Proceedings of the RILEM Spring Convention and Conference 2024

Inhaltsverzeichnis

1. Durability and Innovative Materials

   1. Frontmatter

   2. Advancing Corrosion Resistance of Steel Fibre Reinforced Concrete in Railway Construction

      Kangkang Tang

      Abstract

      Steel fibre reinforced concrete (SFRC) offers a promising alternative to conventional steel reinforcement when constructing railway tunnel linings due to its remarkable strength and excellent fire resistance. Nevertheless, a crucial inquiry persists: could steel fibres potentially facilitate the conduction and transmission of stray currents, resulting in corrosion similar to that observed in conventional steel reinforcement? To address this concern, instrumental methods in electrochemistry, including potentiodynamic polarization techniques, have been used to assess SFRC’s corrosion resistance. Experimental results highlight the inherent resistance of concrete reinforced with discrete and discontinuous steel fibres to corrosion induced by railway stray currents. However, it is worth noting that the presence of even a small quantity of NaCl, specifically 0.3 mol/L in the concrete pore solution, can significantly diminish its corrosion resistance.

   3. Recent Initiatives of ACI Committee 222 on Corrosion of Metals in Concrete

      Burkan Isgor, Ceki Halmen, David Trejo, David Tepke

      Abstract

      Sustainable construction of concrete structures in corrosive environments requires responsible use of locally available materials to extend services life, reduce cradle to grave carbon footprint impact, and to make these structures economical. Conservatism in setting limits for allowable chlorides in new concrete is needed to promote extended service life; however, refinement of industry approaches and standards towards protection against excessive conservatism is also important so that maximum flexibility and use of mixture supplements can be used to optimize reduction in carbon footprint and costs in construction. ACI Committee 222, Corrosion of Metals in Concrete, has recently revised the Guide to Protection of Metals in Concrete Against Corrosion. Due to the significant impact to the industry, considerable variation in existing approaches and serious consequences of corrosion, the committee has also recently promoted initiatives associated with refining chloride limit recommendations for new construction and chloride threshold testing. This includes a recent Special Publication on chloride limits, revision of recommendations in the new guide, formation of a special Task Group, and sponsorship/oversight of ACI’s Concrete Research Council (CRC) funded research for a collaborative study for the development of a standard critical chloride threshold test method. This paper will discuss some of the key updates to the Guide Document, as well as recent initiatives associated with chloride limits and thresholds. Information will be provided on the results of the CRC-funded research sponsored by the committee for a new test method for quantifying chloride limits. It will also discuss the reasons why these issues have been identified as important, impacts to the industry, and future needs.

   4. A Probabilistic Approach to Service Life Prediction: Comparing a Reactive Transport Model with the fib Chloride Model

      Annika L. Schultheiß, Ravi A. Patel, Frank Dehn

      Abstract

      Chloride-induced depassivation of steel reinforcement is one of the key durability issues for concrete structures. Conventionally prediction of service life using a probabilistic approach for chloride-induced depassivation relies on semi-empirical engineering models like the fib chloride model. However, such models use parameters such as the aging coefficient which are difficult to define in practice and introduce additional uncertainties that makes such models difficult to apply for realistic service life prediction. This study offers a new approach, employing a physics-based reactive transport numerical model in a probabilistic manner. The reactive transport model considers chemical and physical interactions within the concrete structure. Based on experimental data, a new binding isotherm for Portland cement paste is presented and used in the reactive transport numerical model. To demonstrate this approach, a case study compares the predictions made by the reactive transport model with those from the conventional fib chloride model. The reactive transport model predicts the chloride ingress after 6 years with less uncertainty compared to the fib chloride model. It also predicts the highest probability of depassivation after 50 years. Additionally, this study explores the impact of introduced uncertainties, given their substantial effect on the prediction results.

   5. Prevention of PEG-1000 Migration in Eco-Sustainable, Form-Stable Phase Change Material Included in Aerial Lime-Based Mortars

      Paulina Guzmán García Lascurain, Mariaenrica Frigione, Antonella Sarcinella, Elena Hitthaler, Luca Andena, Lucia Toniolo, Sara Goidanich

      Abstract

      Heating and cooling systems are a major contributor to global energy consumption and CO₂ emissions in the construction industry. In case of restoration of historical buildings, a possible solution to mitigate this problem is to incorporate thermal energy storage systems, like phase change materials (PCMs), into restoration mortars. PCMs, like poly-ethylene glycol (PEG), can be incorporated in lime-based mortars as bi-phased smart aggregates. These aggregates consist of a porous inert matrix, for instance small flakes of Lecce Stone, containing the active PEG phase [1]. Although mortars with PCM show favourable thermal properties, nevertheless they present a reduction in their mechanical resistance possibly due to: (i) a lack of compatibility between aggregate and binder; (ii) a lack of confinement of the PEG polymer in the stone, causing its dispersion in the mortar. Therefore, the aim of this study was to investigate the causes of the observed reductions in mechanical properties and to propose a method to prevent this occurrence. The results showed that the dispersion of PEG-1000 within the binder is apparently the main reason behind the reduction of the mechanical properties. Micro-FTIR compositional mapping evidenced that the lack of confinement of the PEG-1000 in the inert aggregates results in its dispersion inside the mortar; mechanical tests showed that the binder’s mechanical resistance is reduced in the presence of PEG. To prevent PEG dispersion, a simple coating procedure of the smart aggregates was successfully implemented. The improved confinement of the PEG-1000 in the inert aggregates produced a reduction of the internal cracks and pores of the mortar.

   6. Investigation of Natural Clays as Precursor for Geopolymers – A Preliminary Study Case

      Ilda Tole, Sidorela Vishkulli

      Abstract

      Concrete is responsible for 8–10% of total anthropogenic CO₂ emissions, with cement production accounting for over 60% of this contribution. Considering this environmental impact, the integration of sustainable and alternative materials as replacements for cement represents a promising strategy for emission reduction. Alkali-activated materials and/or geopolymers can be used as an alternative construction material and are formed by activating aluminosilicates such as fly ash, granulated blast furnace slag, and/or clays with alkaline solutions. The selection of precursors for geopolymer synthesis is strictly related to their local availability. Among these, activated clays have gained considerable attention, offering great potential for geopolymer production due to their widespread availability and composition. Albania has a great potential due to the weathering conditions, but very limited information is available. In this preliminary study case, different clays were collected from different areas across Albania and investigated for their reactivity and suitability as precursors for geopolymers after thermal treatment. These clays were subject to characterization, and their reactivity was assessed according to R3-bound water methods. Calcination of clays was performed at temperatures of 650 and 750 ℃ for 1 h. The results indicated that calcined clays from Albania can have potential to be suitable source materials in geopolymerization reactions and/or as supplementary cementitious materials.

   7. Role of Pb in Portland Cement Hydration: New Insights from In-Situ Laboratory XRD

      Yikai Liu, Maria Chiara Dalconi, Luca Valentini, Maurizio Pietro Bellotto, Simone Molinari, Gilberto Artioli

      Abstract

      Ordinary Portland cement (OPC) is a ubiquitous construction material and has long been the most prevalent of all man-made concepts. However, the massive demand for OPC is responsible for approximately 7–8% of all anthropogenic CO₂ emissions. Substituting OPC with industrial by-products presents a promising avenue for reducing clinker usage and aiding industry decarbonization. However, concerns arise regarding the presence of trace metals, particularly Pb, which can impede early hydration and degrade material properties. Understanding the kinetics of clinker phase dissolution in the presence of Pb is crucial for mitigating these issues. Conventional characterization methods may alter samples and fail to adequately capture underlying reaction mechanisms. To address this challenge, our study employs in-situ X-ray diffraction (XRD) to accurately assess Pb-OPC hydration kinetics in real time. Furthermore, we develop a geochemical model to quantify hydration reactions. This model supplements experimental findings, providing valuable insights into the proposed mechanisms. Overall, our work enhances the understanding of Pb-OPC interactions in cementitious materials, ultimately contributing to more efficient industrial by-product management and sustainable construction practices.

   8. Durability Study of Concrete with Calcinated Clays – Experiences in Guatemala After Four (4) Years

      Plinio E. Herrera, Ariel Osorio, Hans Calel, Roberto Díaz, Luis Velásquez, Elvis García

      Abstract

      The present work evaluates the performance of concrete, after four (4) years of placement in slabs on ground in Guatemala City, produced with the first LC3 [1, 2] Limestone-Calcined Clay cement in Guatemala, compared with concrete produced with a High Early Strength Portland Pozzolanic cement, commonly used in Ready Mix applications in the country. Three different concretes were evaluated: 1 with Portland Pozzolanic Cement (cement content of 292 kg/m³), 2 with LC3 (cement content of 292 kg/m³), and 3 with LC3 (cement content of 352 kg/m³). As expected, the Portland Pozzolanic cement concrete and the LC3 cement concrete with higher cement content, present much better compressive strength than the LC3 cement concrete with 292 kg/m³ cement content, especially at early ages. In durability tests, both concretes with LC3 cement present higher carbonation depth than the Portland Pozzolanic cement concrete. Nevertheless, both concretes with LC3 have a superior performance in resistance to chloride ion penetration. It is noted, that on a long-term basis, the Portland Pozzolanic Cement concrete improved considerably on this particular test, due to pozzolanic reaction. Although more tests are needed on concretes with LC3 cements, for the moment, and with the humidity conditions prevailing in Guatemala City, which are moderate, around 70%, and very prone to carbonation, it is recommended to continue to use concretes with Portland Pozzolanic cement. On the other hand, due to the good performance of concrete with LC3 cement on the chloride ion penetration test, this cement is recommended in high humidity environments, where carbonation is not an issue.

   9. Durability of Mg-Based Binders – Resistance Against Chlorides, Moisture and Corrosion

      Fabio Enrico Furcas, Alexander German, Frank Winnefeld, Ueli M. Angst

      Abstract

      MgO/hydromagnesite blends have emerged as promising low-carbon alternatives to conventional building materials based on Portland cement. Despite recent advancements in the characterisation and modelling of Mg-bearing phases in this type of binder, the durability of building products, i.e. mortar and concrete, has received comparatively little attention. This study investigates the ability of MgO/hydromagnesite binders to resist chloride and moisture ingress and to protect embedded steel from corrosion. A combination of chloride-resistance, impedance and linear polarisation resistance measurements is used. Irrespective of the curing conditions, 90/10 mass-% MgO/hydromagnesite mortars feature a low chloride diffusion coefficient of \(D=\left(0.6\pm 0.3\right)\times {10}^{-12}\) m²/s. Single frequency impedance measurements between stainless steel bars embedded in mortar prisms suggest that the mortars are resistant to the ingress of water, prospectively due to their dense microstructure. Embedded carbon steel bars exposed to the ingress of water and concentrated chloride-containing solutions experience low corrosion current densities in the order of 10^–7 to 10^–8 A/cm², similar to the corrosion rate of passive steel in concrete. Even though the pore solution in the MgO/hydromagnesite binder is buffered at significantly lower pH (10.5–11.0) than the aqueous phase in equilibrium with portlandite in Portland cement, the novel binder could thus be used for reinforced cement products. Further testing is needed to assess the long-term stability as well as the corrosion rate of steels embedded in MgO/hydromagnesite building materials under the simultaneous ingress of moisture and CO₂.

   10. Carbonation Treatment of RCA Concrete: A Preliminary Investigation

       Nicoletta Russo, Federica Lollini

       Abstract

       Strategies to reduce the environmental impact of the concrete industry include enhancing the CO₂ sequestration using the material as a durable carbon sink. At this aim, early-age carbon curing has been proposed and seems to be a promising method for CO₂ sequestration. However, studies on this treatment are still limited and do not allow to clearly evaluate its environmental benefits and its effects on concrete properties. In this work, both moist and carbon curing treatments were performed on concretes made with natural aggregate (Ref) and recycled concrete aggregate (RCA). In particular, concretes were either moist cured for 7, 14 and 28 days or carbon cured for 7 and 14 days. In addition, combined curing was also tested, performing carbon curing for 7 and 14 days, followed by moist curing up to a total of 28 days. After the different curing times, compressive strength, modulus of elasticity and resistivity were measured, together with the carbonation depth by means of phenolphthalein test. At all the curing times the use of RCA in partial replacement of natural aggregate led to a slight worsening of the mechanical properties. The carbonation treatment both in Ref and RCA concretes allowed to permanently store the CO₂ guarantying comparable performances. Moreover, the combined curing had a beneficial effect in partially restoring the alkalinity of the cement paste.

   11. Proposal of a Phase Change Material-Graphene Modified Composite with Enhanced Thermal Properties for Application in Energy Storage Concrete

       Mahsa Salimi, Luigi De Nardo, Valter Carvelli

       Abstract

       Phase change materials (PCMs) are among the most promising candidates for thermal energy storage (TES) applications. However, their low thermal conductivity and slow phase change phenomena are major restricting factors for efficient TES applications. This work investigates a novel thermal energy storage aggregate (TSA) composite based on butyl stearate (BS), a low-cost, commercially available, supported by graphene nanoparticles (GN) as high conductive agents stabilized in the porous media of expanded clay (EC) aggregates. Based on GN's high thermal conductivity, adding 2% GN in the composite shows enhanced heat transfer, while the composite TSA containing 2% GN, compared to plain EC, decreases the maximum temperature peaks up to 5 ℃ in heating cycles. Furthermore, the leakage test demonstrates that the developed TSA exhibits excellent thermal stability, indicating the potential to maintain its thermal performance even after multiple thermal cycles. Finally, the thermal performance of a TES concrete (TSC) containing TSA with 3.5% PCM-2GN by weight of TSC decreased the peak ambient temperature fluctuations up to 3.5 ℃ for a test in complete insulation condition. This reduction on TSC surface was between 9 ℃ to 10.8 ℃ in 1D heat transfer condition with 0% and 50% humidity, respectively. The novel-designed TSA composites pave the way for a practical and effective solution to enhance internal building comfort and energy efficiency.

   12. Effect of Ion Concentration in the Mixing Water on Performance and Hydration Kinetics of Cement-Based Materials

       Olcay Gürabi Aydoğan, Alphan Ali Dilber, Arda Sepetçi, Muhittin Tarhan, Nilüfer Özyurt

       Abstract

       Concrete is the most widely used man-made material in the world. Globally, millions of tons of drinkable water are used each year in the production of concrete and its derivatives. Considering the regional and global water shortages in recent years, it is considered that this consumption should be restricted urgently. Seawater is considered one of the alternative mixing waters that could be used as a substitute for fresh water. The interest in this subject has increased in recent years and the number of research projects on the use of seawater as the mixing water for concrete considerably increased. Most of the publications deal with the mechanical performance and microstructure of seawater concrete. Although there is consensus among researchers on some of the obtained results, there are many points where contradictory results have been reported. In this study, the effects of different mixing waters, ion concentrations, and metakaolin substitution on the performance and hydration kinetics of cement-based materials were investigated. The results showed that the dissolution of binder ions improved with higher ion concentrations. In addition, the synergistic effect of metakaolin and seawater maximized the performance and hydration kinetics of the material.

   13. Influence of Carbonation on the Chloride Ingress Analyzed via Optical Sensors

       Marlene Sakoparnig, Bernhard Müller, Karl L. Sterz, Isabel Galan

       Abstract

       Comprehensive understanding of the processes of chloride ingress and carbonation, particularly their combined effects, is imperative to find prevention strategies. In this study, 3 mortar samples (CEMI+ground granulated blast furnace slag) were exposed to three alternating 14 day cycles in a 3% NaCl solution and a carbonation chamber (3 vol% CO₂, 65% RH). After each cycle one sample was taken out for analysis. The water- and the acid-soluble chloride content was determined in powdered samples using a novel optical chloride sensor and via titration (reference method). The pH determination and assessment of the carbonation progress was done via optical pH imaging together with phenolphthalein coloration, as reference method. The results revealed a relatively constant carbonation rate ranging between 0.6 and 0.7 mm/√d. The pH imaging visually depicted the carbonation progress with depth and provided pH profiles in the pH range of 7.0–12. The chloride content decreased in the carbonated zone and the region with the highest chloride concentration shifted inwards. The results show a good correlation of the new optical sensors with the reference methods. Notably, optical pH imaging provides more insights into the pH variations over time compared to the phenolphthalein method. This investigation contributes towards advancing our comprehension of corrosion processes, particularly in the context of combined attacks involving carbonation and chloride ingress. The robust correlation observed between optical sensors and established methods highlights the potential of optical sensing technologies in enhancing our ability to monitor and understand corrosion phenomena in concrete structures.

   14. Non-destructive Testing for the Determination of Durability-Relevant Material Properties of Clinker-Reduced Building Materials

       Thilo Bintz, Sabine Kruschwitz

       Abstract

       In the quest to combat climate change, the construction industry, heavily reliant on cement-based materials, faces scrutiny due to significant CO₂ emissions, mainly from clinker production. To address this, there's a need to strategically reduce clinker content in cement. However, these new formulations must meet the same requirements as the original ones, so their durability must be investigated. In this study, we determined material parameters that enable an assessment of moisture and ion transport. These methods offer advantages over conventional approaches, including non-destructiveness, reduced measurement time, simplified setup, enhanced resolution, and improvement of detection limits. Our investigation utilizes NDT techniques, using ¹H NMR relaxometry for moisture transport and LIBS for ion transport in various clinker-reduced materials. The NMR tomograph provides spatial insights into internal moisture transport, correlated with weight change assessments for the capillary transport coefficient. Additionally, based on NMR relaxometry data the chloride diffusion coefficient is estimated. Chloride migration tests are performed, and results are evaluated using LIBS and indicator tests for the chloride migration coefficient. Our findings highlight NMR relaxometry and LIBS advantages over conventional methods, showcasing superior spatial resolution, non-destructiveness, and, in some cases, expedited results with independence from the formulation of the cement matrix. Thus, these new methods can be used to test the durability of new, more heterogeneous cement-based building materials and compensate for the disadvantages of conventional methods.

   15. Study on the Predictability of Carbonation Resistance of Cementitous Materials Based on NMR Features and the Use of SLAMD

       Sarah Munsch, Melissa Telong, Lili Grobla, Katrin Schumacher, Christoph Völker, Kaleb Yared, Sabine Kruschwitz

       Abstract

       This study explores the acceleration of material design in the concrete industry, focusing on improving carbonation resistance, a key factor in the durability of concrete structures. Traditional tests for carbonation resistance are lengthy, but with the construction industry aiming for sustainable production, finding a balance between carbonation resistance and CO₂ footprint is crucial. Our research employs two innovative methods:

       1.

       Applying the Sequential Learning App for Materials Discovery (SLAMD), an AI materials design framework, to an extensive dataset of real-world concrete compositions to selectively test materials that meet market demands: maximum durability, optimal eco-durability, and the best cost-durability trade-off.

        

       2.

       Investigating ¹H Nuclear Magnetic Resonance (NMR) relaxometry as a quick alternative for characterizing carbonation behavior, as it saves time compared to traditional tests and assesses the complete material's pore space. Specific NMR features are then integrated into the material design model, with the model's performance compared against traditional approaches.

        

       The results of our study are compelling, demonstrating that materials can be precisely tailored to meet specific requirements with minimal data points. This marks a significant stride in the concrete industry, indicating that NMR-based, low-fidelity surrogate characterizations, combined with a focused, data-driven design approach, can substantially accelerate the development of durable, sustainable concrete mixtures.

   16. Comparative Analysis of the Microstructure of Carbonating Cement Paste Using Proton NMR Relaxometry and MIP

       Rui Zhang, Shiju Joseph, Özlem Cizer

       Abstract

       This study investigates microstructure evolution of carbonating cement paste under varying water-to-cement ratios (w/c) which is an important parameter impacting initial porosity and pore structure that will in turn influence the carbonation process. Cement samples with different water-to-cement ratios (w/c) ranging from 0.4 to 0.6 were exposed to natural carbonation at 20 ℃ and 65% relative humidity. The microstructure was characterized using MIP and Proton nuclear magnetic resonance relaxometry (¹H-NMR). Under saturated conditions, ¹H-NMR is able to determine a wider range of pore size distribution from capillary pores to gel pores, and even interlayer spaces typically less than 1 nm. Classical Mercury Intrusion Porosimetry (MIP) is always associated with systematic errors stemming from ink bottle effects, while the external pressure from the device can also induce changes in the microstructure. By applying ¹H-NMR these problems can be mitigated, leading to more repeatable results. Results show that NMR offers a more efficient means of monitoring and studying the effects of carbonation on microstructure. Thermogravimetric Analysis (TGA) is also employed to determine the correlation between microstructural changes and carbonation degree.

   17. Soil pH KCl Measurement Correlates with the Strength of Tropical Earth Mortar

       Lily Walter, Gildas Medjigbodo, Yannick Estevez, Laurent Linguet, Ouahcene Nait-Rabah

       Abstract

       Tropical regions like French Guiana need local, sustainable construction materials to meet the increasing demand for urbanisation. Earth construction, composed of local soil and additives, is gaining increasing attention due to its minimal environmental impact, local availability, and full recyclability. One of the major limitations of earth construction is the high variability of soils. This results in unpredictable mechanical strengths and prevents its widespread industrial use. Therefore, new methods for the rapid identification of suitable soils are required. This paper explores whether several properties of tropical soils could help predict the mechanical strength of associated mortars. Particle size, major oxide composition, infrared spectroscopy, methylene blue value, and soil pH measured in water or potassium chloride (pH KCl) were characterized in nine different soil types. The nine soils were composed of kaolinite clay, iron, and aluminium oxide. Results showed that the mechanical strength of tropical soil mortar was correlated with the soil iron and aluminium oxide content. Importantly, the pH KCl, an easily measurable soil property, was also highly correlated with the soil iron and aluminium oxide content and, consequently, strongly correlated with the compressive strength (R² = 0.95). Overall, this study shows that the pH KCl can be used to predict the compressive strength of mortars made with tropical soils composed of kaolinite clay, iron, and aluminium oxide.

   18. Leaching Behaviour of Sodium Carbonate-Activated Slag/Ash Matrices Encapsulating Spent Nuclear-Grade Ion Exchange Resins

       M. Jimena de Hita, María Criado

       Abstract

       Spent ion exchange resins are a waste that is generated in the operation of nuclear power plants. These resins are usually managed by their immobilisation in cementitious matrices, specifically based on Portland cement. In this context, alkali-activated cements (AACs) emerge as a promising and more sustainable option for resin immobilisation.

       This study evaluates the leaching behaviour of AACs containing spent resins (7.5 wt.% by binder). These resins are saturated in a solution consisting of boric acid, cobalt chloride, nickel nitrate, strontium chloride, cesium chloride, and copper sulphate. The AAC evaluated is based on blast furnace slag and fly ash. Sodium carbonate (8 wt.%) is used as an alkaline activator as its utilisation reduces the environmental footprint of the cementitious material. This matrix is compared with a reference Portland-based matrix currently employed for resin immobilisation. To evaluate the confining capacity of the systems a semi-dynamic leaching test is carried out according to ANSI/ANS 16.1-2019.

       Results indicate that the reference matrix has a higher calcium leaching ratio (12 wt.% by binder) compared to the AAC (3 wt.%), suggesting a potential higher gel degradation of the reference system. The AAC matrix also shows improved strontium retention compared to the reference, whereas the reference matrix exhibits higher boron retention. Additionally, after a 90-day leaching test, AAC demonstrates significantly better mechanical development than the Portland cement-based reference. Micrographs show a region affected by the leachant of around 200 µm, however, EDX results indicate no compositional alteration of the gel in that region.

   19. Rebar Corrosion Resistance of Ultra-High Performance Concrete in Presence of Crack and Bacteria

       Maria Cruz Alonso, Pedro Serna, Paula Garcia-Fraile, Aurora Marin

       Abstract

       The paper studies the effect of the presence of cracks on the corrosion of the reinforcement in Ultra High Performance Concrete (UHPC) and the self-healing capacity of this concrete through the use of bacteria, thus protecting the reinforcement. Furthermore, the influence of the presence of steel fibers in the matrix has been analyzed. UHPC samples with two embedded bars have been used to analyze the corrosion response of the reinforcement in crack state that reaches the level of the bar. Samples with and without steel fibers and with and without bacteria were considered. The samples were exposed in a chloride environment and the corrosion response has been monitored for more than 9 months. The initiation and propagation of corrosion have been analyzed through periodic measurement of the corrosion potential (E_corr) and the corrosion rate (V_corr). The chloride profile at the crack level and the self-healing of the crack have also been analyzed.

       In UHPC the incorporation of high doses of fibers slightly affects the initiation and propagation of corrosion due to the different morphology and size of the cracks. A slightly higher corrosion rate occurred in the samples with bacteria compared to similar samples without bacteria even though the crack width was double in the case of the specimen with bacteria (160 and 85 μm respectively). The autogenous self-healing capacity of UHPC masks the contribution of bacteria to the enhancement of autonomous self-healing.