactivity of SCM in the mixture and their mass fraction in the cementitious material blend was correlated well to the expansion of the mortar and concrete mixtures. The findings showed that the higher the SCM reactivity, the lower the expansion due to ASR. A possible new approach to determine the SCM efficacy in preventing ASR was discussed.

Krishna Siva Teja Chopperla, Anuj Parashar, Jason H. Ideker
Water Absorption by Capillarity, Physical and Mechanical Properties of Concrete Containing Recycled Concrete Aggregate with Partial Cement Replacement by Metakaolin

An alternative way to mitigate the impact generated by the Construction and Demolition Waste (CDW) on the environment is recycling this material in order to utilize it as Recycled Concrete Aggregates (RCA) in concrete. Studies carried out demonstrated that while using a scientific mix-design, it is possible to have a Recycled Aggregate Concrete (RAC) with mechanical properties similar the ones in conventional concrete. However, the durability of the recycled concrete is still a matter that should be explored further. The use of Supplementary Cementitious Materials (SCMs), such as metakaolin, has been shown to be efficient when partially replacing cement. It has the ability to improve the packaging of concrete by decreasing the volume of the pores of the material and, consequently, reducing the water absorption capacity of RAC, since RCA presents greater water absorption compared to natural aggregates. Therefore, the aim of this study is to evaluate the durability and mechanical behavior of RAC with 60 MPa of compressive strength by totally replacing the natural coarse aggregate by RCA. Also, part of the cement was replaced by metakaolin. The coarse aggregate considered in this research has 19 mm as nominal maximum size. Total absorption, capillarity absorption, compressive strength test and tensile strength test were carried out for all mixtures. The research results showed that the use of metakaolin offset the increase in capillary absorption in recycled concrete caused by the use of RCA, reaching a value close to concrete with only natural aggregate and without metakaolin for this durability parameter.

Juliano F. Dutra, Lucas C. Menegatti, Mayara Amario, Caroline S. Rangel, Marco Pepe, Romildo D. Toledo Filho
Evaluation of the Potential of Single-Wall Carbon Nanotubes in Improving the Properties of Cement-Composites

The experimental investigation described in this paper deals with the characterization, functionalization, dispersion and use of single-wall carbon nanotubes (SWCNT) in cement-composites. The dispersion of SWCNT was achieved using sonication and modification with a surfactant. The rheological modelling of the SWCNT-surfactant system was carried out, which is shown to reduce the viscosity of the system. In order to better understand the effect of SWCNT in cementitious systems, detailed characterization of the SWCNT and sedimentation tests in water were carried out. To assess the effect on mechanical properties, different loading percentages of the SWCNT were added to the cement mortar, which lead to significant improvement in compressive strength compared to the reference mortar. A threshold dosage range of SWCNT was identified for the optimum mechanical performance of the cement mortar. These results demonstrate the potential of using SWCNT to produce better performing cement-composites.

J. A. Gonzalez-Calderon, Isidro Montes Zavala, Eldho Choorackal, Diego A. Santamaria Razo
Simulating the Hydration Process of Low Water to Cement (w/c) Ternary Pastes Incorporating Superabsorbent Polymers (SAP)

Early age cracking is a high risk for low water to cement (w/c) concrete known as the ultra-high performance concrete (UHPC). The lack of water to fully hydrate cement particles at the early age, provides a rapid increase of self-desiccation and autogenous shrinkage which might lead to cracking. However, internal curing agents such as superabsorbent polymers (SAP) can reduce/eliminate crack development by providing water to the mixture. In this study, a numerical model called CemPP was presented, using a modified version of CEMHYD3D v3 by creating a dedicated pass for the simulation of the hydration process and the microstructure development of low w/c ternary pastes (with silica fume and filler) containing SAPs. Both the filler effect and pozzolanic reaction of silica fume were considered in the numerical simulation, as well as the effect of the water release of SAPs on the hydration process of cement at the early age. The evolution of small pores was lower for SAP pastes than for the reference ones as seen in the experimental results, which indirectly implies lower shrinkage for SAP pastes. The model has been verified to successfully simulate SAP behaviour in cement pastes, and give a good idea about the shrinkage evolution.

Judy Kheir, Benoît Hilloulin, Ahmed Loukili, Nele De Belie
Study of the Pozzolanic Reactivity of Amazonian Metakaolin for Use as a Supplementary Cementitious Material

The application of supplementary cementitious materials (SCMs) as a partial replacement for Portland cement (PC) can significantly reduce carbon dioxide emissions, making the mortar or concrete more sustainable and environmentally friendly. Among the supplementary materials, metakaolin (MK) has received considerable attention, as it provides improvements in mechanical properties and increased durability of the material. The Amazon region presents large deposits of kaolin and therefore this study investigated its use as SCMs. In the study, three metakaolin were produced and characterized using X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XFR), differential thermal analysis (DTA), and laser diffraction techniques. The pozzolanic reactivity study was evaluated by the indirect electrical conductivity method, known as the Luxán Method. In addition, cement pastes were produced, where PC was replaced in the fractions of 40 and 50%, the samples were evaluated by thermogravimetric analysis (TGA) at 28 days of curing. This procedure was adopted to confirm the pozzolanic of MK, by monitoring the reduction of calcium hydroxide. The results show that the wet processing method of kaolin and its calcination at 750 °C for 4 h showed satisfactory results, being sufficiently able to eliminate all the calcium hydroxide at 28 days, confirming the pozzolanic test by the Luxán method.

Ana Paula de Lima Mendes, Daniela Oliveira de Lima, Luciane Farias Ribas, João de Almeida Melo Filho
Evaluation of the Mechanical and Chemical Performance of Mortar Calcined Sludge at 600 ℃ and Nitrophosphogypsum for Its Application in Construction

In recent years, the reuse of industrial waste and by-products have gained relevance within the construction sector. Thereby generating an alternative solution for reducing CO2 emissions originated from Portland cement manufacturing and incorporation processes, finding the optimal dosage that does not affect the mortar properties. This research investigates the effects on fresh and hardened properties in mortar mixtures incorporating two residues as supplementary cementitious materials: nitrophosphogypsum in conjunction with drinking water treatment plant sludge calcined at 600 ℃; characterization of sludge and NPG was carried out. Fresh and hardened properties of seven (7) types of mortar mixtures were evaluated (including a control mixture). Results obtained show the incorporation of these agro-industrial by-products, in conjunction, is recommended as supplementary cementitious material for the preparation of mortar mixtures in dosages from 5 to 10 wt%.

Nemesio Daza, Andrés Guzmán, Yoleimy Avila
Supplementary Cementitious Materials Reactivity: From Model Systems to Concrete

Newly developed reactivity tests for supplementary cementitious materials have shown the ability to quantify reactivity and to differentiate reactive and inert materials. Recent results using the modified R3 test are summarized here. The test uses a model system of supplementary cementitious materials mixed with calcium hydroxide in a simulated pore solution at 50 ℃. Heat release and calcium hydroxide consumption of the supplementary cementitious materials are measured. The reactivity of a large number of conventional and alternative materials has been measured using this test. By using both heat release and calcium hydroxide consumption, two measures of reactivity are obtained, and the test is able to differentiate pozzolanic, latent hydraulic, and inert materials. While the measured reactivity correlates with the properties of cementitious pastes, other factors including the supplementary cementitious material replacement level and the age of testing also influence these predictions. Thoughts on the use of reactivity testing to predict concrete durability are presented.

Prannoy Suraneni
Experimental Studies on the Mechanical Properties of Concrete Made up with Processed GGBS

The current research article presents the utilization and recycling of industrial waste material to help the environment. The production of cement alone contributes 8% of CO2 emissions of global pollution. The article has also enlightened the effectiveness of processed granulated ground blast furnace slag (GGBS) as a supplementary cementitious material (SCM). Processed GGBS replaced the cement with 0–50%, at 5% interval in concrete as a binder. This study also carries the effect of processed GGBS on the fresh and mechanical properties of concrete. The optimization done by the analytical hierarchy process (AHP) shows that the 20% replacement is more effective. This effective utilization of processed GGBS increases the split tensile strength by 15%, flexural strength by 28%, and shear strength by 48%. The overall cost of concrete can be reduced by 8.62% with 20% of processed GGBS.

Sanjay R. Salla, Chetankumar Modhera, U. Raghu Babu
Effect of Mineral Addition LC2 on Shrinkage Produced in Concrete

Together with the additives, the use of Supplementary Cementitious Materials (SMCs) is one of the most sustainable solutions worked on to achieve high performance concretes, more resistant to aggressive environments and as a measure to mitigate different phenomena, such as shrinkage cracks. Mineral additions are one of the most widespread, as they not only favour the partial replacement of Portland cement, but also provide certain chemical and physical properties that make the concrete more durable in different environments. The development of technologies that allow these new materials to appear requires studies to determine their influence on construction. This is why this research is focus on evaluating the effect of the active mineral addition of calcined clay, limestone and gypsum (LC2), on the shrinkage that occurs in fluid concretes and their behaviour in the paste-concrete ratio. Samples P35 (Cement P-35 and Sika Plast additive 0.65%) and LC65 (Cement P-35, addition LC2 30% and Sika Plast additive 1%) are defined. They are evaluate by means of chemical shrinkage in cement pastes and then a study is made of the shrinkage in the concretes by means of ASTM c-157 and the shrinkage channel. This research demonstrates the shrinkage reducing effect of the mineral addition LC2 and achieves an important step forward in the sustainable development of new materials for the Construction Industry in Cuba.

María B. Díaz García, Yosvany Díaz Cárdenas, José F. Martirena Hernández
Formulation of Expansive Mortars Based on Calcareous-Based Additives and Ternary Cement with Calcined Clay and Limestone

The present work deals with the evaluation of the addition of a calcareous-based expansion additive in formulations of type III mortars, consisting of Portland cement, LC2 and stone powder as aggregate, to obtain expansive mortars. The design of the experiment was carried out in order to evaluate the influence of the calcareous-based expansion additive on masonry mortars with mineral addition LC2, following the criteria established in NC 175: 2018 “Masonry mortars - specifications”.

Dania Betancourt-Cura, Fernando Martirena-Hernandez
Data Mining Strategies to Handle State of Art Knowledge on Self-healing Capacity of Cementitious Materials

Concrete and cement-based materials inherently possess an autogenous self-healing capacity, which is even high in High and Ultra-High-Performance Concretes because of the high amount of cement and supplementary cementitious materials (SCM) and low water/cementitious material (w/c) ratio. Despite the huge amount of literature on the topic self-healing concepts still fail to consistently enter design strategies to effectively quantify their benefits on the structural performance. In this study, quantitative relationships have been developed through design charts and artificial neural network (ANN) models. The employed approaches aimed at establishing a correlation between the mix proportions, exposure time, the width of the initial crack, and volume of fibers against suitably defined self-healing indices (SHI), quantifying the recovery of material performances which can be of interest for intended applications. Therefore, this study provides, for the first time in the literature to the authors’ knowledge, a holistic investigation on the autogenous self-healing capacity of cement-based materials based on extensive articles focused on the literature data mining. The design charts are developed to pave the way towards consistent incorporation of self-healing concepts into durability-based design approaches for reinforced concrete structures, aimed at quantifying, with reliable confidence, the benefits in terms of slower degradation of the structural performance and extension of the service lifespan. Finally, through ANN, a straightforward input-output model is developed to quickly predict and evaluate the self-healing efficiency of cement-based materials which can significantly reduce, in the design stage, the time, money, and efforts of laboratory investigation.

Shashank Gupta, Salam Al-Obaidi, Liberato Ferrara
Carbonation Results in Diverse Cement Pastes with 10% Substitution of Binder by Bentonite

The greenhouse effect is accelerating to reduce environmental footprint of concrete. In addition to the traditional mineral additions which are blast furnace slags, pozzolans and fly ashes, worldwide are tested new products in order to have a wider variety of substances capable of maintaining the performance and good durability of the concrete. Among these substance, calcined clays are proposed due to their availability in numerous places. However, the pre-calcination ads waste of energy and therefore the use of non-calcined clays appears as a possibility very little explored, as few literature references are found. In present work non calcined bentonite has been tested by substituting 10% of different Portland cements. Paste specimens have been submitted during 3 and 6 months to natural carbonation in three different exposures: indoors and outdoors sheltered and unsheltered from rain. The results show that the presence of bentonite either improves the carbonation resistance or does not modify it. With respect to the resistance to chloride ingress, the tests have been in mortar in accelerated conditions through an electrical field. The results indicate that the presence of bentonite also resulted beneficial.

Carmen Andrade, Ana Martinez, Miguel Ángel Sanjuan, José A. Tenorio

Durability and Life Cycle Assessment in Urban and Marine Conditions

Expanded Clay as Bacteria Cells Protector in Manufacturing Self-healing Mortar: The Possibility of Adding Less Nutrient to Maintain the Mechanical Properties of Mortar

Bacteria-based self-healing is a promising method due to its effectiveness to completely heal the crack. Expanded clay was chosen as a bacteria protector as it can retain a high amount of bacteria liquid in its pores and it is compatible with the mortar matrix. Most researchers employed bacteria in the form of spores to produce self-healing concrete due to its survivability in a harsh environment. However, to activate the spores, yeast extract, which has a negative effect on mortar strength, needs to be added. In this research, Bacillus sphaericus (BS) vegetative cells were used as a healing agent to determine whether these cells survive in the mortar and could precipitate CaCO3. The variation in the amount of yeast extract as a bacteria nutrition was also investigated. The mechanical properties of fresh and hardened mortar, such as flow, compressive strength, and bulk density, were determined. The healing efficiency was observed through crack closure observation. In the end, the morphology of CaCO3 precipitation was observed under a scanning electron microscope (SEM). The result shows that it is possible to remove yeast from the mixture when producing self-healing concrete with vegetative cells as a healing agent. The resulting mortar’s mechanical properties are similar to the reference, and the healing efficiency was still acceptable.

Puput Risdanareni, Jianyun Wang, Nele De Belie
Comparative Life Cycle Assessment of Concrete with Coarse Natural and Recycled Concrete Aggregates for Household Construction, Case Study in the Hamburg Area

Society’s awareness of sustainability has been increasing in the last years, hence the use of recycled materials is becoming crucial in order to avoid negative impacts of human activities on the planet. Concrete is one of the most important building material in the construction industry. For the sake of concrete sustainability, the introduction of recycled concrete aggregate (RCA) in new concrete represents a possibility of avoiding construction waste and saving resources. The aim of this study is to evaluate the environmental impacts of three different sources of coarse aggregates for concrete production through a comparative Life Cycle Assessment (LCA). Two aggregates are produced with recycled construction and demolition waste, also known as RCA, and the third is produced from natural gravel also referred as natural concrete aggregate (NCA). The analyzed products are several concrete mix designs, covering different strength classes which are commonly used for household construction. The level of RCA replacement for the mix designs were established to a German guideline. The processes and materials evaluated comprehend the concrete production in a ready-mix plant located in Hamburg, Germany. Based on a data collection from the literature and different datasets out of the databases Ecoinvent version 3.7 and ELCD version 3.2, a LCA-Model has been developed. The results are presented using five midpoint indicators calculated by the CML-baseline and ReCiPe Method. During the evaluation of the LCA-results, it was found that the inclusion of RCA does not inevitably reduce the environmental impacts of concrete. Depending on the considered impact categories, it is possible that additional strains are eliminating the emerging benefits of RCA contribution. Supplementary transportations, changes in the mix design, compressive strength, and general demands for recycling old demolition waste are in focus of the discussion. In order to improve the sustainable performance of RCA in concrete some factors need to be considered.

Lionel Reichart, Juan Cassiani, Sylvia Kessler
Deformations in Pastes During Capillary Imbibition and Their Implications

In capillary imbibition (or absorption) experiments performed on cementitious materials, a non-linear evolution of water uptake with the square root of time is frequently reported. This anomaly is derived from analytical methods that assume that the pore structure remains invariable during water ingress. A more comprehensive understanding of the transport phenomena should consider calcium silicate hydrate (C-S-H) swelling during water ingress. Such swelling may cause changes in the pore structure and interferes with water uptake. To analyse that process, the external deformations occurring in cement paste samples during capillary imbibition tests were measured. Pastes were prepared using Portland cement (CEM I 52.5 N) and water/binder = 0.4 and 0.6. After 7 days of curing, strain gauges were glued on the samples to register the external strain. Differences in the deformation results show that the restriction of the system plays an important role. Results indicate that the anomalous water ingress during capillary imbibition coincides with the measured external deformations. In this sense, calculations based on the model of Thomas and Jennings showed that pores shrink. Such pore changes are synchronous with the capillary rise. Hence, an improved description of the delaying process in the transport mechanism is here presented considering the effects of the changing pore structure. The extent of this physical effect is related to the porosity and amount of non-deforming and deforming phases (C-S-H) of each system.

Natalia Alderete, Yury Villagrán Zaccardi, Nele De Belie
Repair of Concrete in Environments with Chlorides or Subjected to Freeze-Thaw Scaling

Crack formation further decreases the durability of structures when chloride ions associated with freezing temperatures are present. Therefore, preventing the entry of aggressiveness is imperative to guarantee the service life. Repair actions might recover the liquid-tightness when cracks occur. A water repellent agent (WRA) and a sodium silicate (SS) solution were applied to self-repair cracks in the current research. The repair occurred by manual injection of cracks to obtain a proof-of-concept for the possible self-healing efficiency. Two extreme conditions have been assessed after the healing period, the first referring to continuous immersion in a chloride solution, and the second applying freeze-thaw conditions with de-icing salts. Chloride ingress was evaluated through the colour change boundary test. In addition, optical microscopy analysis was used to measure the crack width and to observe differences before and after exposure. SS prevented the chloride ingress through the crack in both conditions. However, the method used to verify chloride ingress did not give consistent results for the WRA due to its hydrophobicity. Microscopic analysis showed that both agents could avoid chloride ingress in the cracks. For the samples exposed to freeze-thaw cycles, only chloride ingress measurement could indicate the healing performance as the scaling destroyed the surface.

Vanessa Giaretton Cappellesso, Tim Van Mullem, Elke Gruyaert, Kim Van Tittelboom, Nele De Belie
Influence of Self-healing via Embedded Macrocapsules Filled with Polyurethane on Carbonation of High-Volume Fly Ash Mortar

During carbonation of concrete, calcium hydroxide is consumed which results in a drop of the pH which can cause steel corrosion. In uncracked cementitious materials it can take several years before the carbonation front reaches the level of the reinforcement. However, most structures are cracked allowing for a fast ingress of carbon dioxide at the cracks. Self-healing cementitious materials are able to close cracks without a manual repair intervention. Most of this research has focused on a regain in liquid tightness or strength, yet results on the influence of carbonation are scarcely reported. In the current study, High-Volume Fly Ash mortar samples were made with pre-placed glass macrocapsules filled with polyurethane. Three different series were studied: reference specimens, specimens with non-pressurized capsules and specimens with pressurized capsules. After cracking of the specimens, the self-healing efficiency was assessed via a capillary water absorption test, prior to placing the specimens in a carbonation chamber and studying the carbon dioxide ingress at the location of the crack. The specimens with non-pressurized capsules showed a sealing efficiency of more than 80% compared to only 25% for specimens with pressurized capsules. The capsules were pressurized by mixing the polyurethane with benzoyl peroxide. This most likely resulted in a premature polymerization of the polyurethane inside some capsules, preventing a good crack filling. Nevertheless, the carbonation front was less deep at the location of the crack compared to the reference series without capsules. The specimens with non-pressurized capsules had a good performance; on average the carbonation depth at the location of the crack was only half of that of reference specimens.

Tim Van Mullem, Arne Sintobin, Philip Van den Heede, Laurence De Meyst, Robby Caspeele, Nele De Belie
Reliability Analysis for Service Life of Concrete Structures Subject to Various Carbon Dioxide Concentrations

Carbonation is one of the factors that can reduce the service life of reinforced concrete structures, especially in urban environments where carbon dioxide (CO2) concentrations are elevated. While concrete is generally considered to be resistant to carbonation under normal atmospheric conditions, in polluted urban environments and accelerated laboratory conditions, carbonation can occur at accelerated rates. Concentration of carbon dioxide (CO2) can have a significant impact on the rate at which carbonation occurs. There are no current guidelines for determining the carbonation rate in reinforced concrete as a function of CO2 concentrations. This work presents a risk-based framework that can be used to quantify carbonation depths and rates for various levels of CO2. This paper also identifies the key variables that affect the service life of reinforced concrete structures, from the point of view of carbonation and the resulting corrosion. These variables include the quantities of the various hydrated/anhydrous phases and the effective diffusion coefficient of the cementitious system. Monte-Carlo simulations are also performed to identify the change in time to carbonation with change in both CO2 concentration exposure and the concentrations of the hydrated and anhydrous phases of concrete.

Gokul Dev Vasudevan, David Trejo
Durability Analysis of Ultra High-Performance Fiber Reinforced Concrete Structures in Cracked Serviceability Limit State

Ultra High Performance (Fibre Reinforced) Concrete and Cementitious Composites (UHPFRCCs) have not only the potential to control the crack width but, even better, the potential ability to spread a damage state into a set of multiple tiny and tightly spaced cracks in the strain hardening regime, which would otherwise localize into a single crack. This is extremely advantageous for durability since the governing parameter is the opening of the single crack. Within the framework of the H2020 ReSHEALience project, one of the main objectives is to upgrade the concept of Ultra High Performance Concrete (UHPC) structures to Ultra High Durability Concrete (UHDC) structures, by implementing micro- and nano-scale constituents, which stimulate the autogenous self-healing capacity of concrete. From 4-point bending tests on UHDC 30 mm thick beams, it was observed a sequential cracking behaviour with evenly distributed spacing, which also resulted into a deflection and strain-hardening behaviour. In this paper, based on material identification test data, a sectional analysis of UHDC structural elements has been performed taking into account the sequential cracking behaviour and, from the sectional analysis, the member displacement behaviour was evaluated. Degradation mechanism governing laws, referring to penetration of chlorides and sulphates, have then been incorporated into the aforementioned structural design algorithms, in order to predict the long-term serviceability flexural behaviour of UHDC structures under structural service scenarios characterized by extremely aggressive conditions. The results are being validated against experimental monitoring of a real scale basin for collecting water from a geothermal power plant made with selected UHDC mixes.

Salam Al-Obaidi, Fabio De Sandre, Liberato Ferrara
Investigating the Use of Off-Specification Ashes to Prevent Alkali-Silica Reaction

Two fly ashes and one milled bottom ash that do not meet standard specification requirements per ASTM C618 (commonly termed as off-spec) were investigated for their use in preventing alkali-silica reaction (ASR). The ashes were characterized for their chemical composition, pozzolanic reactivity, and particle size distribution. A very-highly reactive fine aggregate was used in this study. The accelerated mortar bar test (AMBT) was done at two different replacement levels of 25% and 50% of ordinary portland cement (OPC) using the off-spec ashes. The AMBT results showed that only one mixture was able to prevent deleterious ASR. Also, the mixture with 25% ash had a high sulfate content showed higher expansion than the control (100% OPC) mixture. The miniature concrete prism test (MCPT) was also used to evaluate this mixture for up to 56 days. Further, the mixtures were investigated to differentiate ASR expansions and the potential for other deleterious chemical reactions from alkalis and sulfates in the ashes. The results of this study highlight the need for supplemental test methods to standard ASR accelerated test methods to evaluate the efficacy of off-spec ashes for ASR prevention.

Anuj Parashar, Krishna Siva Teja Chopperla, Jason H. Ideker
A Review on Durability Performance of Calcined Clay Binders for Adoption in the Construction Industry

Calcined clays are considered one of the most promising sources of supplementary cementitious materials (SCMs) for substituting Portland clinker in the production of concrete. Natural clays have been extensively studied for optimizing pre-conditioning treatments to increase their reactivity, and consequently the hydration, and mechanical properties of low energy binders produced with them. Studies on durability performance are essential for providing the confidence required for the widespread adoption of calcined clays as SCMs. This paper analyse the suitability of calcined clay containing binders in different exposure environments to facilitate its adoption, and presents a brief overview of durability performance of cementitious materials produced with kaolinitic or non-kaolinitic calcined clays. Also, the research needs that will facilitate the adoption of calcined clays in construction projects, as well as the physico-chemical alterations introduced by calcined clays in the hydrated cement matrix is discussed.

Yuvaraj Dhandapani, Susan A. Bernal
Estimating Service Life of Prestressed Concrete Systems Exposed to Chlorides

In general, pretensioned concrete (PTC) structures are being designed with a target service life of about 100 years. However, cases of premature/catastrophic corrosion-induced strand failures have been reported. This necessitates a re-examination of the current practices for service life-based design (SLD) as well as corrosion assessment of new and existing PTC structures respectively, especially the choice of limit states and the parameters considered. The work presented in this paper is a component of the research carried out to develop tools to assist SLD and assessment of PTC structures, and focusses on the estimation of time required for Passive-to-Active (P-to-A) transition, which is the first step of chloride-induced corrosion of prestressed steel strands. For this, ordinary Portland cement-based reinforced mortar specimens (both unstressed and stressed categories) were prepared using prestressing (PS) steel king wires extracted from 7-wire strands. Totally, 10 specimens (5 + 5) were cast, cured for 28 days and then subjected to dry-wet (5-day drying followed by 2-day wetting) cycles in simulated concrete pore solution containing sodium chloride. The P-to-A transition was detected by continuous monitoring of the open circuit potential and impedance measurements at the end of every wet exposure period. The specimens were then autopsied and the concentration of chlorides in the mortar at the level of steel was determined and defined as Clth. It was found that the Clth of PS steel can reduce by half in OPC system when prestress is applied. A case study was performed to understand the implications of using overestimated values of Clth on the service life. An overestimation in service life of about 40% was observed when the Clth of unstressed PS steel was used - emphasizing the importance of determining the Clth of stressed steel and using it for service life estimation.

Dyana Joseline, Radhakrishna G. Pillai
Relationship Between the Vertical Profile of Marine Aerosol Salinity and the Chloride Accumulation into Concrete

This paper analyses the influence of height from the ground on the vertical distribution of marine aerosol salinity. It considers altitudes between 1.5 and 10 m from the ground in a region under the major influence of surf produced aerosol and its impact on chloride accumulation into concrete along time. Results show that the rate of chloride deposition on wet candle markedly decreases when the altitude increases and this relationship can be represented by a power decay function. The impact of the salinity decrease with altitude on chloride accumulation into concrete is significant and can surpass the level of 50% after 50 years of exposure. As a consequence, this behaviour should be considered when analysing the performance of vertical concrete structures placed in marine atmosphere zone.

Gibson Meira, Pablo Ferreira
Effect of Size and Preconditioning of Concrete Cores Against Sulfate Attack (Test)

Some of the proposed accelerated tests for evaluating the sulfate resistance of concrete address only the Portland cement, as the hydrated cement paste contains unstable compounds that may react with sulfate ions, while others are based on concrete performance. In search of comprehensive and practical assessments, some researchers proposed the evaluation of core samples as performance tests. The kinetics of attack is accelerated by further exposing the inner matrix of the concrete to the aggressive solution. Another accelerating strategy reported in the literature is to precondition the samples by vacuum saturation with sulfate solution, which speeds up the penetration of sulfate ions into concrete at the start of the test.In this work, both strategies were applied to develop an accelerated performance test for concrete. Core specimens of two sizes were drilled off from two concrete types and exposed to a highly concentrated sulfate solution. Two preconditioning procedures were applied to the samples prior to exposure. The results show a large reduction in failure time when a vacuum step is used as preconditioning (one-sixth). This methodology could be useful in recycled concrete production to evaluate the potential reactivity of source concrete against sulfates.

Lautaro R. Santillán, Yury A. Villagrán-Zaccardi, Edgardo F. Irassar, Claudio J. Zega
CFRP Reinforcement for Historical Buildings at Mexico City: Concrete Frame Structures Around 1940 to 1960

Around 1940 the introduction of skyscrapers improved the development of reinforced concrete systems capable of adapting to seismic, soil, and subsoil conditions. Nowadays, most of them still operative as iconic historical constructions. Nevertheless, they exhibit differential subsidence considering their age, natural aging, and seismic activity; then, they require an analysis to deem them safe structures according to codes demands. Furthermore, because of the historical value of those buildings, it is necessary to reach the structural adaptation without disturbing its integrity. To accomplish these purposes, the use of FRP materials, focus on carbon fiber was considered. This paper aims to present the results of the fiber influence to control plastic flow and its effect on the ductility of structural members by bending tests to study the distribution of the internal forces.

Juan Manuel García Garduño
Role of Oxygen and Humidity in the Reinforcement Corrosion

Corrosion of reinforcement is produced when the carbonation front or the chloride threshold reaches the surface of the steel bars. The carbonation progresses when the concrete pores are not filled with water being prevented when these pores are highly water saturated. In the case of chlorides, reversely, the penetration is slower if the pores are not saturated, being negligible if the relative humidity is low. Degree of concrete saturation plays then a crucial role in the advance rate of the aggressive fronts. In addition to water, oxygen plays as well an important role in the steel depassivation stage. In carbonation case, oxygen is available as the pores are not filled with water, while in the case of the chlorides is the opposite and the amount of oxygen is that dissolved in the pore solution. In the stage of corrosion propagation, the oxygen is much less critical due to the autocatalytic nature of the corrosion, being however the humidity an essential element. These aspects will be commented and illustrated with results. The correct interpretation of the role of humidity and oxygen is an essential element in the assessment of existing structures.

Carmen Andrade
Experimental Investigation on the Influence of Partial Immersion and Drying Cycles on Hemp Concrete Properties

The construction sector has a significant environmental impact, since it is the largest energy consumer and is responsible for 25% of greenhouse gas emissions. Vegetal concretes represent a good alternative to reduce the environmental footprint of building materials, because of their thermal insulation properties and the use of vegetal waste. In addition, they have the outstanding environmental quality of being carbon negative. Hemp lime concrete is the most used bio-based material in building sector and its potential as an environmental-friendly material was quickly realized. It is a relatively new building material and its use is limited by the lack of data concerning its durability and the evolution of its properties over time.This paper focuses on the influence of an accelerated aging of hemp lime concrete on its hydric and thermal properties. Samples will undergo several cycles of partial immersion and drying and will be characterized before and after the accelerated aging. Partial immersion was preferred to complete immersion, as it is more representative of the real climatic conditions. The thermal conductivity and the capillary absorption coefficient will be determined. Microscopic observations of the surface topology will also be carried on, in order to evaluate the microstructure alteration.

M. Maaroufi, A. Bourdot, M. El Assaad, K. Abahri
Sustainability and Economic Viability of Self-healing Concrete Containing Super Absorbent Polymers

Recent studies highlighted the need to investigate the sustainability of innovative cement-based composites. In this regard, some works focused their attention on the use of Super Absorbent Polymers (SAPs) blended into the concrete matrix also employed to promote the autogenous healing, which can result into extended durability. In this study the Life Cycle Assessment (LCA) methodology takes into account the impacts associated to the whole service life of a structure. Thus, the eco-profile of a wall made up of concrete containing SAPs, was compared to the one of a reference wall without those additions. Four scenarios were considered to estimate the frequency of the repairing activities needed because of the chloride induced corrosion. Two corrosion models were adopted: a uniform one for scenarios 1 and 2, with a service life of 50 and 100 years respectively and the hemispherical pit model, for scenarios 3 and 4 with 50 and 100 years of service life as well. Additionally, a Life Cycle Cost (LCC) analysis was developed to investigate the overall costs. The results highlight the better performances for SAP-containing concrete with a reduction up to 11% for the overall costs and up to 55% for the environmental burdens.

Davide di Summa, Didier Snoeck, José Roberto Tenório Filho, Philip Van den Heede, Sandra Van Vlierberghe, Nele De Belie, Liberato Ferrara
Self-healing Capabilities of Ultra-High Performance Fiber Reinforced Concrete with Recycled Aggregates

This study examines the effect of recycled aggregates on the stimulated autogenous self-healing of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) when exposed to wet and dry conditions. Recycled aggregates have been produced by crushing four months old UHPFRC specimens with an average compressive strength of 150 MPa. Two different percentages (50% & 100% by weight) of recycled aggregate (0–2 mm) have been used as a substitute for the natural aggregate in a reference UHPFRC mix to produce recycled UHPFRC. After an assessment of the overall mechanical properties of the recycled UHPFRC mixes, one year old notched beam specimens were pre-cracked to the width of 150 µm through a three-point flexural test. The self-healing capacity of recycled UHPFRCs has been investigated in terms of water absorption tests, regain in flexural strength and microscopic crack healing, at scheduled times after pre-cracking (0 days, 1 month, 3 months and 6 months). Constant wet/dry healing conditions were maintained throughout the experiment. The specimens with recycled UHPC aggregate showed better and longer self-healing than the specimens with natural aggregate, which provides additional value to the overall environmental sustainability of the investigated category of materials.

Niranjan Prabhu Kannikachalam, Ruben Paul Borg, Estefania Cuenca, Nele De Belie, Liberato Ferrara
Environmental Impact of Calcium Sulfoaluminate Cement Manufacturing: An Indian Case Study

Ordinary portland cement (OPC) manufacturing contributes to about 5–8% of the CO2 emissions globally and its consumption is expected to increase. Finding alternative to OPC is a global issue in the recent times. Calcium sulfoaluminate (CSA)-based binder is gaining attention due to the lower requirement of limestone and temperature requirement during its production. There are several lab-scale studies where CSA has been produced using different alternative raw materials. In this study, earlier research works were reviewed to understand the different types of raw materials used to produce CSA. The data for cement production was collected from a cement plant in India to conduct a life cycle assessment (LCA). Two hypothetical cases of CSA production were assumed in the same cement plant, and environmental impacts were calculated in terms of CO2 emissions and energy consumed. It was found that with the change in alternative raw materials, the impact could vary from 460 to 590 kg CO2 per tonne of CSA. Generally, 30–45% of CO2 emissions reduction was observed when compared to Portland cement, whereas the substantial change in energy consumption was not evident. Transportation distance of raw materials seemed to be critical with respect to energy consumed.

Atul Sharma, Anusha S. Basavaraj, Piyush Chaunsali, Ravindra Gettu
Sustainability Assessment of Concrete Pavements with Recycled Concrete Aggregate

In the past decade, increasing attention has been given to paving the roads with concrete mixtures due to their numerous advantages over bituminous roads. Further benefits could be expected by incorporating recycled-concrete aggregates from demolition waste (DRCA) in concrete pavements. In the present study, life cycle assessment (LCA) is used as a tool to illustrate the calculation of the environmental impacts of concrete pavements made with DRCA and comparison with those of conventional concrete pavements, for both low- and high-volume applications. It was found that, for mix designs taken from the literature, the replacement of natural coarse aggregates with DRCA for high-volume roads could result in an increase in the environmental impacts (CO2 emission and embodied energy) whereas the impacts could be similar for low-volume roads.

J. Jayasuriya, Anusha S. Basavaraj, Surender Singh, Ravindra Gettu
Characterization and Economic Viability of Local Sugarcane Bagasse Ash as Partial Replacement of Portland Cement

Portland cement is one of the most consumed materials in civil construction, however, there is a large emission of CO2 in cement production, therefore the search for alternative materials that reduce environmental impacts and production costs arises. As Brazil is one of the main world producers in the sugar and alcohol complex, sugarcane represents a great importance of agribusiness in the country's economy. Bagasse is a sugarcane by-product which, during burning in boilers, generates sugarcane bagasse ash (CBCA). The objective of this research is to evaluate the mechanical properties and the influence of partial replacement of local CBCA in proportions of 10%, 15%, 20% and 0% as a reference. For durability analyses, specimens were made and analyzed by electrochemical techniques for corrosion assessment, through the test of corrosion potential (Ecorr), corrosion intensity (Icorr), resistivity of concrete and resistance to linear polarization. The mineralogical composition was evaluated using XRD analysis. Regarding the economic feasibility, bibliographic surveys were carried out for a better basis and findings of the research. The results indicated that the specimens produced with CBCA reached more electronegative corrosion potential values over time, providing a more favorable condition for corrosion. Concluding that the physicochemical characteristics of the local ash depend on the granulometry, degree of crystallinity of the bagasse fibers, burning conditions and that the ash has great availability and can replace cement in low contents with significant advantages.

Ennes do Rio Abreu, Eliana Cristina Barreto Monteiro, Pedro Castro Borges
Effect of Combined Action of Carbonation and Bending Load on Mortar

Carbonation is a pathology that affects the majority of concrete structures as they are exposed to the ambient air and consequently to the carbon dioxide present in the air. In addition, these structures may be subject to mechanical stresses over time. The main objective of this research is therefore to investigate the effects of carbonation on the mechanical strength and conversely the effects of mechanical stress during the accelerated or natural carbonation process. Therefore, within the framework of Rilem TC 281-CCC working group 4, the coupling of accelerated carbonation and mechanical loading of Portland and slag cement based mortars has been studied. The impact of accelerated carbonation on the different properties of the mortars (porosity, masses, etc.) was also studied.The results show a slight increase in the depth of carbonation on the mortar under tensile stress and a slight decrease in the depth of carbonation for the mortar under compressive stress.

Elodie Piolet, Siham Kamali-Bernard
Concrete Beams with Steel Reinforcement Subjected to Fractions of Yielding Strength Under Accelerated Corrosion Tests

The objective of this work was to verify that tensile stresses at 40% and 80% of the corresponding yielding strength are not structurally influenced by the level of corrosion under accelerated tests. One of the main concerns when having corrosion of reinforcing steel is the sustaining stress level before non-reversible corrosion damage. Eight reinforced concrete beams (15 cm × 30 cm × 350 cm) were designed by using local crushing aggregates with a water/cement ratio (w/c) of 0.62. Accelerated corrosion was applied to the tensioned longitudinal reinforcing steel bars by contaminating the concrete during the mixing process and later with wetting and drying cycles. A four-point bending load test setup was used to the posttensioned beams in pairs and simulating sustained loads. The loads were applied until reaching the tension stresses in the longitudinal reinforcing steel bars at 40% or 80% of the yielding strength of the bars. It was concluded that the average loss of the beam stiffness after flexural cracking was 76%. Few changes were observed in the corrosion potentials for those beams, then the tensile stresses at 40% and 80% of the yielding strength do not influence the corrosion potential level measured at the ages, materials and conditions tested.

Rebeca Visairo-Méndez, Jorge Varela-Rivera, Pedro Castro-Borges
Electrochemical Behaviour of Steel Embedded in Alkali Activated Metakaolin/Limestone Based Mortar

The electrochemical behaviour of steel reinforcement was investigated as embedded in mortars based on alkali activated binders of metakaolin (MK)/limestone (LS) precursors with mass ratios of 100/0, 70/30 and 40/60, selected from previous studies of optimization and modeling of formulations, gel composition and molecular structure, as well as environmental aspects of these materials. A three electrodes arrangement and the polarization resistance technique were used to obtain the current density (Icorr) and the half-cell potential (Ecorr) of the embedded steel for up to 156 days of curing under laboratory conditions. The embedded steel embedded remained in the passivation zone from the beginning of the study according to the criteria of Icorr used for portland cement-based materials. The incorporation of LS into the MK precursor showed a beneficial effect in the electrochemical behavior of the steel embedded, the mortar with a binder of 70/30 (30% LS) showed the best performance at 156 days of curing, with values of Icorr below 0.005 µA/cm2, representing an innovative and suitable alternative to 100% metakaolin based geopolymers. On the other hand, the results showed that Icorr seems to be a better indicator for the condition of the steel embedded than Ecorr in the mortars analyzed.

F. R. Vazquez-Leal, J. M. Mendoza-Rangel, C. Andrade, P. Perez-Cortes, J. I. Escalante-García

Additive Manufacturing in Concrete Construction

Additive Manufacturing in Architecture: 3D Printing Solutions for Vaulted Spaces

Additive manufacturing (AM) will change architecture. Nowadays a trained digital designer can control both digital and physical tools for the development of a project.The starting point of this research is Najaat, a project for an entire 3D printed village in Syria inspired by other case studies like GAIA. The project is part of a larger study about self-made architecture and materials such as raw earth, straw, rice husk and hydraulic lime which make it reusable, recyclable and affordable. The shapes chosen for Najaat are organic and easily adaptable to any environment, highlighting the total freedom that the 3D printing system allows. At the same time these geometries are also aimed at challenging the limits of 3D printing by working on the maximum projection.This paper focuses on the possibility to print closed domed spaces using only common printing machines instead of robotic arms, in order to keep the process both economic and ecological. The printing process refers to the theory of Nubian vaults, which are structures built without supports exploiting the inclination of bricks layers. A scaled prototype of a dome has been printed through a hybrid system of layers, that helped the structure non to collapse on the top. The result still shows some imperfections due to some limitations of the machine, but it is useful to demonstrate that some typical problems of excessive overhang can be overcome through a deep study of the material itself, of the geometry and also of the printing path.

Angelo Vito Graziano, Ilaria Cavaliere, Dario Costantino, Giuseppe Fallacara, Nicola Parisi
Understanding the Structural Build-Up Rate of Cementitious Materials for 3D-Printing

The concrete 3D-printing technology is highly dependent on the material’s rheology and on the deep understanding of how those properties evolve with time. This evolution occurs due to reversible structural build-up and irreversible chemical phenomena, like hydration reactions. To guarantee structural stability of the printing process, the material, as soon as it is deposited, needs to build-up an internal structure to withstand its weight and the weight of the following layers. Therefore, the static yield stress and how it increases over time at rest becomes of first interest. The concrete structural build-up happens due to both CSH bridge formation by nucleation of cement grains at their pseudo-contact points during the dormant period of hydration, and flocculation due to colloidal interactions. The currently accepted knowledge on the subject relates the yield stress growth with the structural build-up rate of the material through different models, as it also uses different measuring protocols and assumptions to its determination. The goal of this research is to summarize the literature on this topic, identifying the similarities and discrepancies in the available data to further propose a more suitable approach to evaluate this parameter. To do so, a systematic review was carried out in the Web of Science database with appropriate keywords. Then the data were organized and analyzed taking into account aspects such as the definition of structural build-up, the model used, simplifications/assumptions of the model, experimental protocol, mixture parameter and model limitations.

Luiza R. M. Miranda, Karel Lesage, Geert De Schutter
Interlayer Bond and Porosity of 3D Printed Concrete

Extrusion-based concrete 3D printing is being increasingly investigated for its application in the construction industry. Having a layer-wise extrusion process could impart a lack of fusion between the layers due to drying and moisture migration between the layers, resulting in higher porosity and weak interlayer bond strength. This paper presents a study to understand the effect of fresh cement paste applied in between the two layers on the porosity and bond behaviour of samples printed at a relatively high interlayer time gap of 15 min. Two different types of 3D printable mixtures were considered in this study: (i) a Portland cement-slag binary blend mixture and (ii) a calcium sulfoaluminate cement-based mixture. Two-layered wall elements were printed with a constant 15 min interlayer time interval. The interlayer bond strength was determined by pull-off tests and compared among the different mixtures with and without a Portland cement-based paste applied between the layers. Also, the porosity of the printed elements was studied with mercury intrusion porosimetry. The results indicate that the total porosity and critical pore diameter decrease with the application of the fresh cement paste. Also, the bond strength increases slightly with the application of cement paste as it reduces the total porosity of the samples.

Manu K. Mohan, A. V. Rahul, Geert De Schutter, Kim Van Tittelboom
Adhesion Performance of Cement-Based Materials in the Fresh State

Cement-based materials placed onto a substrate must achieve sufficient adhesion at the interface to avoid detaching, especially for the overhead positions. Previously, more attention was paid to adhesion in the hardened state, while the adhesive properties of fresh cement-based materials were rarely studied. In this paper, a tack test was used to evaluate the adhesion of fresh cement-based materials. The influence of two aspects including the loading rate and the substrate surface roughness was investigated. Results indicated that the loading rate (varied from 0.01 to 0.08 N/s) had a limited effect on the adhesion of fresh cement-based materials. However, an increase in the substrate surface roughness resulted in a reduced adhesive strength in the fresh state.

Yaxin Tao, Karel Lesage, Kim Van Tittelboom, Yong Yuan, Geert De Schutter
A Study of Early Age Shear Properties of 3D Printable Cementitious Mixes with Fiber Reinforcements

The use of Fiber Reinforcement in digitally manufactured concrete is not only one of the viable techniques in the otherwise difficult reinforcement strategy but also a segue to the use of highly durable Ultra High Performance Concretes in 3D printing. For this, the characterization of early age mechanical properties such as tensile, shear and compressive strength of printable Fiber Reinforced Concrete is very important in the design process. The printability of fresh concrete which is defined as combination of pumpability, extrudability and buildability can be characterized using the tensile strength of filament, the shear strength and the compressive strength of the freshly printed element. This study aims on defining the shear strength of 3D printable cementitious mortars at early ages focusing on the “printability window” highlighting the phase transitions in printed concrete. Highly cohesive mortar with high Sulfo-Aluminate cement content is cast with Basalt fibers in specially designed molds to understand these said properties at various times from casting namely, 30, 45, 60 and 90 min. Repeatability of the methodology has been established using 3 iterations of each experiment and crack - failure patterns have been studied closely. Further study on developing the Kupfer’s failure envelopes is underway by including the compressive strength study obtained through penetration tests and tensile strength study.

Sriram K. Kompella, Andrea Marcucci, Francesco Lo Monte, Andrea Bassani, Stefano Guanziroli, Marinella Levi, Liberato Ferrara
Influence of Crystalline Admixtures and Bacteria on the Fresh Properties of Self-healing Concrete

Concrete is undeniably susceptible to cracking due to its low tensile strength in spite of its ability to withstand high compressive stresses. Cracks may jeopardize the concrete core and reinforcements due to the ingress of water and aggressive substances. A promising technique to effectively seal cracks in hardened concrete is using a self-healing technology by introducing healing agents to the fresh concrete mixes. Crystalline admixtures and bacteria emerge as promising self-healing agents to promote stimulated autogenous healing and autonomous healing mechanisms, respectively, improving simultaneously the durability of the concrete. Healing agents are mostly added on top of the normal mix without changing the mix design of the concrete, while in fact, it may induce considerable effects on the fresh and hardened properties of concrete. In this study, two types of cement (CEM I 52.5N and CEM III/A 42.5N) as well as crystalline admixtures and bacterial spores, both in powder form, and PCE-based superplasticizer are utilized to evaluate the changes in consistency and setting time. The dosage of healing agents is taken between 0 − 5% by weight of powders. To start, tests on paste level were executed. The results show that the addition of healing agents affects the water demand, the consistency and setting time of the pastes. The inclusion of crystalline admixtures increases the water demand, while a declined trend of setting time is observed. The gradual addition of bacteria up to 5% slightly changes the water demand, but a significant delay on the initial and final setting times was detected.

Harry Hermawan, Peter Minne, Enricomaria Gastaldo Brac, Virginie Wiktor, Pedro Serna Ros, Elke Gruyaert
Novel Compressive Constitutive Model for 3D Printed Concrete

3D concrete printing (3DCP) is emerging as a promising technology in the construction industry. From the engineering and architectural point of view, the use of 3DCP offers a great potential in terms of enhancing construction automation, more freedom of shapes and a substantial reduction of manufacturing costs associated with production and materials. Unlike traditional poured concrete, 3DCP is a layer-to-layer based manufacturing method. Such productive method makes concrete to present a layer-based structure than can lead to an anisotropic element because of the varying properties on the different spatial directions of the material. Consequently, and given the specific manufacturing method and the internal structure of 3DCP, a new approach in terms of constitutive models for design purposes is required. The objective of this is study is to develop a novel constitutive model for compression considering the influence of the anisotropy of the material. For this, an experimental program involving the characterization of 3D printed concrete specimens was conducted. The compressive strength and the modulus of elasticity was determined to obtain the stress-strain diagram on different loading directions, taking into account the influence of the layer-based structure of 3DPC. The results revealed no significant differences between spatial directions given the great homogeneity of the 3D printed concrete in all directions. However, such approach becomes necessary so engineers and designers can fully take advantage of the material and remain on the safe side of the structural design.

Eduardo Galeote, Albert de la Fuente
Effect of Nano-additives and Polymeric Viscosity Modifying Admixtures (VMA) on the Fresh and Hardened Properties of 3D Printable Concrete Mixtures

In spite of recent advances in construction digitization and concrete 3D printing, engineering a printable concrete mixture for extrudability and buildability still presents technical challenges. Nano-additives such as nano-silica and nano attapulgite clay are gaining increasing interest for their attributes as rheological modifiers. Recent studies showed some of the potential rheological benefits of these materials, although there is a lack of comprehensive studies in this domain. Polymeric additives, e.g. a cellulose derivative (Viscosity Modifying Admixture) and polycarboxylate ether (superplasticizer), can be combined with the nano-materials to enhance fresh properties. A comprehensive study is presented which depicted the effect of rheological modifiers on flowability and uniaxial compressive load resisting ability of fresh 3D printable concrete mixtures. A time-based flow table protocol was developed to document the change of flow diameter with time pertaining to the mixtures’ thixotropic behavior. Furthermore, the effect of uniaxial compressive loading on fresh concrete (“apparent green strength”) at different resting intervals from the time of mixing (i.e. at 30, 60, 90, and 120 min) was investigated. Fresh concrete specimens were subjected to compression and loaded until 40% vertical strain or complete failure, whichever occurred earlier. Based on the apparent stress-strain curves, the effect of resting time on the apparent stress, post-peak behavior and failure mode was analyzed.

Debadri Som, Cristina Zanotti

Structural Performance and Design

Shrinkage-Cracking Prevention in Large-Scale Concrete Structures by Means of Superabsorbent Polymers (SAPs)

SAPs have been widely studied over the past two decades as new admixtures for cementitious materials. Their ability to absorb and retain water from the cementitious mixture allowed them to be successfully used as internal curing agents preventing self-desiccation and reducing autogenous shrinkage. A lot of research has been developed and important advances have been achieved, but there is still a lack of studies reporting on the use of SAPs in large-scale structures. This paper presents results of a large-scale testing campaign in Belgium using a commercial SAP. Three reinforced concrete walls (dimensions 14 m × 2.75 m × 0.80 m) were built and monitored with regards to shrinkage and cracking. Two walls without SAPs and water-to-cement ratio of 0.44 and 0.52 were used as references. The SAP-wall was built with 0.38% (over the cement mass) of a commercial SAP, total water-to-cement ratio of 0.52 and effective water-to-cement ratio of 0.44. A laboratory campaign was performed simultaneously with the on-site one to fully characterize the concrete used in the walls. The addition of SAPs promoted a reduction of up to 75% of shrinkage strain in the first 7 days and up to 60% after 28 days. No cracks have developed in the SAP wall, while for the reference walls the first cracks were noticed 5 days after casting. The addition of SAPs caused a 17% reduction in compressive strength at 28 days compared to the reference with less water and 22% increase compared to the reference with more water.

José Roberto Tenório Filho, Didier Snoeck, Nele De Belie
Effect of Artificial Lightweight Aggregates on Interfacial Transition Zone in Concrete

Lightweight concrete has a history of more than two-thousand years and its technical development is still proceeding. Despite the diversity of lightweight aggregates available, some mechanical problems have limited their use as structural elements in the construction industry. In general, the mechanical properties of lightweight concretes are lower than normal weight concretes, being affected by factors such as the stiffness of the aggregate particles, the cement content and density. For this reason, significant efforts have been devoted to optimizing their dosage and improving their mechanical properties, to make them competent against conventional concretes. This tendency has led to the study of microstructure, particularly the mechanisms responsible for the interfacial transition zone (ITZ) formation, related with absorption and water release. This investigation focuses on analyze the characteristics of morphology of expanded clay and polymeric wastes lightweight aggregates and conclude that the impact of the ITZ on mechanical properties is of considerable significance, leading to modifying its mechanical behavior.

D. González-Betancur, Ary. A. Hoyos-Montilla, J. I. Tobón, B. Garcia
Durability Design and Quality Control/Assurance During Construction of Concrete Structures

The procedures performed for durability quality control/quality assurance (DQC/QA) of concrete during the construction of a bridge exposed to a tropical marine environment is presented. The methodology includes the use of one durability index to estimate the transport properties of aggressive agents in concrete, called saturated electrical resistivity (ρS). A second index commonly used internationally to determine the concrete’s typical QC/QA evaluating its compressive strength (fc) was also monitored. Both DQC/QA and QC/QA were made using standardized 10 × 20cm cylinders fabricated during the 2-year construction of the example bridge. The results obtained demonstrated that the DQC/QA for concrete should not be based solely on mechanical strength tests (fc), but also on physical tests that determine the ease (or difficulty) that the newly manufactured concrete could present to the transport of aggressive ions within. The statistical analysis performed showed that there was a greater variability in the results of some with ρS, using standardized cylinders, as compared to low variability obtained from fc QC/QA data obtained with same cylinders.

Andrés Antonio Torres-Acosta
Flexural Behavior of Reinforced Concrete Beams Made with Recycled Concrete Aggregates

The reuse of Construction and Demolition Waste (CDW) to produce new materials is an effective method for reducing the negative impacts from the inadequate waste disposition, in addition to bringing economic and environmental benefits to the industry. The use of Recycled Concrete Aggregate (RCA) in concrete is a technique widely disseminated, however, using this material for structural applications is a target of distrust among professionals in the construction sector. Therefore, the purpose of this study is to analyze the influence of using RCA to replace 100% of course natural coarse aggregates with size fraction 9.5–19 mm in the flexural behavior of reinforced normal-strength concrete beams (35 MPa). In addition to a reference mixture produced with only natural aggregates, a Recycled Aggregate Concrete (RAC) mixture was designed, according to the well-known Compressible Packing Model (CPM), using RCA from demolition waste. The mechanical behavior of the concrete mixtures was characterized by compressive and splitting tensile tests. A pair of flexural critical beams of each concrete mixture was tested under a supported four-point loading condition at the age of 28 days. All tested beams had 240 cm length and rectangular cross section of 20 × 30 cm2. The experimental cracking, yielding and ultimate load of the beams were measured. Besides that, the load-strain behavior for concrete was obtained, as well as the load-deflection behavior. The results showed that the flexural behavior of RAC beams was not negatively affected by the presence of RCAs.

Marianna S. Sodré, Maíra S. R. da Costa, Caroline S. Rangel, Mayara Amario, Marco Pepe, Enzo Martinelli, Romildo D. Toledo Filho
Analysis of Design Constitutive Model for Macro-synthetic Fibre Reinforced Concrete Through Inverse Analysis

The increasing use of fibre reinforced concrete (FRC) as a structural material requires a constant development of new tools for design purposes. In this line, different codes and guidelines include constitutive models for FRC in their specifications. However, these constitutive models are usually based on the behaviour of steel fibre reinforced concrete (SFRC) and present several limitations on representing the full behaviour of macro-synthetic fibre reinforced concrete (MSFRC). With the aim of analysing the suitability of the constitutive models when applied on macro-synthetic fibres, an experimental program to determine the performance of MSFRC using different fibre contents and concrete mixes was performed. The study of the constitutive models was conducted through an inverse analysis using a two-dimensional analytical model to verify and compare the FRC constitutive equations of the MC2010 with the experimental results. The constitutive model of MC2010 was selected given that it is able to capture both the softening and hardening behaviour of FRC through a three-point constitutive equation. The results show that the original constitutive model of the MC2010 tends to overestimate the performance of PFRC. Moreover, it could be necessary to include an additional point on the post-cracking branch of the constitutive model to represent more accurately the full residual strength of PFRC. The results also show that the ultimate strain of the constitutive model should be extended to fully capture the performance of PFRC, especially for large deformations. This study suggests that it should be necessary to redefine the constitutive models through a new approach distinguishing between FRC blended with steel or macro-synthetic fibres.

Eduardo Galeote, Alejandro Nogales, Albert de la Fuente
Mechanical Properties of Fiber Reinforced Concrete at Low Temperatures

The existing literature proves that the mechanical performance of fiber reinforced concrete (FRC) is sensitive to elevated temperatures, this being dependent on the type and amount of fibers. However, the majority of studies carried out thus far have focused on the assessment of the material behavior at elevated temperatures, disregarding the mechanical performance of FRCs at low temperatures. Taking this into account, an experimental program was carried out in order to evaluate the mechanical properties of FRC subjected to temperatures ranging from 20 ℃ to –30 ℃; the attention was directed to the post-cracking tensile strength, i.e. the property which is of paramount importance for FRC. Additionally, different concrete mixes were analyzed, varying both the type and content of fibers. The obtained results allow proving that the residual post-cracking tensile strength of the analyzed FRC mixes increased with the decrease of temperature in all presented cases. This positive outcome might serve as a reference (which should be complemented by further investigations) to properly design elements subjected to low temperatures during transient situations and/or service life.

Stanislav Aidarov, Nikola Tošić, Igor Reynvart, Albert de la Fuente
Finite Element Analysis Characterization of Macro Synthetic Fibre Reinforced Concrete Constitutive Equation

Over the last years, the use of fibre reinforced concrete (FRC) has increased for structural purposes. For the structural design of FRC elements, there was a need of a model that developed the behaviour of the post-cracking response of FRC. In this sense, national and international guidelines have included models to characterise the flexural behaviour of FRC (fib Model Code, EHE-08). These models gather the performance of FRC for serviceability limit state (SLS) and ultimate limit state (ULS) for either steel or macro synthetic polypropylene fibre reinforced concrete (SFRC and MSFRC, respectively). In this regard, the codes and guidelines do not distinguish between FRC comprised of steel or synthetic fibres and establish the FRC ultimate strain in 2.5%. This limitation represents the behaviour of SFRC but limits the full potential of MSFRC for large deformations. Owing to the aspects aforementioned, an extensive experimental programme has been carried out at the Universitat Politècnica de Catalunya (UPC) to characterise the behaviour of MSFRC. This research contribution is focused on an inverse analysis to derive the MSFRC constitutive equations by means of a non-linear finite element simulation. The main goal of this study is to compare the experimental results with those obtained through the simulation using the constitutive equations of the fib MC-2010. The results show a generalised underestimation of MSFRC at ultimate strain and the necessity of adjusting the constitutive equations for SFRC and MSFRC.

Alejandro Nogales, Eduardo Galeote, Albert de la Fuente
A Discussion on the Reliability of prEN1992-1-1:2021 Shear Strength Provisions for Fibre Reinforced Concrete Members Without Shear Reinforcement

The Eurocode 2 for the design of concrete structures (EN1992-1-1:2004) is undergoing a revision that will lead to the publication of the second generation of this code to be used across all CEN member countries. Therefore, the impact of the code will reach hundreds of millions of people. Importantly, the Eurocode 2-revision will incorporate many significant changes, amongst which is the introduction of design provisions for fibre reinforced concrete (FRC). In this regard, one of the most important aspects for ultimate limit state (ULS) design will be the consideration of the shear strength of FRC members without shear reinforcement. Such a failure mode is associated with a number of uncertainties, as well as with a potentially-brittle failure response. However, so far, the design models proposed in the Eurocode 2-revision have not been accompanied by a robust reliability-based calibration of the FRC partial factor γSF. Within this context, this paper presents the results of an investigation on the safety format and the partial factor γSF for FRC members without shear reinforcement currently provisioned in the draft for the new Eurocode 2 (prEN1992-1-1:2021). Firstly, a database of experimental results on FRC beams is used to determine the model error. On that basis, a probabilistic analysis is performed using the First Order Reliability Method (FORM) to determine adequate values of γSF for varying target reliability indices. The results of the study show how γSF values need to updated in order to reach reliability indices typically considered for ULS design.

Nikola Tošić, Jesús Miguel Bairán, Miguel Fernández Ruiz, Albert de la Fuente
Analytical Determination of Flexural Resistance of Rein-forced Concrete Beams with Corrosion

Corrosion of steel reinforcement is one of the main problems associated with deterioration of reinforced concrete structures. The dimensions of the cross-section of concrete and steel reinforcement is reduced due to corrosion. Because of this, structural strength of the concrete elements is also reduced. Therefore, the behavior of the structure can be committed. In this work, analytical and experimental strengths of reinforced concrete beams affected with corrosion are compared. The experimental strengths of 11 beams found in the literature were considered. The analytical flexural strength was determined by using the fundamental hypotheses of the flexural theory. The constitutive model of steel reinforcement was based on the model proposed by Rodríguez and Botero and the experimental results found in the literature. The relationship between analytical strength and experimental flexural strength varied between 0.97 and 1.12. Based on the results obtained, it was found that the strength of reinforced concrete beams affected with corrosion is predicted accurately using flexural theory. However, it is necessary to consider the reductions in the geometry of the beam, the reduction in the section in the longitudinal and transverse steel reinforcement; and corresponding changes in their constitutive models.

N. Vega, J. Moreno, P. Castro Borges, J. Varela
Analysis of Shear Panel Elements Using Improved Fixed Strut Angle Model Based on Plane-Stress Element

The behaviour of reinforced concrete (RC) member can be evaluated by employing a reasonably accurate constitutive relationship and element type in the finite element (FE) framework. Important components like columns, beams and shear wall in an RC structure can be analysed in the FE framework by using a plane-stress element. In general, RC members are subjected to the combination of axial, shear, flexure, and torsional loading. Hence, it is necessary to use constitutive models which can consider the effects of combined loading. This work focuses on implementing an improved fixed strut angle model in finite element framework to analyse shear panels under combined shear and axial loads. The proposed procedure is based on secant stiffness based iterative formulations and employs constitutive relationships which consider the concrete softening and tension stiffening. The material models and the equilibrium conditions based on the fixed strut angle model were implemented into MATLAB based FE framework. The reliability of the proposed analytical model is checked against the experimental results available in the literature. Moreover, it is essential to use efficient material constitutive relationships which can be effectively implemented in a finite element framework without compromising the accuracy of the predictions. A comprehensive analytical study is carried, wherein predictions were obtained using different combinations of material models. Comparison of the results shows that the predictions of the proposed model agree well with the test results.

Nikesh Thammishetti, Shanmugam Suriya Prakash, Trevor D. Hrynyk, Javad Hashemi, Riadh Al-Mahaidi

Non-Portland Cements and Alkali-Activated Cementitious Materials and Eco-concrete

Feasibility Study of One-Part Alkali Activated Material with MSWI Fly Ash

With the growing population, it is also expected that the municipal solid waste (MSW) generation would be increasing in the coming years. Management of MSW is already an identified issue and the incineration process is widely adopted as a disposal solution for non-compostable wastes. Incineration of MSW results in secondary waste residues such as almost 20% of fly ash and 80% of bottom ash. These are rich in silica and alumina content, naturally has the potential to be an aluminosilicate precursor to produce alkali-activated materials. Several issues are pointed out for the application of MSWI residues as cementing materials, either a Supplementary Cement Material (SCM) or an Alkali-Activated Material (AAM). One such issue concerning AAM application is the presence of metallic aluminium. Heavy metals from the MSWI residues are normally extracted before disposal, however metallic aluminium is not effectively removed in most of the cases. Metallic aluminium acts as a pore-forming agent by generating H2 gas in the alkali environment, thereby reducing the strength properties. In the present study, an attempt is made to understand the influence of the metallic aluminium present in the MSWI fly ash of different size fractions, fine (0–0.5 mm) and coarse (0.5–1.0 mm). MSWI fly ash is activated with solid/liquid alkalis, such as sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and combination of both. With the Na2O content maintained constant across the activators, the sample activated with NaOH is the weakest and the one with sodium silicate is the strongest with small, well-distributed pore structure, irrespective of the size fraction of MSWI fly ash used. Solid activator performed equally well as that of the liquid one.

Priyadharshini Perumal, Mirja Illikainen
Effect of the Limestone Content on the Durability of Alkali-Activated Limestone-Metakaolin Subjected to Acidic and Sulfate Environments

New alkali-activated cements based on calcined kaolinitic clays and limestone are a promising sustainable alternative to portland cement due to their improved mechanical properties and reduced environmental impact. Studies on durability are needed in order to gain knowledge for the scientific community and buy-in from potential stakeholders. In this investigation, alkali-activated limestone-metakaolin pastes were formulated with 20 and 60% limestone, activated with sodium silicate solutions, cured for 28 days and subjected to chemical attack by solutions of (a) 0.1 N HCl and (b) 5% MgSO4 for 7, 28 and 90 days. Changes in strength, mass, microstructure and reaction products were studied. The samples exposed to HCl underwent a degradation of the external microstructure due to a dissolution of calcium carbonate and depolymerization of the N-A-S-H/N-(C)-A-S-H gel, which led to porosity, cracks and loss of weight. After the exposure to MgSO4, all samples underwent a mass increase and the formation of quintinite was detected; formulation with Na2O/Al2O3 = 1.08 underwent microcracking. Despite de microstructural and mass changes, samples with low Na2O/Al2O3 of 0.60 preserved their strength after the period studied in both environments, regardless of the limestone content. This considerable chemical durability against acid and sulfate attack could extend the applications of alkali-activated limestone-metakaolin cements making them part of the future toolkit of durable binder technologies.

Pedro Perez-Cortes, J. Ivan Escalante-Garcia
Water Transport Properties of Hybrid Binder Concrete Containing Activated Copper Slag and Recycled Concrete Aggregate

Advanced design of eco-friendly concrete is very urgent in view of the vital fight against climate change. An interesting eco-efficient strategy is the combination of (1) alternative low carbon hybrid binders with a low clinker factor and the inclusion of alkali activators, (2) substituting natural aggregate by recycled aggregate and (3) securing satisfactory durability performance. Transport properties of concrete are reliable indexes concerning the ingress rate of aggressive agents though the pore structure. The present study analyses the water transport properties of concrete made with hybrid binders and recycled concrete aggregate. Copper slag (70 wt% binder) and copper slag + ground granulated blast-furnace slag (GGBFS) (50 and 20 wt% binder, respectively) were used as precursors with a tailored activator based on sodium sulfate and Portland cement. Coarse recycled aggregate (category Rcu 90 according to EN 12620) was used as 50% of total content of coarse aggregate (particle size range 4/32 mm). The examined properties include capillary absorption rate, water penetration under pressure, and accessible porosity by vacuum saturation at curing ages of 28 and 90 days. Concrete performance was dominated by the type of binder, whereas the impact of the recycled aggregate on the transport properties was in second place. A limited content of GGBFS in the binder system proved efficient to improve concrete performance. Overall, these preliminary results reflect promising capabilities of the combined strategy of using low carbon hybrid binders and recycled aggregates in concrete.

Yury Villagrán-Zaccardi, Pithchai Sivakumar, Nele De Belie
Early Age Properties of Paste and Mortar Made with Hybrid Binders Based on Portland Cement, GGBFS and Sodium Sulfate

Nowadays, Ground Granulated Blast-Furnace Slag (GGBFS) is increasingly used together with Portland cement to design low carbon footprint binder systems. Such systems with a low clinker factor are generally connected with a slow strength development. Alkaline activation in hybrid binders can provide a suitable solution to cope with this issue. Among the possible activators, sodium sulfate offers the advantage of its low-carbon footprint and good performance in the presence of Portland cement; however, in addition to strength development, other early age properties are also affected and compliance with requirements in the field must be verified. In the present study, hybrid systems based on Portland cement, GGBFS and sodium sulfate were analysed. Sodium sulfate was used in doses between 0 and 10 wt% relative to GGBFS. The GGBFS content amounted to 70 wt% of the binder and water-to-binder ratio was 0.45. Accelerated setting was detected due to the addition of sodium sulfate using the Vicat test and ultrasonic pulse velocity analysis. Increases in early age strength were observed for all the analysed doses of activator. Such increases are attributed to a dual effect: the acceleration of cement hydration and the enhanced dissolution of the slag. On this basis, possible changes in the reaction mechanism in presence of sodium sulfate have been discussed. Upon a comprehensive analysis of results, an optimal content of 5–10% of sodium sulfate in the mixes is suggested.

J. M. Etcheverry, P. Van den Heede, Y. A. Villagran-Zaccardi, N. De Belie
Review and Experimental Investigation of Retarder for Alkali-Activated Cement

Alkali-activated cement (AAC) cured at ambient temperature conditions have a wider application area compared to heat cured AAC. High calcium precursor materials such as ground granulated blast furnace slag (GGBS) are commonly used to achieve ambient curing behavior. However, the GGBS results in a short setting time. Hence setting adjustment is critical in such AAC systems. This paper reviews state-of-the-art in the area of retarders for AAC systems. The most promising prospective retarders such as zinc salts, borax, sucrose, and phosphates are investigated. The retarder’s effect is dependent on the precursor materials and alkaline activators used. Consequently, in the review, these are identified for each retarder discussed. Some of the retarders were then tested in AAC with a blended precursor system containing fly ash (FA) and GGBS activated with sodium hydroxide and sodium silicate. The results showed that each borax percentage, with respect to the total solid binder, increases the setting time by about 50% of the mix without borax. Sucrose, sodium acetate, acetic, and phosphoric acids have no significant effect on the investigated AAC’s setting time.

Klaus Holschemacher, Biruk Hailu Tekle
Sustainable Cements: Hybrid Alkaline Cements Overview

The ordinary Portland cement (PC) production contributes 2–3% of global energy use and 8% to 10% of world-wide carbon dioxide emissions (CO2). According to estimates in 2050, the CO2 emissions associated with the manufacture of PC, could increase between 240–260% compared to the 1990 emissions. Faced with this need, the Portland cement industry has been considering several options. One of them is to replace Portland clinker to the greatest extent possible, with low-carbon Supplementary Cementitious Materials (SCMs) (whether added with the cement or directly into the concrete mix, “Blended cement‟). The type and quantity of mineral additions is regulated by the standards of each country, although these values do not usually exceed 35%. Higher values are not allowed because the early mechanical strength decreases. However, applying alkaline activation technology can reach replacement levels of up to 60% or 70%, in the so-called “Hybrid Alkaline Cements” (HAC). The SCMs are basically natural pozzolans, such as blast furnace slag (BFS) or fly ash (FA). To increase the reactivity of mineral additions, especially at early ages, an alkaline activator is added into the mixture, normally salts of moderate alkalinity. This work shows a review of the theoretical knowledge of the hydration of hybrid cements, as well as their mechanical performance in mortars, concrete, and in industrial-scale applications.

A. Fernández-Jiménez, I. Garcia-Lodeiro, O. Maltseva, A. Palomo
One Part Blast-Furnace Slag Cements Activated with a Blend of MgO-Na2SO4

In order to reduce the use of sodium silicate solutions and hydroxides for the alkaline activation of materials, the combination of alkaline activators has a positive effect to produce alternative cements with environmental advantages in relation to Portland cement-based materials. This research report results of compressive strength and reaction products of blast-furnace slag cements activated with a mixture of MgO-Na2SO4 with a ratio 1:1 added in 4, 6 and 8% relative to the slag weight. Pastes of alkali activated slag were prepared and cured at 20 ℃ and 60 ℃-24h-20 ℃ up to 90 days. Samples at 20 ℃ did not show a strength gain during the first 3 days of curing, but after 7 days the strength increased noticeably of up 53 MPa at 90 days. It also was observed that curing at 60 ℃ favored a gain of compressive strength at early ages between 20-30MPa with a marginal increase at 90 days. The use of the mix MgO-Na2SO4 was favorable for the chemical activation of the slag without detrimental effects on the stability of the formulated samples. The microstructures consisted of C-S-H, ettringite, hydrotalcite and some traces of CaCO3 from the raw material.

I. E. Betancourt-Castillo, J. A. Díaz-Guillén, J. I. Escalante-García, O. Burciaga-Díaz
Blended Limestone-Portland Cement Binders with Low Amounts of 2 Powdered Sodium Silicates

The effect of the addition of 2 sodium silicates of modulus = 3.2, one commercial powdered sodium silicate (CSS) and one prepared on the base of waste glass-based (WGSS), was evaluated on limestone-Portland cement binders. An experimental design of three components mixture was used to formulate mortars with water/binder = 0.46, 2–20 wt.% CSS and 10–70% of Portland cement (PC); while for WGSS was used in a mortar with 40%PC, water/binder = 0.25. The aggregate/binder was kept at 2.75. The silicates were compared among similar mortar formulations in terms of compressive strength, flowability, microstructure and CO2 emissions. The CSS had a positive effect on the strength of mortars made with binders with 10 and 40%PC, but not in those with 70%PC. The flowability of all mortars was of about 130 mm and the use of low amounts of alkaline sodium silicates did not affect the performance of the superplasticizer (added at 0.05% wt. Relative to the mass of the binder). The performance of mortars prepared with WGSS was better than those with CSS; the former reached 40 MPa at 28 days, which was similar to reference 100%CP mortar. The irregular particles of WGSS had a better interaction with the cementitious matrix compared to the spherical particles of the CSS. On the other hand, emissions of the mortar with WGSS was 30% and 40% lower than mortars with CSS and the reference with PC, respectively. Overall, the use of the WGSS in mortars with low water/binder and 40%PC showed similar performance and lower environmental impact compared to the use of 100%PC mortars.

José Luis Santana-Carrillo, Oswaldo Burciaga-Díaz, J. Iván Escalante-García
Hydraulic Pastes of Alkali-Activated Waste Glass and Limestone Cement Using in Situ Caustification

One-part waste glass (WG) and limestone (LS) alkali-activated cements were investigated in pastes using powdered activators CaO+Na2CO3. 9 formulations of pastes were selected from a full factorial experimental design with %LS, %Na2O-Na2CO3 and %CaO as factors. The activators promoted an in situ caustification that dissolved the WG amorphous structure leading to the formation of cementitious reaction products. The pastes developed 1-year strengths up to 35 MPa and were stable underwater. The characterization by SEM, EDS and 29Si-NMR indicated that while using a Na2CO3:CaO ratio close to 1:1, the main reaction products were polymerized C-S-H, silica gel and modified silica gel, intimately intermixed and crosslinked through Q3 bonds. Such coexistence of reaction products was better in terms of strength and underwater stability than those coexisting in pastes of WG+LS systems activated with solutions of only NaOH reported in literature. Moreover, curing underwater promoted the formation of shorter silicon-oxygen chains, suggesting more formation of C-S-H; nonetheless, the considerable presence of Q3 and Q4 signals along with a 1-year compressive strength of 32 MPa in pastes cured underwater evidenced that most of the silica gel was stable. The results indicated that in situ caustification is a promising one-part activation for SiO2-rich precursors such as waste glass to develop hydraulic alkali activated cements with low cost and CO2 emissions.

L. E. Menchaca-Ballinas, J. I. Escalante-García
RILEM TC 281-CCC Working Group 6: Carbonation of Alkali Activated Concrete—Preliminary Results of a Literature Survey and Data Analysis

The current understanding of the carbonation of alkali-activated concretes is hampered inter alia by the wide range of binder chemistries used. To overcome some of the limitations of individual studies and to identify general correlations between their mix design parameters and carbonation resistance, the RILEM TC 281-CCC working group 6 compiled 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. A preliminary analysis of the database indicates that w/CaO ratio and w/b ratio exert an influence on the carbonation resistance of alkali-activated concretes but, contrary to what has been reported for concretes based on (blended) Portland cements, these are not good indicators of their carbonation resistance when considered individually. A better indicator of the carbonation resistance of alkali-activated concretes under conditions approximating natural carbonation appears to be their w/(CaO + Na2O + K2O) ratio. Furthermore, the analysis points to significant shortcomings of tests at elevated CO2 concentrations for low-Ca alkali-activated concretes, indicating that even at a concentration of 1% CO2, the outcomes may lead to inaccurate predictions of the carbonation coefficient under natural exposure conditions.

Gregor J. G. Gluth, Xinyuan Ke, Anya Vollpracht, Susan A. Bernal, Özlem Cizer, Martin Cyr, Katja Dombrowski-Daube, Dan Geddes, Cyrill Grengg, Cassandre Le Galliard, Marija Nedeljkovic, John L. Provis, Zhenguo Shi, Luca Valentini, Brant Walkley
Alkali Binder Based on Waste Glass and Limestone

Investigation was carried out about to characterize the reaction products and strength of pastes of alkaline binders based on urban waste glass and limestone activated at 20, 40 and 60 ℃ with 6, 9 and 12% Na2O using NaOH, Na2CO3 and a mixture of these. The waste glass and limestone were ground to pass through the #50 (150µm) and #325 (45µm) sieves. The investigation was developed in two stages. First, the Taguchi Method, which is a fractional experimental design, was used to determine the conditions that promote the greatest compression strength. Second, pastes were prepared using a factorial experimental design to be able to evaluate and compare the effect of activators on compressive strength and microstructure. The results showed that the use of Na2CO3 promotes the highest compressive strength (71 MPa), but the structural stability decreases after 14 days of curing at temperatures greater than 40 ℃. The use of the Na2CO3/NaOH mixture was considered optimal, according to Taguchi statistical method, the compressive strength at 28 days of curing was of 64.8 MPa ± 15 MPa, maintaining structural stability in late curing ages. The pastes prepared with NaOH developed the least strength at early ages, but in later stages it can promote compressive strength similar or greater than those developed by the pastes prepared with the other activators used (59 MPa, 28 days). The characterization carried out by XRD, SEM and TGA-DSC indicates that the reaction products formed were pirssonite, gaylussite, recrystallized calcium carbonate and C-S-H intimately intermingle with silica gel.

U. Avila-López, J. I. Escalante-García

Cultural Heritage

Materials Characterization and Compressive Strength of Compressed Earth Blocks Reinforced with Oat Straw

This paper describes the material characterization, compressive strength, and chemical composition of two compressed earth blocks (CEBs) stabilized with oat straw. The properties of the oat straw and soils used for the improvement of the CEBs were evaluated. The compressive strength was assessed by randomly choosing and testing 26 pieces. In addition, the chemical composition was obtained. As a result, the unit density of the oat straw is within the top limit of the experimental referenced values; however, the absorption records the highest value, i.e., one outside of the experimental referenced range. The soil properties are within the ranges defined by international standards. The compressive strength is adequate for both pieces (2.9 MPa for CEB A and 4.7 MPa for CEB B), but the initial absorption is high. Silica and calcium oxide comprise 90% of the chemical composition of the two pieces. Considering the high absorption of these CEBs, their colocation is not recommendable in the lower parts of walls. This is to avoid standing water in the foundation soil. The highest compressive strength of CEB B is related to the plastic index and chemical composition.

Sulpicio Sánchez Tizapa, Gerardo Altamirano de la Cruz, Alfredo Cuevas Sandoval, Adelfo Morales Lozano, Ángel Moreno Dimas, Luis Alberto Patiño
How Different is the Deteriorating Mechanism of Fired Clay Bricks Due to NaCl Salt Compared to the Highly Damaging Na2SO4?

Deterioration due to salt crystallization or physical salt attack is one of the crucial issues faced by the world’s architectural heritage. Sodium sulphate is known for its highly damaging nature and hence adopted universally as the deteriorating agent by various laboratory salt degradation tests. There exists a general disagreement in the research community regarding the damaging nature of NaCl to masonry structures, perhaps due to a lack of sufficient information regarding the mechanism of decay. The current paper analyses the degree of deterioration and mechanisms in various brick types in the presence of NaCl and compares that with the mechanism of Na2SO4 damages. Accelerated salt weathering tests were conducted as per the RILEM V 1.b test procedure followed by the micro-analytical characterization of samples post-degradation. The difficulty in attaining higher supersaturations was observed in the case of NaCl, which resulted in a much slower rate of degradation. The role of microstructure of the material in altering the damage mechanism is elucidated using data collected with Mercury Intrusion Porosimetry and Scanning Electron Microscopy. Also, a question on choosing the right protective treatment for the samples on various exposures- sodium sulphate and sodium chloride is addressed.

Swathy Manohar, Manu Santhanam
Effect of Soil Characteristics on the Physico-mechanical Properties of Non-stabilized Compressed Earth Blocks

In an attempt to investigate the effect of soil characteristics on the physico-mechanical behavior of non-stabilized Compressed Earth Blocks (CEBs) produced in Cyprus, four types of locally sourced soils, with different mineralogical/granular composition and plasticity characteristics, have been examined and used for CEB production. A series of tests, including particle-size analysis, Atterberg limits determination, shrinkage and compaction measurements, and X-ray diffraction (XRD) analyses have been carried out to determine the characteristics of the raw materials selected. In addition, compression and three-point bending tests, capillary absorption measurements, thermal conductivity analyses, and scanning electron microscopy (SEM) analyses have been conducted to assess the physico-mechanical properties of the CEBs produced. The results indicate that, despite the different granular composition of the soils used, all CEBs produced demonstrate adequate mechanical properties in terms of compressive (over 5 MPa) and flexural (over 0.5 MPa) strength. The X-ray diffraction (XRD) analyses confirm that the soils investigated are mainly composed of carbonates and silicates at different ratios, in line with their geological origin. The thermal conductivity of all specimens tested ranges between 0.60–0.85 W/mK, while capillary absorption measurements have shown higher sorptivity in the specimens with extended micro-cracks and voids.

M. A. Kyriakides, R. Panagiotou, R. Illampas, I. Ioannou
Salt Deterioration of Heritage Structures—Correlating the Insights from Field and Lab Studies

Salt deterioration is unequivocally reported as the most crucial cause of the degeneration of coastal heritage structures. However, the deterioration patterns differ greatly for various sources and conditions, which are difficult to simulate exactly in laboratories. There are mixed effects and mechanisms of various salts getting crystallized in the same structure depending upon the differences in the microclimate. Insights developing from laboratory studies, even though they cannot replicate similar weathering, can be suggestive of the decay variations observed in the field conditions. In the current study, brick samples of the same origin but distinctive damage patterns collected from a heritage fort near the seashore were analyzed for physical and microanalytical properties. Combined and separate effects of sodium chloride and sodium sulphate were observed in the historic bricks and were then simulated in studies on fresh bricks in the laboratory. The extent and nature of damage in the field and lab samples were assessed with the help of characterization techniques such as XRD, SEM and MIP. Phase transitions of sodium sulphate were analyzed in the accelerated weathering studies conducted in the lab and correlated with the varying exposure conditions of the field. The study contributed to providing a clear understanding of the different decay mechanisms and damage patterns observed at the site in relation to the standard salt deterioration tests conducted in labs.

Swathy Manohar, V. A. Anupama, Manu Santhanam
Durability of Heritage Masonry Structures: Review on the Substrate-Mortar Interaction

Much of the built heritage stock comprises masonry units of stone or brick, adhered by lime mortar. The properties of the materials used in the construction play a pivotal role in the strength and long-term durability of the masonry structures. The breathability of lime mortar, the porosity of substrates, and the properties of the substrate-mortar interface are critical to the extended serviceability of the structure. The current study focuses on a review of the substrate-mortar interface properties developed over short-term and long-term durations. The fundamental mechanisms of adherence and material transport across the interface were studied in detail. Analysis of physico-hygro-thermal influences on masonry structures was found to give crucial insights on the porosity and pore size distribution of the unit, mortar and the interface. The mortar properties such as water content and composition were found to have a significant impact on the bond strength development. The microstructural investigations using characterization techniques confirmed that the network of products formed at the interface by hydration and carbonation also governed the interface porosity. The study on the weathering characteristics that modify the transport parameters is critical for understanding the fundamental principles behind moisture attack and salt crystallization in ancient structures, typically on coastal monuments. The study provided a comprehensive insight into the transport mechanisms and the critical parameters for consideration during the design of mortars for restoration.

V. A. Anupama, Manu Santhanam
Mexico’s Caminos Reales (Royal Roads) Bridges: Location Based on Georeferencing Techniques

After the establishment of the Viceroyalty of New Spain in the 16th century, interest in precious metals and mining influenced the emerging economic activities and the communications network of New Spain. All communication infrastructures were built along two mutually perpendicular axes. The first axis ran east to west (connecting Veracruz–Mexico City–Acapulco), and the other axis ran north to south (linking the northern part of the Viceroyalty with New Mexico-Zacatecas-Mexico City–Oaxaca–Guatemala). As part of the road infrastructures needed to get a continuous flow of goods, bridges were very important for crossing rivers, cliffs, and mountains. Fabrication of these structural elements was based mainly on Roman old-school methods. The geometry, length, and materials used were varied, depending on local labor expertise and the technical improvements at the time. Vestiges of viceregal bridges are scattered across the 2 million km2 of present-day Mexico. Most of them are still in use, but other old Royal Roads were forgotten when they went out of use. This investigation deals with the use of methodology based on information technology to create a web-based management system for viceregal bridges, which is now available for use by the three levels of government in Mexico (Municipality, State, and Federal) and by research institutions.

Andrés A. Torres-Acosta, Joel Bustamante-Altamirano
Towards Green Materials for Cultural Heritage Conservation: Sustainability Evaluation of Products for Stone Consolidation

Formulation of effective stone consolidants for the restoration of weathered carbonate substrates is an active area of research in conservation science. In addition to consolidation performance, sustainability is increasingly taken into account in the selection of the most suitable conservation intervention. Here, a comparative life cycle assessment of three consolidants (a novel product based on a diammonium hydrogen phosphate solution and two commercial alternatives: nanolimes and acrylic resin) was carried out to determine the environmental burdens that might arise from their production, their application processes, and the supply chain of precursors and auxiliary materials. The impacts of the three consolidants were compared considering the respective amounts required to treat 1 m2 of two alternative substrates (limestone and lime mortar), as determined by application until apparent refusal. The results of the study highlight the lower environmental footprint of the phosphate-based treatment compared to the commercial solutions on several impact categories. The analysis allows to point out, for each product, the components that contribute the most to the environmental impact, namely solvents in the case of the commercial consolidants and production of DAP itself in the case of the phosphate treatment.

Alessandro Dal Pozzo, Giulia Masi, Alessandro Tugnoli, Enrico Sassoni
Limestone Consolidation: How Much Product is Enough?

This study was aimed at evaluating the performance of four different consolidants (ammonium phosphate, nanolimes, ethyl silicate, acrylic resin) when applied onto a porous limestone (Lecce stone) by different number of brush strokes, with the aim of identifying the optimal product consumption for each consolidant. The results of the study indicate that, in the case of nanolimes and acrylic resin, insufficient mechanical consolidation and resistance to accelerated ageing is achieved even increasing the number of applications, likely because of a scarce penetration depth. In the case of ethyl silicate, increasing the product consumption leads to increasing mechanical effectiveness, which however is linked to significant color change and alteration in water absorption, as well as scarce resistance to freezing-thawing cycles. Ammonium phosphate was able to induce significant consolidation even for the lowest product consumption. By increasing the number of brush strokes, an increase in mechanical effectiveness was registered. For the highest number of applications, the mechanical improvement caused by ammonium phosphate was slightly lower than that caused by ethyl silicate, but ammonium phosphate had the important advantage of not causing any compatibility issue and resisting to freezing-thawing cycles better than all the other alternative consolidants.

Giulia Masi, Enrico Sassoni
Effects of Steam-Slaking on the Characteristics of Lime from Three Different UK Manufacturers

The practice of producing lime mortars by slaking the quicklime directly in the sand rather than water is known as hot-mixing and, according to numerous historic accounts, was much more common in the past centuries than is generally appreciated by the majority of practitioners. During the last decade, a renewed interest has been dedicated toward the study of the hot-mixed mortar technology, as these mortars are regarded by most craftsmen of superior quality with respect to putty-based mortars in terms of workability, durability and other physical and mechanical properties. In such systems, the slaking of the quicklime is carried out by the moisture surrounding the sand grains and a small amount of added water. The steam developed by such initial slaking promotes further slaking which is supposed to be crucial in determining the characteristics of the lime, and, consequently, of the mortars. However, there are very few in-depth investigations regarding the role of steam on the characteristics of slaked lime. In this study, we have investigated the effects of steam slaking on the characteristics of lime produced by slaking the quicklime from three different UK manufacturers: Lhoist UK, Singleton Birch and Tarmac. Microstructural and mineralogical characteristics of the steam slaked limes are compared with those of the same limes slaked in excess of water and of the related oxides. Analyses were performed using X-ray fluorescence, scanning electron microscopy, and crystallite size and platelet abundance measured by X-ray diffraction data. The results provide useful information on the relations between the characteristics of the limestone used to produce the oxides and the effects of different slaking methods on the characteristics of the slaked lime. This can aid professional conservators to choose the right material and slaking method for the production of compatible mortars in conservation works.

Cecilia Pesce, Martha C. Godina, Alison Henry, Giovanni L. Pesce
A New Research Strategy in Studying and Improving the Bond Between Concrete and Repair Mortar

The required depth of concrete removal should dictate the selection of concrete removal technique and removal energy in repair systems. This study presents a new research approach in the investigation of the impact of concrete removal techniques on the substrate, and as a result, the bond with repair mortar. On the other hand, it introduces a remedy to improve the bond strength. To this end, crushed limestone concrete (CC) was made and the substrate surface was removed until a certain depth (2–3 cm) by using two commonly used techniques: jack-hammering (7 kg), and hydrodemolition/water-jetting (100 MPa). The selection of removal technique and energy was according to the defined removal depth. Automated laser measurements (ALM) were employed to study the surface roughness of the substrates. Later, the bond strength results of jackhammered-CC samples were compared with those of another study, for which the same removal depth was applied to a gravel concrete (GC) substrate by using a lighter jackhammer (1.5 kg). Moreover, nano-silica was used to improve the bond strength of jack-hammer treated substrates with the repair mortar.

Mohammad Ali Yazdi, Elke Gruyaert, Kim Van Tittelboom, Nele De Belie
Ammonium Phosphate for “Green” Conservation of Cultural Heritage: 10 Years of Research in the Laboratory and in the Field

This paper presents a summary of results obtained in the last 10 years on the use of ammonium phosphate solutions for conservation of heritage stones and mortars. After a brief introduction about the genesis of this treatment, the most used formulations are presented. Various functionalities of the treatment are reviewed, then its compatibility and durability are discussed. Recent results on the treatment environmental sustainability are also reported. The treatment’s performance in comparison with alternative consolidants (ethyl silicate, nanolimes, acrylic resin) is then evaluated and, finally, some pilot applications of ammonium phosphate onto real buildings and monuments are reviewed. All the laboratory and field studies published so far point out ammonium phosphate as one of the most promising inorganic treatments currently available for conservation of heritage materials.

Enrico Sassoni
Characterization and Physical-Mechanical Properties of Adobes from La Huacana, Mexico

Earthen architecture is one of the oldest construction solutions known, with archaeological evidences as ancient as the first human settlements. Nevertheless, in the last decades, adobe constructions have been abandoned and severely modified, been displaced by the use of industrial materials like concrete blocks and ceramic bricks. The importance of these traditional systems in the local communities is a crucial aspect, since the techniques have been transmitted for generations and are part of the inner culture. Adobe samples from heritage buildings, including complete specimens and cylinders, were collected in the town of La Huacana, in the state of Michoacan, in Mexico. Also these structures were surveyed and analyzed from the technological and architectural study of the buildings and materials. After the field work the samples were brought to the materials laboratory of the Michoacan University of Saint Nicholas of Hidalgo and were analyzed with non-destructive tests, mechanical resistance and soil mechanics trials. The experimentation allowed to calculate the mechanical resistance as well as the ultrasonic pulse velocity; the results were compared to the sieve analysis, the Atterberg limits and the USCS (Unified Soil Classification System) of the samples. The material characterization of the adobes allowed to determine the properties of these construction materials, which commonly are not deeply studied. The samples from La Huacana presented a very singular composition with great percentages of fine material, while the mechanical properties were quite satisfactory in comparison with the background researches. It is expected to perfect and regulate the characterization of earthen materials by means of research works like the one presented, achieving a complete perspective of these traditional systems.

Adria Sanchez-Calvillo, Elia M. Alonso-Guzman, Wilfrido Martinez-Molina, Hugo L. Chavez-Garcia, Melissa Ruiz-Mendoza
Conservation of Cultural Heritage Building: Evaluation of Ca[Zn(OH)3]2·2H2O Nanoparticles Coating Behavior Under Salt Crystallization Cycles

Calcareous stones are composed of a mixture of minerals and different cementing agents. Due to their heterogeneity, they are sensitive to the action of multiple environmental factors, including temperature, relative humidity, solar radiation, microorganisms, and salt crystallization processes that are the cause of degradation, inducing changes in their physical and chemical properties. Then it is desirable to account for specific studies on new nanomaterials that improve stone characteristics to extend its performance for long periods. In Yucatán, the calcareous stone is a traditional building material used since the prehispanic period, however, its susceptibility to deterioration has created a demand to elaborate protective treatments that improves its consolidation. This work shows the performance of new nanomaterials synthesized via sol-gel, based on calcium and zinc hydroxide dihydrate, with the formula Ca[Zn(OH)3]2·2H2O (CZ) and applied on three Yucatán calcareous stones Calcehtok, Chichén Itzá and, Mayapán, and further evaluated under the sodium sulphate crystallization aging test. Results indicated that after applying CZ nanoparticles (NPs) to stones, physical and mechanical properties like capillarity, colour, propagation of ultrasonic velocity, and structure improved as they showed a decrease in stone cracks, cavities, and pores. The salt crystallization tests indicate significant changes in the control properties of untreated stones when compared to those specimens coated with CZ. In addition, a better performance was observed for the stones from Calcehtok, followed by Mayapán and Chichén Itzá, respectively.

Montserrat Soria-Castro, José Faisal-Sulub, Katia Josceline Pérez-Ostos, Aketzali Abigail García-Reyes, Javier Reyes-Trujeque, Patricia Quintana-Owen, Susana del Carmen De la Rosa-García, Claudia Araceli García-Solís, Sergio Alberto Gómez-Cornelio
New Sensors for Moisture Monitoring in Historic Walls: Preliminary Results

The presence of moisture in historic masonry walls represents one of the main sources of decay for cultural heritage and materials, besides causing unhealthy indoor conditions and worsening the thermal performance of the building envelope. In fact, moisture causes and/or exacerbates different deterioration mechanisms, such as salt crystallization, freeze-thaw cycles, biological growth, etc. Given the importance of moisture in materials, there are many techniques aimed at determining moisture content in structures, but the most common ones only provide qualitative results or do not allow reliable repeated measurements over time, which is a severe limitation when continuous monitoring is necessary. In this perspective, the MIMESIS project (funded by Emilia-Romagna Region, Italy) aims at developing a range of sensorized materials for the remote monitoring of moisture, temperature, pH and detachment, useful to determine the ‘health state’ of historic buildings. It is also expected that the sensorized materials give a warning when critical situations are reached, allowing to carry out adequate interventions before irreversible damage occurs. In this paper, a brick-based sensor suitable for measuring moisture content in masonry was developed and tested. The sensing element was originally designed for agriculture, to measure the ‘soil water tension’, hence an investigation about the applicability to building materials and a calibration in bricks was necessary. The results are encouraging and suggest that this new sensorized brick could be applied for the continuous monitoring of moisture in historic masonry.

Mattia Bassi, Elisa Franzoni

Non-Destructive Testing Techniques

Fresh Concrete Curing Monitoring Using Acoustic Emission

In the present paper, acoustic emission (AE) is applied to monitor internal curing of fresh concrete. Processes taking place during the fresh state of concrete prove to be very acoustically active allowing detailed monitoring of the events. These processes include, settlement, production of hydrates, shrinkage cracking and correlate well with other measured parameters like ultrasonic pulse velocity and compressive strength. It is also characteristic that internal curing owing to the addition of superabsorbent polymers (SAPs) contributes to large numbers of AE activities, exhibiting the potential of the technique to distinguish between different sources based only on passive and non-intrusive use of sensors on the external side of the mold. The heavily damping nature of fresh concrete necessitates elaborate design of the setup and optimization of the sensors’ placement. Parameters like the total AE activity, amplitude, average frequency and time domain characteristics prove very useful in characterizing the process of internal curing. The possibility to control the curing based on the results of acoustic monitoring is also discussed.

Ashwin P. S. Dias, Gerlinde Lefever, Dimitrios G. Aggelis
Crack Closure Assessment in Cementitious Mixtures Based on Ultrasound Measurements

Cracking of cementitious materials poses severe problems for the mechanical performance and the durability of concrete structures. Self-healing cementitious materials provide a means of countering these issues, but the testing procedures to assess the self-healing efficiency are mostly impractical for in-situ evaluation. This study concerns the evaluation of the crack closure in cementitious mixtures with and without superabsorbent polymers by ultrasound measurements. Ultrasonic waves are sent through the cracks by means of pencil lead break tests, thereby offering information on the sound material as well as on the healing products formed within the cracks. The healing process is promoted by placing the specimens in wet-dry curing cycles and is monitored for a period of 14 days. Ultrasound was found to be sensitive to the closure of cracks, which was confirmed by the visual reduction in crack width opening, as investigated by microscopic analysis.

Gerlinde Lefever, Nele De Belie, Danny Van Hemelrijck, Dimitrios G. Aggelis, Didier Snoeck
Resistivity of Repair Materials for Concrete Repair Prior to the Application of a Cathodic Protection System

Suitability of repair materials for local concrete repair in combination with a cathodic protection system depends on the compatibility of their electrical resistivity characteristics with the parent concrete. As data on resistivity of repair mortars is very limited, selection of a compatible product is not always possible. In this research, the electrical resistivity of 10 different structural repair mortars was tested at three different environmental conditions (temperature of 20 °C and relative humidity of 60, 80, and 100%) by means of three resistivity test methods: four-point electrode method (Wenner Probe), two-plate electrode method and method with embedded electrodes. In this way, a database is created through which the most suitable repair mortar can be selected for each concrete structure in different environments. The relative humidity (RH) of the environment has a large influence on the resistivity of the repair products: on average, at the age of 91 days, a decrease of the RH of 20% tripled the resistivity of the repair mortars. Furthermore, based on the obtained results it is expected that this effect will be even larger on the long term (e.g. after several years). The two bulk resistivity methods showed comparable results. However, the two-plate electrode method was found to be unsuitable for resistivity measurements of non-saturated mortar specimens. The surface resistivity, measured by the Wenner Probe, was found to be a factor of 4 to 5 times higher compared to the bulk resistivity. The difference can mainly be attributed to the small size of the specimens used in this research.

Bjorn Van Belleghem, Mathias Maes, Tim Soetens
Non-destructive Tests for Estimating the Tensile Strength in Concrete with Deep Learning

Currently, non-destructive tests (NDTs) are one of the most well-known procedures considered for monitoring concrete behavior because it is possible to short-cut laboratory experimentation time. There are many methods for estimating the tensile strength values with acceptable accuracy, although it is necessary to increase the accuracy for this parameter. This research proposes to use an artificial intelligence method to achieve this aim. Artificial Intelligence has been one of the most efficient approaches for solving engineering and material problems because of its effective performance and strength to achieve higher accuracy. This paper proposes a novel approach, using a Deep Learning model for predicting the tensile strength in concrete based on just standard non-destructive test measurements. The considered model for this research is a Deep Neural Network applied in a particular concrete mixture. This model allows predicting the tensile strength with acceptable accuracy and low computational cost. Also, it is an adequate alternative to estimate the resistance of tensile strength in several structures just by taking standard measurements like Electrical resistivity, Resonance Frequencies, and Ultrasonic Pulse Velocity. For this study, 250 concrete samples were analyzed. The model employs a Rectified Linear Unit function in their architecture as an activation function in all hidden layers, and the model contains 450 neurons. This model considers the NDTs measurements as input data, and the output value is the tensile strength. The model shows an excellent accuracy of over 96%, which is impressive. This approach showed satisfactory performance in tensile strength prediction for the concrete mixture analyzed.

José A. Guzmán-Torres, Carlos A. Júnez-Ferreyra, Ramiro Silva-Orozco, Wilfrido Martínez-Molina
A Combined Electrical and Electromechanical Impedance Study of Early-Age Strength Gain in Cement Mortars

From simple strain gauges to more sophisticated techniques such as acoustic emission and digital image correlation methods, a variety of non-destructive methods are proposed in the literature for inspecting civil structures. However, in addition to accuracy and simplicity, automation and timely data collection are the main requirements for an efficient in situ non-destructive testing technique. Electrical impedance and the electromechanical impedance tests of cementitious members, are perceived to be suitable candidates for fulfilling the simplicity, automation and accuracy requirements, hence providing an efficient yet relatively non-expensive remote monitoring system. Throughout the first 28 days of a cementitious composites age, significant gain of strength is typically developed. It is crucial during this period to characterize the in situ strength gain profile for both planning and quality control purposes. This study investigates the viability of both the electromechanical impedance technique and the electrical impedance spectroscopy technique as non-destructive strength testing methods. These were assessed against their ability to detect strength changes due to the ongoing hydration reaction in cementitious mortars conforming with BS EN 196-1:2016. Results from both techniques were compared with the compressive and flexural strengths. The electromechanical impedance was assessed in terms of the change in the electrical impedance signature response through time, which was obtained through surface attached PZT sensors. Concurrently the electrical impedance response was collected through embedded stainless-steel electrodes across the frequency range of 1–10 MHz. This study will act as a guide for selection of a suitable technique for in situ strength gain monitoring using electrical methods.

Hussameldin M. Taha, Richard J. Ball, Andrew Heath, Kevin Paine

Bituminous Materials, Polymers, Timber, Bamboo, Recycling, Masonry, etc.

Using Neutron Tomography to Study the Internal Curing by Superabsorbent Polymers in Cementitious Materials

Superabsorbent polymers (SAPs) are novel admixtures in cementitious materials in order to have internal curing. Neutron tomography is used to investigate and to visualize the water release by SAPs with different kinetics over time. This gives insight into the time window for effective internal curing as the results are linked to shrinkage and internal relative humidity measurements. One SAP showed complete mitigation of autogenous shrinkage and even a partial expansion effect (+121 µm·m−1 after two days), while another type of SAP proved to be less effective as the shrinkage (−189 µm·m−1) was more resembling a reference system with a higher effective water-to-cement ratio. The internal relative humidity after two days of hardening showed that the effective mixture still possessed a high relative humidity at 98% while the ineffective mixture had a lower internal relative humidity at 95% after 2 days. It was still unclear whether this ineffective SAP released its water too slow or too fast. The study with neutron tomography showed the necessary kinetics to mitigate autogenous shrinkage of one SAP between final setting and 30 h. However, the ineffective SAP released its water quickly after final setting and prior to 20 h, even though water is still necessary at later time intervals to mitigate further autogenous shrinkage and to maintain the internal relative humidity.

Didier Snoeck, Wannes Goethals, Jan Hovind, Pavel Trtik, Tim Van Mullem, Philip Van den Heede, Nele De Belie
Modular Lightweight Wastewater Treatment Plants Made of Textile Reinforced Concrete—Means to Reliable Wastewater Treatment in Rural Areas

The safe supply of clean water is of such prominent importance that it is even defined by the United Nations Sustainable Development Goal 6 “Clean Water and Sanitation”. In order not to lose sight of those regions, outside the conurbations, that are difficult to access, wastewater treatment plants (WTP) must adapt to new requirements. As a novel material, textile reinforced concrete (TRC) opens up new possibilities to ensure the treatment infrastructure. A solution that can be used on a large scale requires consideration of the composite material, adaptation of the structure design to the requirements of material, process and load as well as the economic consideration of manufacturing, distribution and sales. The focus here is on a modular product solution. In this way, the low weight of the TRC components in transport can be fully utilised. The operating loads are defined in accordance with conventional WTPs. The life cycle loads from production to operation are included in the structural simulation and design development. Based on this, the requirements for textile reinforcement and concrete are deduced. Both single components as well as the composite material are evaluated with mechanical testing, regarding their suitability for the present application. Six compositions of matrices and four varieties of textiles with two different types of coatings in each were examined. TRC composites were prepared and tested for the best combination of these materials. Numerical models, based on the material and composite results, considered various practical conditions, to yield the primary configuration and dimensions of the treatment unit. The details of the steps involved in arriving at the suitable material selection and the numerical simulation are discussed in this paper.

Kira Heins, Gözdem Dittel, Komathi Murugan, Mohit Raina, Smitha Gopinath, Oliver Hentzschel, Sachin Paul, Ravindra Gettu, Thomas Gries
Influence of Textile Orientation on the Quasi-static and Repeated Loading Behavior of Textile Reinforced Cementitious (TRC) Composites

Textile Reinforced Cementitious (TRC) composites combine the compressive strength of cement and the tensile resistance of fiber reinforcements. These materials have become increasingly popular in recent years; due to their desirable properties such as high tuneability, slenderness and freedom of form they provide smart solutions for progressive building designs. Currently, a lack of research exists that tackles complex and repeated loading conditions of these promising materials. The objective of this research campaign was threefold. Firstly, the influence of the angle of unalignment between the textile reinforcement and the loading direction was investigated in quasi-static loading conditions (0°, 22.5° and 45° were considered), focusing on the TRC strength, post-cracking stiffness and crack evolution. Secondly, these parameters were investigated after repeated loading conditions. For this purpose, an experimental campaign was performed where the specimens were repeatedly loaded during N = 25 cycles between a residual stress in the pre-cracked stage and 0.5 times the failure load obtained from the quasi-static tests. Thirdly, the residual properties of the beams tested in repeated loading were characterized by means of a quasi-static test until failure.A total of 18 (500 mm × 150 mm × 15 mm) TRC samples were tested in four-point bending (three for each test series and orientation). The samples were reinforced by means of a single textile reinforcement grid, the longitudinal fiber volume fraction (Vf) was 0.74%. From the experimental results, a clear influence of the angle of unalignment on the quasi-static and repeated loading behavior of the TRCs was observed.

M. El Kadi, M. Ahmad, T. Tysmans
Compressive Behaviour of Alkali Stabilized Quarry Sludge Blocks

There is a global interest in alternative building elements that accomplish an eco-friendly fabrication process and offer economical solutions. Raw quarry sludge was a residue with no acceptable compressive strength nor well-durability performance; hence, stabilization through physical and chemical additions was performed. Alkali stabilized quarry sludge (ASQS) can contribute to the reuse of industrial mining wastes and even use them as main materials on construction prefabricated elements, aligned with the circular economy principles. This study presents the experimental validation of a previously mechanical simulation of a block with solid geometry, using ASQS as the main material. Validation was carried out through a compressive strength test. Besides, block characterization is effectuated with different standardized tests such as capillary absorption, Abrasion, and Efflorescences. Thus, it could be determined that quality block standards are not accomplished due to issues in compaction as traditional techniques are employed. This way, further research, and development must be applied to the masonry element fabrication process, seeking the achievement of a new sustainable material and an economical prefabricated element with adequate mechanical performance.

Nicolas Zapata, Andres Restrepo, Yhan Arias, Juan Ochoa
Properties of Concrete with Thermo-mechanically Beneficiated Fine Recycled Aggregates

There is a worldwide shortage of fine aggregates/sand, and recycled concrete aggregates could be an alternate source to meet the demand. However, the main problem associated with the fine recycled concrete aggregate (FRCA) is the high amount of low-density porous adhered cement paste. This, along with the presence of finer particles (<300 µm), could increase the absorption capacity of FRCA significantly. Considering this in the present study, an attempt has been made to use thermo-mechanical beneficiation, where waste concrete was heated at a temperature of 400–500 °C followed by cooling at ambient temperature, after which it is processed further with the help of a ball mill. After this, the finer particles (<300 µm) are separated to give FRCA that has been used in concrete mixtures of 40 MPa design compressive strength. The mechanical properties were found to be comparable to the reference mix with natural sand. Also, the results from durability tests show that the use of beneficiated FRCA would not significantly reduce the durability of concrete, which could be a major concern.

Rohit Prajapati, Stefie J. Stephen, Ravindra Gettu, Surender Singh
Bond-Behavior of Bamboo Strips and Bamboo/Wood Bio-Concretes

Seeking the development of light structural elements with less environmental impact, the use of bamboo strips as bio-concretes reinforcement can provide an interesting solution in civil construction. Therefore, in order to use the bamboo strip with bio-concrete, it is important to understand the bond-behavior between both materials. This paper aims to analyze the bond-behavior of coated and uncoated bamboo strips with bamboo bio-concretes (BBC) and wood bio-concretes (WBC). The coating was made with a mixture of epoxy resin and sand on the lateral surface of the strips, and its effect on the adherence with bio-concretes was analyzed through the pull-out test. The bio-concretes were produced with a volumetric fraction of 40% of bio-aggregates and characterized through uniaxial compression and splitting tests. The results showed that, after 28 days of curing, the bio-concretes presented compressive strength of 6 MPa, and a tensile strength ranging from 1.14 to 1.23 MPa for both bio-concretes. As expected, the coated strips presented a bond higher with both bio-concretes than the uncoated. Comparing the bio-concretes, the force required to pull the coated bamboo strip from the BBC was greater than that of the WBC.

Nathalia Andrade da Silva, Amanda Lorena Dantas de Aguiar, M.’hamed Yassin Rajiv da Gloria, Romildo Dias Toledo Filho
Controlled Microencapsulation of Rejuvenators by Jet Vibration to Promote Self-healing in Bituminous Materials

This study aimed to synthesise enhanced biocapsules containing oil as an additive to promote self-healing in bituminous materials. The capsules consisted of a biopolymeric matrix of sodium alginate as encapsulating material and sunflower cooking oil as a non-hazardous rejuvenating agent. Oil was incorporated in five concentrations by weight of alginate, 1:1, 1:3, 1:5, 1:7, and 1:9, respectively. Thus, five oil-in-water (O/W) emulsions were prepared to synthesise biopolymeric capsules via ionic gelation using an encapsulator device that works by jet vibration technique. The physical properties, stability and droplet size distribution were measured in the O/W emulsions using microscopy techniques and laboratory tests. The morphological and the physical-mechanical properties of the biocapsules were also evaluated. The main results showed that the O/W emulsions increased their viscosity and physical stability when increased the oil content, reducing their creaming rate over time. The synthesised biocapsules presented spherical morphology and high encapsulation efficiency. The size of the produced biocapsules was mainly dependent on the selected nozzle size, the flow rate and viscosity of the extruded O/W emulsions, and the vibrational frequency applied and controlled on the encapsulator device. A reduction in the encapsulated rejuvenator content was quantified in the biocapsules, resulting in a lower volume and higher density and compressive strength values. Finally, the capsules effectively resisted the load associated to on-site compaction in a way that they can be potentially used as an effective additive for asphalt self-healing purposes.

José L. Concha, Erik Alpizar Reyes, Jose Norambuena-Contreras
A Novel Spore-Based System with Rejuvenator Controlled Release for the Self-healing of Bituminous Materials

Self-healing bituminous materials by adaptive encapsulated rejuvenators system is a hot topic within road materials. For the first time, this work explores the natural spores for the encapsulation of rejuvenators as a novel controlled release system to promote the self-healing capability in aged bituminous materials. Treated spores were obtained from natural spores by chemical processes. To synthesize spore-based microcapsules, firstly, spores were defatted, and then the protein and cellulosic materials were removed. Spores were processed, and sunflower oil as a rejuvenator was encapsulated inside spore microcavities by encapsulating passive and vacuum loading technologies. Physicochemical and microstructural properties of the natural spore formulations were evaluated. Changes in the composition of the spores among the process were studied by FTIR spectroscopy. The microstructure analysis showed that the spores after treatment were empty, showing the complete removal of all contents inside, keeping intact microstructure, and providing large cavities for molecular loading. Furthermore, sunflower oil encapsulation efficiency into the spore cavities was considerably higher with vacuum loading than by the passive loading process. The controlled release mechanism and the healing efficiency of encapsulated rejuvenators in the spore capsules were also quantified. It was proved that the proposed approach was able to control the release of the rejuvenator with an attractive biomaterial possessing a very strong structure. The main results provide the basis for further exploration into the encapsulation of rejuvenators in natural plant spores as a promising novel controlled release spore-based system for the self-healing of bituminous materials.

Erik Alpizar-Reyes, José L. Concha, José Norambuena-Contreras
Permanent Deformation Characteristics of Hot Recycled Blends of Three Different RAP Sources

As the road networks are expanding worldwide, recycling pavements, both flexible and rigid pavements, is an important area of research nowadays. To achieve the sustainability objectives in the road construction industry, extensive research focused on reclaimed asphalt pavement (RAP) is required. Rheological parameters like Superpave stiffness parameter (G*/sinδ), true high PG temperature (PGH), and Zero Shear Viscosity (ZSV) have been widely used to study the permanent deformation characteristics of asphalt binder. The experimental campaign includes three RAP sources (RAP-D, RAP-UP, and RAP-UK) and one Recycling Agent, RA (soft binder grade VG-10). The proportion of RAP binder in total binder was 0%, 15%, 25%, 40%, 65%, 80%, and 100% (RAP binder) by weight of total binder. It was found that for highly aged RAP source having PGH of 154 ℃, the linear blending chart concept is not applicable. Similarly, the tiered approach of RAP incorporation was found to over-predict the minimum RAP content when the RAP binder is highly aged. For the three RAP sources, it was observed that a log-linear relationship can improvise the conventional log-log relationship between PGH and ZSV. The same was verified with the statistical analysis and using a scatter plot of matrices (SPLOM). The effect of RAP content on mixing and compaction temperature of the hot recycled mix was analyzed based on the equi-viscous approach.

Ankit Sharma, Dheeraj Adwani, G. D. Ransinchung R.N., Praveen Kumar
Influence of Treated Mixed Recycled Aggregates in Concrete Properties

Extensive construction and demolition waste (CDW) is generated during the construction process. That waste is currently deposited in landfills. It is necessary to produce and employ mixed recycled aggregates (MRA) in low strength (up to 30 MPa) concrete elements. This study aimed to describe the properties (physical, mechanical and durability) of concrete made with treated (employing water glass, WG5, and silane admixture, Si6) MRA aggregate compared to untreated recycled concrete. Two types of MRA aggregates (with different amounts of ceramic particles) were employed. The concretes used 100% coarse and fine recycled aggregates with 300 kg of cement and an effective water/cement ratio of 0.50. These concrete mixes were suitable for use as 25 MPa concrete. The concrete produced with MRA aggregates with the WG5 surface treatment achieved the desired strength for reinforced concrete of 30–35 MPa. However, all the concretes obtained a low value of the elastic modulus. Although all the concretes manufactured with 100% recycled aggregate met the EHE requirements (Spanish Standard of Structural Concrete, EHE) regarding the depth of water penetration under pressure and relatively low carbonation coefficient, the drying shrinkage was high. However, the surface treatments of aggregate reduced recycled concrete shrinkage considerably.

Miren Etxeberria, Carla Vintimilla
Use of Corncob Granules as Sand Replacement in the Production of Cement Mortars

Low-cost housing is urgently needed in low- and middle-income countries. Concrete is often too costly and raw material production, including aggregate extraction, is known to be harmful to the environment. In this paper the use of an agricultural waste, corncob, as a potential lightweight replacement of sand in cement materials has been studied. Corncob granules were added to the mix in percentages of 5%, 10%, 15% and 20% by volume. The corncob granules were used in their natural state as well as following coating with either cement slurry or gum Arabic. The effect of sand replacement was determined through flexural and compressive testing of materials, while the chemical composition was evaluated using Thermogravimetric Analysis (TGA) and X-Ray Diffraction (XRD). The porosity of the mixes was also determined using a mercury inclusion porosimeter (MIP). The results showed that while the early age strength (7 days) was extremely low, the late age’s strengths improved drastically between 10% up to 3500% in 28 days.

Taghried Abdel-Magid, Pete Walker, Kevin Paine, Stephen Allen
Properties of High-Performance Concrete with Coarse Recycled Concrete Aggregate for Precast Industry

Nowadays, industrially produced high-quality coarse recycled concrete aggregate (RCA) complying with NEN B 15-001 Type A + are available in Belgium. The Flemish precast concrete industry is interested in incorporating such RCA in concrete products to enhance competitive advantages. This paper provides a feasibility study of using the commercial RCA to develop high-performance concrete (HPC) for structural precast concrete elements. The coarse natural aggregate was partially or fully replaced by RCA with a similar particle size distribution, and the replacement percentages were 0%, 30%, 50% and 100% in volume. The physical and mechanical properties and durability of concrete were tested. The results indicated that the incorporation of RCA had different effects on the various properties of concrete. It is feasible to produce HPC with RCA when concrete is appropriately designed and produced.

Xiaoguang Chen, Hanne Vanoutrive, Elke Gruyaert, Jiabin Li
Artificial Rocks Made from Dredged Sands of the Magdalen Islands (Canada): Preliminary Study

The consumption of natural materials for construction purpose is increasing each year while the resources are limited. To reduce the environmental burden and efficiently optimize resources, the use of local and alternative resources as building materials is necessary. This solution is not always convenient, especially for the isolated places like islands, and the Magdalen Islands in Quebec are not an exception. Those islands are currently in a shortage of granular materials and must import them, which represents considerable economic and environmental costs. The general goal of this contribution is to take advantage of the local dredged sands, to be reused in civil engineering infrastructures. This study explores the feasibility of consolidated sandy sediments as an artificial rock, which may serve as mass elements for coastal protection against erosion.

Amine El Mahdi Safhi, Patrice Rivard, Mahfoud Benzerzour, Nor-Edine Abriak
Proceedings of the 75th RILEM Annual Week 2021
herausgegeben von
J. Ivan Escalante-Garcia
Pedro Castro Borges
Alejandro Duran-Herrera
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