Proceedings of the 17th International Conference on Alkali-Aggregate Reaction in Concrete

The Stiffness Damage Test (SDT), a cyclic test in compression, is considered as a reliable tool for assessing concrete structures affected by ASR. Depending on the extent of ASR damage in concrete, loading levels up to 40% of the compressive strength may contribute to increasing internal damage during testing. Nevertheless, previous research found that no additional damage was induced by the SDT. This confirmed the non-destructive character of the SDT making it valid to determine the compressive strength on the same test specimens following the SDT.However, other research suggests that loading levels above 15% of the compressive strength could lead to load-induced damage in the first load cycle. The implication of the non-destructive character and the loading level of the SDT needs more attention, especially when testing anisotropically ASR-damaged concrete structures.This paper thus presents a critical evaluation of the non-destructive character of the SDT by utilizing Acoustic Emission (AE) measurements. The SDT was used to evaluate an ASR affected concrete structure after 60 years in use. Several cores from cantilever slabs were extracted enabling damage assessment of the concrete structure in use. AE allowed to measure crack occurrence with a higher accuracy. Therefore, the critical load level could be more accurately identified using AE. The magnitude of enhancing internal damage during the SDT is related to the extent of ASR. From this study it can be concluded that the non-destructive character of the stiffness damage test depends the critical load level in relation to the internal degree of damage, which can be determined by means of Acoustic Emission.

Concrete sleepers are facing premature failures in Brazil due to internal swelling reactions (ISR), a challenge that has compelled the replacement of over one million sleepers in a major Brazilian railroad, reducing their lifespan by 1/3. This study investigates four groups of sleepers at different ISR distress levels, employing various non-destructive testing (NDT) techniques. Additionally, specimens extracted from these sleepers were also subjected to thorough condition assessment (i.e., microscopic and mechanical) to estimate the degree of damage accurately. The results obtained indicate that while traditional NDT methods have limitations in assessing distinct damage degrees, a combination of surface resistivity and resonant frequency tests enhances the early detection of ISR damage. In conclusion, NDT methods have limited potential to aid routine inspection. Once potential damage is identified, it is essential to conduct comprehensive multi-level assessments to diagnose the damage (i.e., cause and extent), supporting the management of ISR-damaged sleepers.

One of the factors influencing ASR is temperature and researches have been done on relating temperature and ASR expansion. However, the relationship between temperature, ASR expansion and damage is still not clearly understood. Additionally, non-destructive testing (NDT) methods have proven that they can be used in detecting ASR in mortar and plain concrete. In this context, this research aims to use NDT to monitor damage induced by ASR in concrete with a goal of establishing a relationship between temperature, ASR expansion and damage. This aim was achieved by experiments of ASR in plain concrete cylindrical specimens exposed to temperatures of 20, 38 and 60 ℃ while fully immersed in water. The specimens’ expansions were measured by a length comparator. The damage was monitored by NDT methods of linear vibration analysis, resistivity and permittivity. The results showed a rapid ASR expansion at 60 ℃ from beginning while at 38 ℃, a latent expansion at first then rapid expansion later can be observed. The static and dynamic elastic modulus were sensitive to ASR damage as they reduced with ASR progression compared with compressive strength that did not show a reduction with ASR development. In electromagnetic tests, permittivity was found to be more sensitive to the detection of ASR compared with resistivity. The monitoring is still in progress and final results will be used in ASR modelling towards developing better monitoring for concrete structures affected by ASR.

Several non-destructive tools (NDTs) have been developed for the appraisal of ASR-induced deterioration in affected concrete, but the high variability in results has limited their use. Nevertheless, the dynamic resonance frequency has proven to be promising. The efficiency of the dynamic resonance frequency in monitoring the development of ASR in affected concrete is evaluated herein. To carry out a robust assessment of the tool, cylindrical concrete specimens containing very highly reactive coarse aggregates were conditioned at different temperatures over one year. Length and mass change, as well as the dynamic modulus of elasticity for all exposure conditions, were observed over time. The results confirm the usefulness of the resonance frequency for predicting the occurrence of ASR-induced damage particularly at high expansion levels. Furthermore, the effectiveness of the tool in predicting the progress of the reaction was evaluated by comparing its results with microscopic assessments of the ASR-affected specimens.

Several characterization techniques have been used to assess ASR-induced deterioration as a function of its development. Amongst those, promising results were obtained via scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), and resonant ultrasound spectroscopy (RUS), to evaluate the morphology and composition of reaction products and the presence of inner defects and changes in viscoelastic properties, respectively. Although SEM-EDS has been ever since well recognized as a powerful tool to detect the presence and composition of ASR-products, the evaluation of its association with induced deterioration is typically purely qualitative. This work aims to quantitatively appraise ASR-induced products and associated deterioration by the coupling of SEM-EDS and RUS, particularly a version thereof called SIngle MOde RUS (SIMORUS). Concrete mixtures incorporating a highly reactive coarse aggregate were cast and stored in conditions enabling ASR development. At 4, 11, 16, 24 and 36 weeks, the samples were prepared and characterized with the mentioned techniques. Quantifications of ASR-induced deterioration parameters (i.e., dynamic linear Young’s and shear moduli, and the respective wave amplitude attenuation coefficients, WAACs) as well as products composition were obtained. Here, we provide a preliminary discussion about the ASR secondary products’ composition along with the ability of SIMORUS to evaluate the ASR-induced deterioration derived from highly reactive coarse aggregates.

Several degradation mechanisms can affect concrete, and the alkali-silica reaction (ASR) is considered one of the most worrying. Several techniques and procedures have been developed during the last decades to assess concrete infrastructure affected by ASR. Among them, structural health monitoring techniques are considered the most reliable to understand the expansion rate over time and to predict the potential damage in affected structures. In this context, fiber optic sensors inscribed with Bragg gratings (FBG or Fiber Bragg Grating) have been gaining more attention for applications in structural monitoring. These optical sensors have small dimensions, low signal loss, and high precision for strain measurements. However, the application of FBG in degraded concrete is incipient. Therefore, this work aims to evaluate the efficiency of FBG for strain determination compared to traditional techniques. The expansion measurements taken by the optical sensors on the sample's surface showed statistically equivalent expansions with lower errors than those obtained in traditional studs’ measurements. This result demonstrates the reliability of using optical sensors for long-term monitoring of concrete structures and would allow a better investment in the repair of works, ensuring the integrity of the infrastructure of dams, bridges, viaducts, tunnels, walkways, and large buildings.

Gas-permeability has been proved useful to monitor the evolution of damage in concrete specimens subjected to mechanical loads. This paper describes the use of air-permeability to monitor and evaluate the damage caused by Alkali-Silica Reaction (ASR), in Argentina and Switzerland. In both cases, a standard NDT to measure the coefficient of air-permeability kT ‘in situ’ was applied. The data originated in Argentina correspond to observations conducted on laboratory specimens stored under controlled conditions and of large concrete blocks, some plain, some fiber-reinforced, made with reactive aggregates and containing 2.8 and 4.0 kg/m3 of Na2Oeq. The blocks were exposed outdoors to a mild climate and monitored for a period of 3.5 years, measuring kT, expansion and cracks width and density. The data originated in Switzerland were the result of condition assessment of real structures affected by ASR-related damage. The results indicate that measuring kT is useful to anticipate the formation of cracks, as the Argentine results showed that the increase in permeability happened before cracks became noticeable, probably detecting incipient micro-cracking. On the contrary, once the structure becomes visibly cracked, the vacuum-based test method either could not be applied or did not prove particularly useful, due to the resulting heterogeneity.

Digitization of established quantitative visual inspection (i.e., cracking index - CI) protocols have been evaluated. Datasets to train machine learning models are limited, and even more so for quantitative purposes. Automation of the CI has revealed some primitive challenges at the data collection stage. Therefore, this work focused on an image acquisition and processing standard approach to ensure valuable quantitative data can be extracted from the images. The anisotropy of laboratory made concrete blocks was further captured through image analysis which sheds light on the need to quantify anisotropy to efficiently select coring locations/configurations that best captures damage through further testing. This work showed that digital images can provide CIs similar to those obtained directly from the concrete surface provided that a certain resolution is kept. Moreover, the anisotropic behaviour was observed through a divided CI where cracks preferentially follow the reinforcement and through crack orientations from image analysis.

Several degradation mechanisms of concrete structures shall be investigated to define Ageing Management Programs (AMPs) of Nuclear Power Plants (NPPs). With many NPPs considering life extension and long-term operation, understanding and mitigating the consequences of Alkali-Aggregate Reaction (AAR) has become paramount.After identifying the need to assess the consequences of AAR and to find a way to take into account these consequences in the assessment of structures, CNSC staff established an extensive research program to cover the analytical and experimental sides of assessing existing concrete structures. The goal of the research program was to provide technical support for developing an independent regulatory position regarding the condition assessment and the acceptance criteria for concrete structures subjected to the AAR phenomenon. The main results show that, compared with the reference shear wall, the ductility of the AAR-affected shear wall was significantly lower, and the ultimate capacity was slightly higher. The results of the experimental program were further used as input data for the numerical simulation benchmarks performed during Phases II and III of the three-phase Assessment of Structures Subjected to Concrete Pathologies (ASCET) international project of the Nuclear Energy Agency (NEA). It was shown that the peak strength of the walls was predictable, but losses of ductility were difficult to model.This paper will first present the holistic approach undertaken to assess the properties of concrete specimens subjected to accelerated environmental conditions at the material and structural levels as well as the numerical simulations performed. The results of the benchmarks of the ASCET project will be discussed further. A brief conclusion will sum-up the overall pertinent outcomes.

The impact of alkali-silica reaction (ASR) on the physical, mechanical, and structural behaviour of ASR-damaged structures in service is time-dependent. While destructive examinations of ASR-damaged structures in service offer a valuable snapshot of the structure’s condition at a particular point in the ASR deterioration process, they cannot provide a complete understanding of how the propagation of ASR cracking affects the physical, mechanical, and structural behaviour of the structure over time. To better understand the influence of ASR on structures affected by this deleterious reaction, it is essential to conduct laboratory experiments that simulate the progress over time. These experiments can provide insights into the impact of ASR cracking on the physical and mechanical behaviour of reinforced slabs. To assess ASR-affected bridge slabs in Denmark, it is crucial to consider the time-dependent impact of external alkali supply in the assessment methodology. While the equivalent Na2O content in older Danish bridge slabs is believed to be below the threshold value for initiating ASR, it is essential to recognize that external alkali sources, such as de-icing salts, may be critical for initiating ASR damages in reinforced bridge slabs in service. To address this gap, this study aims to improve understanding of the time-dependent influence of ASR on the physical and mechanical properties of reinforced slabs through accelerated laboratory exposure. Seven reinforced slabs were cast and stored under accelerated conditions, with three exposed to saturated NaCl solution from the top surface to simulate external alkali supply, two with initial high alkali content boosted by NaOH, and two as control slabs. Internal and surface expansion measurements were periodically taken, and cores were drilled and tested in compression. Fluorescent epoxy was impregnated into the cores to evaluate ASR crack extent and orientation.

In the context of Alkali-Aggregate Reaction (AAR), the presence of water has a significant impact on the chemical reactions involved, making it challenging to predict and evaluate the transport properties of affected concrete. Air permeability is a particularly sensitive indicator of damage induced by AAR, and the characterization of this property is crucial for reducing the risk of interaction between the fluid, the cement paste, and the new products formed during AAR.This paper demonstrates that specimens subjected to AAR undergo swelling in three phases: a latent phase, an acceleration phase, and a deceleration phase. Early swelling leads to significant crack opening, rendering the material permeable to air flow despite its high moisture content. As the expansion continues, permeability increases and is primarily driven by the crack network created, although a small portion is filled by hydration products. This is further highlighted by drying kinetics, which slow down at high expansion rates.

Mass concrete specimens, consisting of concrete cores drilled in various directions from large blocks cast in the laboratory, were stored under conditions favorable to the development of ASR (38 ℃; 100% R.H.). The test specimens were obtained by drilling in either the vertical or horizontal direction of the blocks, in view of highlighting a potential influence of the presence of flat and elongated coarse aggregate particles, which may tend to orient preferentially in the fresh concrete during placement. In groups of six, the specimens were removed from their conditioning environment upon reaching selected levels of expansion to perform compressive strength tests, Stiffness Damage Tests (SDT), and petrographic examinations. As expected, the expansion data show a strong anisotropic character. The evolution of the SDT output parameters was found to be isotropic for expansion levels below 0.20%, and anisotropic above this threshold.

This research investigates the mechanical properties of concrete deteriorated by alkali-silica reaction (ASR). In contrast to the compressive strength and modulus of elasticity that are usually studied, this study mainly examines detailed fracture properties in the post-peak region beyond peak load aiming to discern the effect on post-peak behavior due to ASR-induced deterioration. Rectangular concrete specimens were subjected to a monotonic uniaxial compression test, and the study evaluated terms of different types and sizes of reactive aggregates and the effect of the Teflon sheet. Digital image correlation was also utilized to investigate the strain distribution and make the compressive fracture region clear, enabling the assessment of the fracture energy of ASR-degraded concrete. The results demonstrate that the stress-strain curve of post-peak stage of ASR-degraded concrete is influenced by the occurrence of cracks.

Several studies have demonstrated the reliability of the Stiffness Damage Test (SDT) (a mechanical test) and the Damage Rating Index (DRI) (a petrographic test) as diagnostic tools for ordinary concrete (aggregate particle sizes up to 20 mm) under free expansion. There is however limited information on the application of these tools to mass concrete mixtures incorporating large coarse aggregate particles and subjected to several stress states.This paper presents the findings of a study aimed at evaluating the use of these tools for mass concrete with reactive coarse aggregate particle sizes ranging from 5 to 40 mm. The SDT and DRI tests were performed on concrete specimens subjected to different stress states (with or without sustained load and/or passive confinement) at 100% R.H. In total, six stress states were studied ranging from free expansion to triaxial stress states. The SDT results obtained were found to be highly sensitive to the stress states to which the specimens were subjected, depending on the resulting cracking pattern. In contrast, the DRI results can capture the damage state of the specimens, irrespective of the stress states and specimen orientation.

The influence of crack orientation in concrete due to the alkali–silica reaction (ASR) under restraint conditions on the change in compressive behavior is numerically evaluated. In the analysis, aggregates and mortar are modeled separately using a 3D rigid-body spring model. The mechanism of generating expansion pressure inside aggregates is described using the expansion model. ASR expansion under various restraint directions is simulated to reproduce the crack orientation due to ASR and then uniaxial compressive loading is performed. It is observed that crack orientation is parallel to the restraint direction and also affected the compressive behavior. Expansion cracks perpendicular to the loading axis caused a large reduction in compressive strength and elastic modulus. Furthermore, the stress distribution in a cross section during loading indicates that cracks parallel to the loading axis do not strongly affect compressive stress transfer, whereas perpendicular cracks prevent compressive stress transfer.

This study addresses the crucial issue of determining the tensile strength in alkali-silica reaction (ASR)-damaged concrete slabs and shells without shear reinforcement. By studying the underlying theories and assumptions inherent in recognized test methods, augmented by new experiments and insights from the literature, this investigation delves into the limitations and applicability of each method to ASR-damaged concrete.Uniaxial tensile testing is found to be overly sensitive to local weaknesses, leading to significant underestimations in ASR-damaged concrete. Brazilian split testing is shown to evaluate compressive strength in ASR-damaged elements rather than tensile strength. Due to the necessity for large specimens, Flexural testing is unsuitable for concrete with low tensile strength and is deemed impractical for existing structures. In contrast, the failure modes observed in wedge splitting for ASR-damaged concrete closely resemble the considered mechanism in the fracture mechanical model used for determining tensile strength based on wedge splitting results. Consequently, wedge splitting is identified as a suitable method for assessing the tensile strength of concrete from ASR-damaged slabs or shells without shear reinforcement.

This study aims to investigate the relationship between mechanical property degradation and expansion through quantitative crack morphology analysis in ASR-affected concrete. Three groups of specimens with different reactive aggregate sizes were prepared and subjected to the alkali-silica reaction (ASR) acceleration. The expansion of each specimen was continuously measured, and tests were conducted to observe the compression behavior and crack patterns exhibited by the specimens at different levels of expansion. The specimens were sliced and subsequently embedded into fluorescent resin, and crack images were captured using a digital camera under ultraviolet light. Image analysis techniques were employed to obtain quantitative information regarding the crack size, including length and width distributions. The experimental results revealed that larger cracks resulted in a higher compressive strength reduction than smaller cracks. Furthermore, we demonstrated that there is a strong correlation between the compressive strength and expansion when considering the crack size distribution. This research paves the way for future models to better predict the mechanical behavior of concrete structures under ASR deterioration.

Crack patterns affect the stress-transfer mechanism and thus have a significant impact on the structural performance of reinforced concrete (RC) members. The alkali-silica reaction (ASR) induces various crack patterns in concrete depending on the environment and confinement conditions, which makes it difficult to predict the structural performance of ASR-induced RC members. According to previous structural tests on ASR-damaged RC members conducted in Japan, localized cracks along the longitudinal reinforcing bars reduced the shear capacity of the RC members, whereas dispersed microcracks increased it, leading to ductile flexural behavior. The authors’ research team developed a mechanical behavior model for ASR-affected concrete in which the resistance of the ASR gel filling the cracks and crack patterns are considered. This study aims to analytically investigate the structural behaviors of RC members with different ASR crack patterns based on a mechanical model. RC members with localized cracks and dispersive microcrack patterns were simulated, and the analysis results showed distinctly different behaviors for the two crack patterns. In the RC members with microcrack patterns, stress was effectively transferred and the gel resistance increased, which significantly improved the shear capacity and ductility. However, in localized crack patterns with a large crack, the gel hardly resisted the stresses in the cracks, and the shear crack propagated more easily, leading to a reduction in the shear capacity. In addition, by comparing the analysis and test results, the analytical model accurately reproduced the shear capacity reduction of ASR-damaged RC members owing to localized cracks.

High-voltage electricity pylons are anchored in concrete foundations, which are mainly subjected to pull-out and compression loads. Under these loads, concrete aging and pathologies can lead to mechanical stability issue, and even failure. The alkali-silica reaction is a possible pathology that can be encountered in this type of structure. The aim of this work is to propose a method to analyze the mechanical behavior of the foundation affected by ASR under pylon pull-out. ASR is introduced, and an experimental protocol is proposed to create it in the mortar. A pylon pull-out test from a small-scale mortar foundation is carried out directly in an X-ray tomograph. This so-called in-situ test, coupled with computed tomography (CT), enables the force-displacement curve and failure modes to be analyzed. The test has already been carried out on sound mortar and will be extended to mortar affected by ASR. It will then be possible to deduce the influence of ASR on foundation failure modes.

Global warming is expected to increase average temperatures in South Africa by up to 3 ℃ by 2050, compared to 1961–2000. This increase in temperature will change the environmental loading on arch dams, which are sensitive to closure temperature. In addition, the rate of concrete swelling due to chemical reactions such as aggregate alkali reaction (AAR) is expected to increase. This paper presents the results of a study of the impact of climate change on two double curvature arch dams in South Africa. One of the dams is subject to concrete swelling due to AAR. The subject dam is Kouga Dam located on Kouga River in the Eastern Cape Province of South Africa. The dam has been subjected to AAR since the early 1970s. The study showed that long-term temperature increase will induce permanent upstream displacements leading to an increase in tensile stresses on the dam wall. In addition, increased temperature will accelerate the swelling of dams due to chemical reactions, further increasing both tensile and compressive stresses in the dam wall. These effects, in combination with the hydrostatic load, may lead to cracking of the dam wall in critical locations.

Aggregate interlock is a critical shear resistance mechanism for the shear design of reinforced concrete structures. This mechanism relies upon shear transfer through cracks and depends on the bearing and the friction between aggregates and cement paste. The effectiveness of aggregate interlock mechanism is affected by the resistance of the cement paste and aggregates, as well as the crack opening and the structural restraints (e.g., presence of steel reinforcement and supports). The effect of alkali-silica reaction (ASR) on aggregate interlock is a complex phenomenon that impacts aggregate interlock. On the one hand, ASR may cause distress within the aggregates and reduces bond and friction between aggregate and the cement paste, reducing aggregate interlock capacity. On the other hand, enhanced confinement and compressive stress transferred across the crack interface caused by structural restraints and ASR concrete expansion may increase aggregate interlock capacity. To adequately consider these controlling and competing mechanisms, this paper examines the shear friction behaviour measured by push off tests and carried out on ASR affected concrete specimens (ASR-induced expansion up to about 0.12%). Results are compared with the predictions of various existing analytical models including those in design codes fib-model code 2010, ACI-318 and CSA A23.3.

Alkali-silica reaction (ASR) reduces the serviceability of affected structures, and temperature significantly enhances the development of the deterioration mechanism. The assessment of the role of temperature in the reaction is however incomplete without the evaluation of induced internal damage. Although the Damage Rating Index (DRI) has proven to be a reliable tool for assessing internal damage in ASR-affected concrete, its applicability over a range of exposed temperatures has not been explored. This study exposed 36 concrete cylinders containing a highly reactive aggregate to three storage temperatures (21 ℃, 38 ℃, and 60 ℃) and 100% relative humidity. The kinetics was monitored over time, and ASR-induced inner damage was evaluated using an extended version of the DRI. Results show that the petrographic features of ASR-affected concrete are significantly influenced by the exposed temperature, even at similar expansion levels. Moreover, an increase in temperature induced a difference in microstructural properties, such as crack width, length and density.

Over the recent decades, numerous research projects were developed to better understand the alkali-silica reaction (ASR) development as a function of time, especially the formation of reaction products and its association with induced deterioration. Several imaging techniques were used in this regard, such as scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). Although SEM/EDS has been ever since well recognized as a powerful tool to detect the presence and to characterize the morphology and composition of ASR-products in concrete, the appraisal of ASR-induced damage development and degree via SEM alone is not fully possible, because of the intrinsically altering nature of the respective specimen preparation. This work aims at appraising ASR-induced products formation and the associated deterioration through a coupled SEM/EDS and X-ray micro-tomography (XMT) analysis. Concrete mixtures incorporating a highly reactive fine aggregate were fabricated and stored in conditions enabling ASR development. At 3–4, 11, 16, and 24 weeks, the samples were prepared and tested with the three techniques. Preliminary evaluations show quite promising results in terms of ASR-secondary products formation and composition along with cracks generation and propagation. Further quantitative analysis will help to fully describe ASR-induced deterioration mechanisms triggered by highly reactive fine aggregates.

Delayed ettringite formation (DEF) and alkali silica reaction (ASR) negatively affect the mechanical properties of concrete. This work investigated the compressive strength and dynamic elastic modulus variations of concrete to restrain the expansion progress owing to the internal swelling reaction (ISR) mechanisms (i.e., ASR and DEF). Two concrete mixtures are used to induce the damage in concrete cylinders owing to DEF and the combined effects of ASR and DEF. The expansion and dynamic elastic modulus of the free specimens (without restraints) are measured periodically during the storage period. The compressive strength and dynamic elastic modulus of restrained concrete cylinders are higher than the free specimens which have relatively lower expansion. The higher mechanical properties then gradually reduced with an increase of expansion but remained higher than that of specimens allowing free expansion.

The aim of this study is to investigate the cracking anisotropy and mechanical performance of alkali-silica reaction (ASR)-expanded concrete under multiaxial restraint conditions. Uniaxially and biaxially restrained specimens were prepared using a newly fabricated fixture, and ASR expansion acceleration and compression tests were performed. Expansion and cracking anisotropy were observed for different restraint conditions. In addition, a decreasing tendency in the mechanical performance was observed in the subsequent compression test when the specimens were loaded in the direction perpendicular to the cracks. The remaining mechanical properties were significantly related to the expansion parallel to the loading direction. Next, the quantitative extraction of crack characteristics on the cut surface was attempted using an image detection technique. Each crack was isolated, and its angle was calculated. The trend of the reduced mechanical performance was summarized using information on the angle of cracks in the cross-section. By using the crack information extracted via image detection analysis, a more quantitative prediction of the mechanical performance of ASR-expanded concrete can be achieved.

Understanding the expansion of Alkali-Silica Reaction (ASR) under restraint and its impact on the mechanical properties of concrete is crucial for evaluating and predicting the performances of concrete structures damaged by ASR. Nowadays, ASR damage has even been observed in prestressed concrete structures, which are considered highly durable. Evaluating their performance, particularly in terms of structural safety, necessitates consideration of both active and passive restraint influences. This study aims to investigate the effects of prestress on the expansive behavior of concrete due to ASR and to discuss this behavior under both active and passive restraint conditions. The focus of this research is post-tensioned prestressed concrete at low-stress levels. Experimental results indicate that concrete expansion along the restraint direction is dependent on the restraint rate, expressed by both prestress and steel bar. Moreover, expansion perpendicular to the prestress direction is greater than stress-free expansion. These findings result in nearly identical volumetric expansion in different restraint conditions. Furthermore, the study delves into the degradation of the modulus of elasticity under restraint and considerations in the assessment of real structures.

In the context of massive concrete structure ageing, such as nuclear power plant containments or hydroelectric dams, the study of cementitious material durability is of great interest. In particular, the Alkali-Silica Reaction (ASR) can drastically reduce the durability of such structures. A reactive transport model (species transport and chemical reaction) of ASR able to simulate the progressive aggregate dissolution, the silica gel precipitation and its localization depending on the aggregate characteristics (chemical composition, diffusion properties, size, and morphology) is proposed. The objective is to consider mainly physical measurable parameters and thermodynamic constants. The ion transport is given by Fick's second law of diffusion and the geochemical system models the aqueous complexation and solid reactions. The thermodynamic equilibrium of chemical processes is assumed, except for the dissolution of the reactive silica, that is modeled by a kinetic reaction. Two main reaction products of ASR are considered, a low Ca/Si ratio C-S-H and an expansive alkali-silica gel. The application focuses on the cement paste and aggregate interaction. The results fit well with the experimental observations where the ASR gel forms inside the aggregate particle and the C-S-H precipitates at the interface between paste and the particle. The effect of aggregate composition and particle size on the overall ASR kinetic and gel precipitated localization is investigated.

Modeling damage generated by distress mechanisms like alkali-silica reaction (ASR) in plain and reinforced concrete structures is very complex, yet necessary to correctly assess the current (diagnosis) and future structural response (prognosis) of affected concrete members. In this context, the macroscopic ASR model developed by Gorga et al. (2018, 2020) was implemented. The macro-scale modeling approach accounts for the most important parameters affecting ASR through an engineering approach, without the need for non-technical guesses or to “fit” model parameters. The proposed approach has already been used to assess an ASR-affected dam and will be further validated by simulating a structure with more detailed monitoring data, the Bemposta dam in Portugal. The dam structure is described in detail, results of previous analyses performed by LNEC are described, modeling approaches are compared, and a description of the work currently being developed is presented.

Despite the importance of the assessment and prediction of structures affected by internal swelling reactions (ISR), robust methodologies have not yet been established. ISR damage of structures occurs through microscopic damaging of the materials due to various chemical reactions and the formation of damaged microstructures, leading to macroscopic stress/strain variations in the structure. Therefore, understanding the relationship between the microscopic and macroscopic aspects is key to refining the performance assessment of structures affected by ISR. To address these issues, a technical committee, TC211A “Technical Committee on Assessment and Prediction of Expansion due to Internal Swelling Reactions in Concrete Structures”, was established and active in 2021–2023 in the Japan Concrete Institute. This committee mainly discussed the ideal direction of test methods and models for assessing the performance ISR-affected structures, with the aim of presenting a more effective and feasible ISR risk-assessment method. In this paper, the outcomes of TC211A are presented.

In this study, for investigating the factors affecting expansion transfer in aggregates in concrete, a numerical analysis was conducted to precisely evaluate the crack propagation from different expansive sites under applied stress. A 3D rigid body spring model (RBSM) was developed for a single aggregate particle, representing spherical aggregates. The model simulated the expansive site distribution in the aggregate. Therefore, the model could analyze the expansion behavior and crack propagation in concrete under constraint conditions. Numerical analysis results indicated that in the gel pocket model, which assumes a heterogeneous aggregate, crack generation was significantly suppressed under constraint stress. This is because the orientation of crack propagation is decided by the mesh geometry of the Voronoi element of the aggregate, and it is difficult to change the orientation of crack propagation. On the other hand, the orientation of crack propagation in the reaction rim model, where the expansive sites were uniformly formed at the aggregate surface layer, could be easily changed under constraint stress.

Delayed ettringite formation (DEF) is a pathology of concrete that permanently affects many massive civil engineering structures such as bridges, dams or nuclear power plants. Realistic numerical modelling of the behaviour of these structures is necessary to establish their safety and optimise their maintenance. At present, few numerical models are able to faithfully reproduce the structural behaviour of DEF at this scale because of the diversity of phenomena to be considered. Temperature, water saturation and amount of alkali act directly on the chemical balances involved. In addition, the correct evaluation of the pressure generated by DEF, creep and induced cracking is also essential.In this work, a thermo-hydro-chemo-mechanical model is applied to the aging phase of three laboratory beams from the bibliography with different reinforcement rates subjected to controlled young age heating.The methodology used in this paper is composed of two steps to calibrate and validate the calculations. The calibration phase is carried out on a sample, on the deflections of the beams and on the cracking pattern of the unreinforced beam, then, the validation is carried out on the chemical advancement obtained by coring, the other displacements and cracks on all the beams as well as on the stresses in the reinforcements.The model correctly reproduces the experimental measurements carried out on these beams attesting to the correct evaluation of the main phenomena involved. However, sensitivity to water and alkaline leaching is important. Multiphysics calibration is therefore necessary to obtain satisfactory results in terms of displacement, stress and cracking. For a predictive calculation of a structure, a parametric study also seems necessary.

Expansions due to alkali-silica reaction (ASR) cause damage in civil engineering structures such as dams, bridges, pavements. A lot of work has been done to have a better understanding of the ASR mechanisms, both in the laboratory and in the field. The aim of this paper is to perform the forensic analysis of a concrete pavement located in Bécancour area (Québec) to understand its failure. This mechanical analysis is based on recent knowledges in terms of material and structural modelling of ASR. The data necessary to evaluate the mechanical behavior of structures damaged by ASR are first described (temperature, humidity, concrete delayed deformation, expansion potential). Modelling parameters are calibrated on expansion measured in the laboratory and used to predict expansion in outdoor conditions. The structural analysis of the pavement shows the importance of the combination of ASR expansion with cyclic thermal loading. Once the pavement joints are filled, due to ASR swelling, concrete dilatation induces important compressive stresses in summer. Such stress can lead to concrete damage and increases the risk of pavement buckling. This work emphasizes the importance of taking account of the combination between the different loadings (mechanical and environmental) and expansion in the mechanical analysis of structures damaged by ASR. It gives interesting teachings concerning concrete pavements but also other thin structures affected by such expansive mechanisms.

Re-assessment of structures affected by internal swelling reactions (ISR) such as alkali-silica reaction (ASR) or delayed ettringite formation (DEF) often requires the use of numerical models to simulate concrete expansive behavior with more or less sophisticated constitutive equations. In the case of real structures, for which few information is available, applying these tools would imply expensive and time-consuming in-situ examination and laboratory analysis in order to achieve a direct identification of model parameters. However, these real structures are usually subjected to monitoring policy, which implies that a large number of reports of apparent disorders (cracks, deformation, etc.) are available.This communication takes place in a project aimed at developing numerical techniques to identify parameters of a model representing ISR-affected concrete based on information provided by the sole visual inspection of the structure surface. Due to its high complexity, this identification problem is first treated on simplified structural elements.This communication will focus on a series of numerical examples representing the prism of plain concrete and reinforced concrete, affected by ASR or DEF and submitted to various conditions of temperature (constant or varying with time), moisture (uniform, spatial heterogeneity, variation with time due to drying…) and stress (no stress, uni-axial stress, multi-axial stress). Then, numerical indicators representing surface degradation will be presented. Finally, the relationship between these indicators and the different parameters of the ISR-affected concrete model will be analyzed. This analysis is the first step to achieving a methodology for identifying these parameters.

In France, the extending of nuclear power plant service life from 40 to 60 years is an actual issue. Due to the number of nonlinear and concomitant concrete phenomena, such structure needs a reliable tool to ensure and predict their behavioural evolution. In this work, a thermo-hydro-chemo-mechanical model considering passive reinforcements in a distributed manner is applied to the calculation of a containment vessel with ISR. Shrinkage, creep, ISR swelling and induced damage are strongly coupled to each other, and all depend on thermal and humidity environmental conditions. The calculation is based on the available basic mechanical characteristics, the passive reinforcement ratios, the tensioning kinetic data of the prestressing cables and the structure’s geometry. The results show a good correlation with the multiaxial strains of the structure on the in-situ data. The model is used to make predictions over the next 30 years. Two scenarios of maximum swelling are considered. Cracking, which is an essential information for these containment structures, is compared between 30 years and 60 years. The prediction at 60 years shows that the pathology, with a hypothesis of rapid evolution, does not have a deleterious effect on the structure.

In prestressed sleepers used in India, longitudinally extending and map-shaped cracks occurred at many service points 6–9 years after manufacture. Polarizing microscopy and electron microscopy of thin sections made from the concrete showed that the gneissic aggregate had a distinct ASR. Other gaps at the aggregate-cement paste interface and reticulated cracks, which were different from the extension of the ASR cracks, were also observed. The filling of ettringite within the gaps and cracks confirmed that DEF had occurred. It was therefore concluded that the cause of deterioration of the Indian sleepers was combined ASR and DEF deterioration. The very high alkali content of the cement used in India, coupled with the hot and humid environment, may have contributed to the development of ASR and DEF. In addition, an estimation of whether ASR or DEF occurred prior to the ASR or DEF was made from microscopic texture observations. The results showed that both were considered to have occurred prior to each other.

This paper summarizes an important R&D industry-university collaboration project related to a hydro-electric facility affected by alkali-silica reaction (ASR). The work in progress started almost ten years ago and aims to predict the long-term behavior of the facility using advanced finite element method (FEM).After a presentation of the facility, extensive experimental investigation campaigns on concrete cores extracted from the dam and on specimens made from concrete mixtures similar in composition and constituents to the ones used for construction will be detailed. Three laboratories were involved in the characterization campaigns. At Hydro-Quebec (HQ) research institute (IREQ), basic concrete testing, expansion and long-term creep tests were performed. At Polytechnique Montreal, large concrete blocks were tested using wedge splitting tests to assess the impact of ASR on the concrete fracture energy (size independent), a fundamental input parameter for numerical modelling of mass concrete structures. At Laval University, the focus was on characterizing the kinetics of the reaction, the anisotropy effects from casting or coring direction and the effect of confinement upon expansion.The paper presents the results from an owner’s strategic perspective and discusses how they will be applied to the management of the dam. More advanced technical and scientific aspects are detailed in other papers presented at ICAAR 2024.

Alkali-silica reaction (ASR) is among the most harmful deterioration mechanisms affecting concrete infrastructure worldwide, impacting more than 50 countries. Over the last decades, different laboratory tests have been developed to assess and forecast ASR-affected infrastructures for new structures. Meanwhile, laboratory techniques have evolved for reliably assessing deterioration mechanisms of existing structures in their cause and extent (diagnosis). There are, however, questions regarding a consistent protocol for prognosing ASR-affected structures, particularly in incorporating laboratory results to predict the remaining service life. In this context, this study examined different residual expansion (RE) methods within a forecasting protocol. While results showed variations in laboratory-induced expansion, extrapolations to field conditions resulted in similar ASR expansion rates. However, the reliability of these projections, crucial for accurate forecasting of ASR-affected structures, requires further validation through experimental studies and field observations.

The single-curvature arch dam with a maximum structural height of approx. 25 m was constructed in the early 1920’s and deterioration was observed shortly after. The cause of deterioration was assessed to be concrete growth in the 1950’s and alkali-silica reaction as root cause was confirmed in the 1960’s.Several condition assessments were carried out since deterioration begun that confirmed ongoing deterioration due to ASR which led to the asset owner’s decision to plan the replacement of the dam in the near future. To assess the current structural integrity and predict the residual life of the structure a detailed investigation was carried to assess the physical concrete properties, rate of deterioration and to determine potential failure modes.The physical concrete properties did not appear to have deteriorated over the last 30 years despite ongoing confirmed horizontal and vertical displacement which has increased leakage resulting in an accelerated rate of freeze-thaw attack. The numerical model identified the dam to be stable but hinges had already formed requiring the development of a repair strategy to address potential structural risks until replacement of the structure and to potentially reduce the rate of deterioration.This paper presents the development of the physical concrete properties over time, parameters to be used in and results of the structural analysis, future structural behaviour and a review of potential repair strategies.

Many dam owners around the world have been faced with swelling concrete issues at their dams and hydro projects for the past 70 years or more. Several different management strategies have been adopted, although the options appear limited and no “once and forever” fixes have been developed. In some cases alkali-silica reactions (ASR) and associated expansion appear to have diminished after 30 or so years, while in many other cases it continues with more or less vigor.In cases where the ASR continues, given the very long required service life of dams, a hundred years and more, there is a clear need to seek to identify some practical solutions to limit the ASR and its effects in these long-term cases. In such cases the potential role of releasable alkalis from aggregates and recycling needs to be clearly understood to be able to reliably forecast future behavior and develop a long-term management plan. The role of water and humidity must also be understood.The control options are limited but given the long timescale, and often the slow rate of expansion, some very long-term solutions, such as drying the concrete to reduce the expansion rates in some parts of dams and associated structures, may be possible and worth considering in some cases. This paper examines some of the issues involved in such notions and identifies issues that would need to be addressed to determine their feasibility and practicability.

Fontana Dam is TVA’s largest concrete dam and the largest dam east of the Mississippi river in the United States. The dam is a multipurpose project that provides hydropower, flood control, recreational, and water supply benefits. Most discharges from the dam pass through the powerhouse. The dam also has a low-level outlet and a gated spillway which serves as the primary lake level control during floods.The dam was constructed during the Second World War and has a history with Alkali Aggregate Reactivity (AAR) concrete issues that date back to the early 70s. Until recently, AAR issues had been manifested at the spillway by gate binding issues that precipitated slot cuts and annual full travel inspections of the gates.During a routine full travel inspection in late 2017, a crack was observed on an exposed steel trunnion assembly that supports the spillway gates. Immediately repairs were made to the trunnion assembly to restore it to original design condition.This paper will describe the investigations into the cause of the cracking, and an update on the current condition and monitoring program. An analysis of AAR effects on the gate anchorage is also presented. As this trunnion assembly and gate anchorage design is similar to that used at numerous other concrete dams, the results of this study might be instructive to other dam owners who may have concrete affected by AAR.

In the last decades, a significant number of large concrete infrastructures with deterioration problems related to alkali-silica reaction and delayed ettringite formation have been identified worldwide. Currently, due to phenomenological and assessment complexities it is still difficult to provide recommendations for the prevention of ASR damage in new structures, involving certain aggregates, as well as to perform a complete assessment of the actual condition of an affected structure and an accurate prediction of its future deterioration. This paper aims to contribute to the ongoing discussion of this topic and, therefore, presents some of the work performed on diagnosis and prognosis of internal swelling reactions in the concrete from the Cahora Bassa dam, in Mozambique. The Cahora Bassa dam, built between 1972 and 1975, is a part of a hydroelectric scheme located on the Zambezi River. This paper includes a very brief overview of the information available on the concrete and its constituents, at the time the dam was built, and succinctly presents the analysis of some of the results obtained in the laboratory test campaign (namely, microstructural analyses, chemical analyses, and expansion tests) performed on concrete cores extracted from the structure, in 2017, and on the aggregate used in the dam’s concrete.

This paper presents an updating of the analysis and interpretation of the structural behavior of Covão do Meio dam (in Portugal) which concrete is affected by an ongoing swelling process.The simulation of dam’s behavior over time is based on mathematical modelling, considering a three-dimensional representation of the structure and of its rock mass foundation, solved by the finite element method. All relevant actions are considered, namely the dead weight of the materials, the hydrostatic pressure on the upstream face, the temperature changes in the dam’s body and the concrete expansions of internal origin. The computing of the swelling action considers the influence of the temperature and of the stress fields. The structural model considers the concrete viscoelastic behavior and the cracking phenomena.The main monitoring quantities and the corresponding numerical results, including the cracking patterns, show a good agreement, attesting the adequacy of the models used to simulate dam’s behavior over time.

In 2006, Cofiroute, a French highway concessionaire, discovered that a series of 25 bridges with precast prestressed girders were affected by the pathology of delayed ettringite formation in concrete. Faced with this still poorly understood phenomenon, Cofiroute surrounded itself with scientists and carried out multiple monitoring and diagnostic studies.After a brief presentation of the 25 bridges, the article presents the results and the learnings drawn from these actions with regard to the evaluation of the evolution of the cracking through cracking index measured during several years, the evaluation of the swelling potentials through residual expansion tests on several tens of concrete cores, the evaluation of the effects of the pathology on the structures by means of numerical modeling (thermal, hydric, thermodynamic, mechanical) and reassessment. The article presents the methodology adopted to approach a classification of the current state of 200 of the 848 beams correlated to their probable evolution, with the objective of defining methods and priorities of treatment. In addition, are presented the experiments of treatment by water protection carried out on some of them. The article discusses the difficulties encountered during these various operations and in particular the “lack” of data/information, recognized as relevant, on the concrete at a young age (cement data, curing temperatures, concrete temperature curves, etc.), the assumptions considered to model the effects of the reaction on the characteristics of the concrete in order to appreciate their degraded functioning, the evaluation of the sensitivity to the water influx, and the evaluation of the performances and the efficiency of the solutions of protection by impermeable coatings.

Alkali aggregate reaction (AAR) is one of the most harmful damage mechanisms affecting concrete infrastructure worldwide. Several numerical models have been developed in the past to appraise the expansion attained to date due to AAR and to predict its potential to generate further damage on affected infrastructure. Gorga et al. (2018) proposed a new finite element approach to assess AAR-affected structures accounting for both the most important microscopic and macroscopic aspects affecting the chemical reaction. The most distinct characteristic of this methodology is that it does not oversimplify nor overcomplicate the analysis of the reaction, while still being capable of accurately representing the anisotropic expansion and its macroscopic consequences. Slender structures have already been successfully simulated using this approach. However, it has been found that AAR-affected slender and massive structures do not necessarily behave equally, which is mostly due to the lack (or very little amount) of leaching and the potential alkali release from aggregates at later stages of the reaction on massive structures. This paper presents the validation analyses and simulations performed on an ASR-affected dam in Brazil (Paulo Afonso IV) in order to appraise the accuracy of the prior proposed approach for massive structures.

Some dams in the EDF parc exhibit irreversible displacements that can be attributed to internal swelling reactions. To evaluate the impact of this swelling, numerical models are implemented. These models allow for the reproduction of displacement evolution, estimation of stress levels, and prediction of long-term cracking. Calibration of these models involves the use of data obtained from monitoring and laboratory tests, which necessitates the formulation of certain assumptions, such as the areas prone to swelling and the magnitude of swelling.However, formulating these assumptions can be challenging due to the numerous parameters involved in chemical reactions. Factors such as the presence of water, temperature, concrete composition, and the temperature reached during concrete casting play a crucial role in these chemical reactions, and these influential factors are not always well-known within the structure. Additionally, parameters like creep and cracking directly impact the response of the modeled structure to external loading. All these factors influence the model's response and can lead to erroneous assumptions, resulting in an imperfect diagnosis of the structure, either by overestimating swelling in certain areas of the structure or by not considering it at all.To improve the validity of the assumptions made, one approach is to measure stress levels in situ and install sensors for continuous monitoring of the structure. These long-term measurements and observations allow for the validation or modification of the initial diagnosis, accordingly, ensuring better alignment with the actual behavior of the structure.This paper provides an example where stress measurements have enabled improved modelling.

Monitoring concrete structures is a customary practice by hydropower companies during the service life of construction projects. Constructed in the 1970s, structures from a Hydroelectric Power Plant (HPP) in Brazil were diagnosed in the past with alkali-silica reaction (ASR) solely due to map cracking and little laboratory analyses and tests. In the meantime, further assessments on concrete structures. Larger data from instrumentation, and more detailed experimental program with concrete cores drilled in field followed by mechanical and stiffness tests and microstructural analyses pointed to the presence of secondary ettringite in the concrete samples, besides ASR gel. Deterioration indexes and microstructural aspects signaled that those concretes suffered from coupled attack, with DEF and ASR occurring simultaneously. This paper aims to present the main results from more recent investigations that elucidated this new diagnosis of deterioration and the different behavior of elements according to its structure in the field.

The scope, results, and experience from the Norwegian research project MESLA (Management and Extension of Service Life of infrastructures affected by Alkali-silica reactions (ASR) are presented. The main objective of the project is to contribute to an improved system for management of our infrastructure. A major task for the project is to evaluate the effect of compressive stress on the expansion and cracking, creating large degrees of anisotropy. The project has access to many bridges for field survey, monitoring and sampling for laboratory investigations. Based on condition data, structural analyses are carried out for selected bridges, and material models for ASR-affected concrete are developed. One of the monumental bridges considered is the Tromsø bridge (1960), where the ASR-induced expansion and deterioration is leading to closed expansion joints, extensive cracking, column deformations and damaged bearings. The material degradation and the expansion induced moments are of vital importance, and relevant deteriorated structural members are the bridge slab, continuous RC beams, post-tensioned beams and slender columns. The material degradation is mainly mapped by applying the Stiffness Damage Test method (SDT). Despite the ASR-induced damages, the Tromsø bridge has sufficient safety margin against structural failure, even though the need for maintenance is large.

As part of the Norwegian research project MESLA (Management and Extension of Service Life of infrastructures affected by Alkali-silica reactions (ASR)), three case studies are presented to illustrate various aspects of ASR deterioration in bridges: (1) Damaged bearings and support structures, (2) material degradation, (3) additional moments and their consequences. The three included bridges are a long bridge consisting of a suspension bridge and two reinforced concrete viaducts, a railway bridge which is a steel truss girder supported by slender reinforced concrete piers, and a 200 m culturally protected beam bridge.

In this research a concrete dual carriageway in the province of Buenos Aires (Argentina) was studied. The section analyzed joins a street in Bahía Blanca city with provincial and national routes. The pavement is 0.22 m thick and was built over a cement-soil base 0.15 m thick lying over a 0.20 m thick hardpan. The fine aggregates used correspond to sands from the south of the province of Buenos Aires qualified as reactive in laboratory tests and in some structures in service. The coarse aggregate is a non-reactive crushed granitic rock. The structure shows signs of deterioration that could be associated to the alkali-silica reaction (i.e. stains, map cracks, white products associated with fissures, etc.). In order to verify the occurrence of the ASR and to evaluate the actual condition of the concrete different physical-mechanical and microstructural studies were performed on cores extracted of the structure. Density, absorption, volume of voids, carbonation depth and compressive strength were determined. In addition, Stiffness Damage Test and Damage Rating Index were implemented coupled with polarizing microscopy and scanning electron microscopy.

Alkali-silica reaction (ASR) and internal sulfate attack (ISA) have compromised concrete sleepers both individually and combined. Although numerous studies have identified the cause, they have not effectively estimated the extent of the damage. This research assesses concrete sleepers of diverse ages using a multi-level assessment integrating microscopic and mechanical tools. The assessment encompassed visual inspection specifically focusing on crack openings normalized by a reference gauge, microscopic evaluations through the damage rating index (DRI), and mechanical tests, including the stiffness damage test (SDT) and compressive strength. The DRI revealed damage features associated with both aggregate particles and cement paste deriving from internal swelling reactions (ISR). Notably, the proportion of these features varied with the sleeper's age. Therefore, the multi-level approach proved effective in assessing the current condition of ISR-affected sleepers. Integrating this approach into regular inspections could potentially extend the lifespan of ISR-distressed sleepers.

Alkali-carbonate reaction (ACR) is an internal swelling reaction (ISR) rarely identified in the field. While ACR has been extensively studied in laboratory using known reactive aggregates, such as the one from Kingston, Ontario, the scarcity of field cases limits the understanding of ACR's behavior in critical infrastructure. This paper details a comprehensive condition assessment of concrete structural members affected by ACR bearing no secondary products. Affected sleepers with ten years in service in northern Brazil were multi-level assessed (i.e., microscopically and mechanically) and the chemical composition of the aggregate particles and the cement paste were determined by XRF and XRD. The results uncovered that aggregate chemical composition felt within the potentially expansive thresholds specified by CSA A23.1-14/A23.2-14 for ACR and calcite and brucite are present in the system. The multi-level assessment outcomes further reinforce the hypothesis of ACR with a low damage level. In conclusion, this group of sleepers is likely affected by ACR much less aggressively than previously observed in concrete members incorporating Kingston aggregate.

Typical mosaic-shaped cracks have been frequently identified mainly in concrete foundation blocks of some railway bridges built around 1970´s in South-eastern Brazil. These damages are attributed to the Alkali-Aggregate Reaction (AAR) and to the Delayed Ettringite Formation (DEF - Delayed Ettringite Formation). In view of maintaining the bridges in service, it was necessary to carry out a thorough evaluation of the evolution of the process that is destroying the concrete elements, with the aim of looking for indicators that can be monitored for this purpose.All these studies gave rise to a management plan, which strategy is to intervene annually in a greater number of bridges that present damage with the challenge of seeking technically viable solutions, enabling faster and less costly interventions, and still mitigating the risks regarding structural and durability problems in these elements. For this purpose, additional test procedures have been accomplished with the concrete extracted from the bridges, like the Damage Rating Index (DRI), the Stiffness Damage Test (SDT), and in the field, the cracking index (CI) has been applied. These test procedures have been developed to assess the current condition and the potential for further expansion/distress of chemical-affected concrete.From the test results and the damage identified during bridge inspection, assets will be selected to intensify monitoring or carry out interventions, based on the risk of each bridge determined in the Bridge Management System (BMS). A procedure for ranking bridges for maintenance is proposed to define prioritization and actions to be adopted in each case.

The 043-FA concrete bridge in Brazil was built using aggregates susceptible to alkali-silica reactive (ASR), exposed to conditions enabling the development of delayed ettringite formation (DEF) and is still in service. Over the years, many signs of deterioration developed on various structural elements of the bridge, mostly in the foundation blocks and concrete columns. As such, cores were extracted from the structural concrete elements following in-situ inspections. Therefore, this work presents results from the multi-level condition assessment using the damage rating index (DRI) and the stiffness damage test (SDT) to determine the cause and extent of the damage to the concrete due to ASR coupled with DEF. Consequently, elements show a moderate degree of damage (i.e., 0.10–0.15% expansion) except for one foundation block (i.e., B02 at 0.25–0.30% expansion), which displayed an advanced damage level, thus indicating the bridge’s non-conformity to Brazilian safety protocols.

The degradation of the Foz do Dão bridge, that served the IP3 road and is located over the Aguieira dam reservoir, in Portugal, mainly due to the internal swelling reactions in concrete, resulting in visible cracking in its piers, led to the bridge replacement in August 2015. Since 2009, this bridge has been subject to several inspections, including underwater inspections, laboratory tests of cores, as well as periodic geometric levelling of the deck and ambient vibration tests. These actions were aimed to characterize its structural behaviour and to detect damage growth that might jeopardize safety.The aim of this work is to characterize and interpret the structural behaviour of the highest pier. For this purpose, a three-dimensional numerical model, which considers the environmental conditions and the time-dependent behaviour of the concrete, was developed. The loads applied to the pier are the dead-weight of pier and the weight of the bridge deck, the pressure of the reservoir water, the effects of the thermal variations and of the swelling. The computing of the expansions considers the influence of the temperature and of the confining effect of the rebars and of the stress fields. The temperature variations at the pier were computed using a thermal model. The model was calibrated considering data obtained by laboratory tests, on samples extracted from the bridge and by the deck levelling.

A French highway manager, decided to launch a broad operation in order to detect bridges likely to be affected by DEF and to set up a policy of monitoring and management adapted to various situations. The first step of this operation consisted in identifying structures eligible for an adapted monitoring or immediate mitigation measures, and the challenge was to achieve this task without any specific investigations.A screening method was then developed, based on the information available in the structure files. Through this method, structural elements of the bridges were classified according to the probability of their being affected by DEF, to their visible degradation state and to how it could affect the global serviceability and security of the structure.This method has been applied to a set of 149 bridges. Then, the bridges have been classified amongst five different groups, for which different managing policies are proposed. Since it turned out that this screening method was not adapted to the foundation elements, a specific method was designed to discriminate them.In this communication, we will first describe the main features of the screening methods (the main one, and the one adapted to the foundations). Then, the results obtained for 149 bridges will be presented.

Serving as a critical link on the TransCanada Highway since the 1920s, this historic bridge provided an important connection over the Fraser Canyon in southwestern British Columbia for vehicle traffic until being taken out of service in the 1960s. Today it is regarded as a heritage structure and has, until recently, been a tourist attraction for hikers and other recreational users.Its concrete elements have, however, been affected by deterioration to variable extents. In this paper, we present some of the results regarding the effects of Alkali-Aggregate Reaction (AAR) and the role that it has played in the condition of the concrete. The methods used included site reconnaissance and inspection, core sampling, saw cut sampling, petrographic examination, compressive strength tests, and Damage Rating Index evaluations.These methods and data are presented and form the basis for an analysis of not only the new information gathered but also the limitations inherent to these approaches, as pertaining to this structure.

The footings of a bridge structure crossing the St. Lawrence River in Montreal were subjected to a diagnosis and prognosis study for ASR. The Damage Rating Index (DRI) and the Stiffness Damage Test (SDT) were used to evaluate the damage in the footings while the expansion tests on concrete cores (>95% R.H. at 38 ℃) and the water-soluble alkali content test were used to establish their expansion potential.Two types of concrete were identified in the footings. Even though both concretes showed extensive damage, higher damage was found in Concrete B with both the DRI and SDT results. Both concretes showed a similar (high) expansion potential even though a much higher water-soluble alkali content was measured in Concrete A. The lower damage and the higher water-soluble alkali content in Concrete A are due to the presence of a significant proportion of non-reactive volcanic rock type in the coarse aggregate. It is believed that an alkali-rich (feldspathoid) mineral in the volcanic rock type in the coarse aggregate of Concrete A has contributed to the high water-soluble alkali content measured on that concrete.

Alkali aggregate reaction (AAR) affected structures show reduced serviceability and premature distress in over 50 countries worldwide. Several approaches have been proposed to evaluate the reactivity potential of aggregates by varying the conditions known to trigger and sustain the reaction. Among them, the most popular methods are the accelerated mortar bar test (AMBT) and the concrete prism test (CPT). Nevertheless, exposed site data has increased considerably in recent years, showing significant discrepancies between laboratory results and actual concrete field performance. In this study, the variability of laboratory performance methods was explored indicating low and moderate accuracy in predicting field performance for AMBT and CPT, respectively. While it provides initial insights on the recalibration of the methods outcomes, advanced analysis methods are suggested to enhance such predictions. Therefore, such measures can enhance the safety of concrete infrastructures by accelerating the identification of risks associated with incorporating AAR-prone aggregates into new structures.

This paper presents the findings on the University of Texas at Austin outdoor exposure site after 20 years. The site was created in 2001 and is considered to be a warm weather site when compared to other outdoor exposure sites. The site contains exposure blocks subject to ASR and DEF. After 20 years, the exposure site contains more than 1000 exposure blocks and the data that has been collected has been used to update ASR standards, specifications, and guidance documents. This site contains materials from around the world including over 40 aggregates and at least 50 types of prevention measures. Findings from over the years have helped develop correlations between laboratory test methods and the field exposure blocks including a major concern that test methods such as the accelerated mortar bar test and the concrete prism test are not able to determine the replacement amounts of SCMs to prevent ASR in high alkali loading field exposure blocks. In addition, the site has shown that lithium nitrate does not prevent ASR in field blocks with high alkali loadings.

As laboratory studies of internal swelling reactions are usually performed on small-size samples, the results of these studies are not able to reproduce the real condition to which the massive concrete structures are submitted. The expansion data for two groups of specimens subject to aggregate-silica reaction (ASR) and delayed ettringite formation (DEF) are recalled in this study, including large mock-up blocks and core samples extracted from the block after 200 days of exposure. Each investigated case exposed the samples to the same conservation conditions. The objective of this study is (i) to analyze the experimental expansion data of laboratory specimens and large mock-ups exposed to ASR and DEF; (ii) to correlate the behaviour of real-scale massive structures with the residual expansion of core samples; and (iii) the final goal is to provide recommendations for predicting the long-term expansion of massive concrete structures based on residual strain analysis. The possible reasons for explaining the inconsistent expansion of specimens at multi-scales are proposed in this study, from the perspectives of differences in moisture degree, leaching degree of alkalis/calcium, temperature gradient, the occurrence of microcracks due to the high-speed action of the drill, and the restraint from the end support. The restraint effect induced by concrete self-weight and metal support is believed to be the main reason leading to the different behaviour of specimens at multi-scales. Calculations of the swelling stress and predictions of expansion are performed in this study, considering the restraint effect in constitutive equations that are coupled to a damage model.

Alkali-silica-reaction (ASR) exposure sites allow studying the behavior of concrete with reactive aggregates in natural exposure on the long term. As such, the exposed specimens can show both the kinetics and magnitude of concrete expansion and the effectiveness of ASR-suppressing measures. Moreover, the combination with accelerated laboratory tests makes it possible to validate the latter. Recently, two exposure sites have been established in Switzerland, one at low elevation in the Midlands and the other one in the Alps at an altitude of 2200 m above sea level. The goal of the present project is to validate the concrete prism test (CPT) and the residual expansion test (RET) used to assess the durability of a structural concrete. Concrete mix designs mirroring the current Swiss market for engineering structures and dam concrete are used. 40 concrete mixtures are produced in total. So far, the CPT has been conducted and the exposure of the cubes at the two sites for an intended duration of 15 years has started. After three years cores will be taken from selected cubes to perform the RET.

This paper reports on the performance of the Ontario Ministry of Transportation (MTO) Kingston Exposure Site (KES) experiment for ASR after 32 years. KES was constructed in 1991 for two main purposes: 1) to test the effectiveness of measures to control or mitigate ASR and 2) to compare results of short-term lab testing with long term field performance. The KES consists of concrete produced from six different concrete mixtures using various cements and supplementary cementing materials (SCMs) in combination with the Spratt Aggregate. The mixtures were cast into 13 beams 0.6 × 0.6 × 2 m (6 reinforced and 7 non-reinforced beams), and 6 sidewalk slabs 0.2 × 1.2 × 4 m. At 32 years, all but two mixtures are demonstrating unacceptable field expansions in the unreinforced beams. Comparison of the field expansions with laboratory test data for the same mixtures reveals that the concrete prism expansion test (CPT) tends to underpredict actual field expansion, and that the accelerated mortar bar test (AMBT) is likely a better predictor of the potential efficacy of selected mitigative measures for countering ASR. The raw data from KES has been released and is publicly available to the AAR research community for download through MTO’s Technical Publications website.

Established testing procedures for ASR risk of aggregates do not always reflect the actual reactions taking place in real life exposure sites. In this study the behavior and performance of three different aggregates used in Austrian highways was compared in standardized testing procedures (ÖNORM B 3100, 38 ℃) and non-standardized tests supported by data from 10 year old highways built with the aggregates. The testing showed that the aggregates were usually a lot less reactive in real life exposure settings than in standardized settings. The modification of parameters within the testing procedures (e.g. cement type, air void content, water binder ratio) lead to the following insights: The used cement type is much more significant for the expansion properties than amount of cement used, air void content and water binder ratio. The alternative testing procedure with a storage solution modelled after natural measured alkali amounts in the road samples showed an over 50% reduced expansion compared to the standard solution at the same testing temperature. An adaption of the standardized testing procedure was advised, distinguishing between upper layer and lower layers of concrete pavements. This would allow a first step for the wider use of aggregates that are considered reactive under current standardized testing but proved sufficient in additional testing procedures and real-life exposure settings.

Occurrence of Delayed Ettringite Formation (DEF) is highly dependent on climatic conditions (e.g. temperature, moisture, rainfall, etc.). Consequently, the induced degradation may develop with various features, depending on the exposure conditions. Moreover, the effect of climate on DEF in concretes using different types of cement still remains unclear.In this context, a joint French-Japanese research program was developed. For three different concrete mixes produced with different cements, material specimens were exposed in the laboratory to different temperatures (from 8 ℃ to 38 ℃): by monitoring expansion in these conditions, the objective was to understand the effect of temperature in simple and controlled conditions. In addition, 30cm-cube specimens were cast and distributed in various field-exposure sites in France and in Japan: this allowed to monitor DEF development in different climatic conditions and thus better understand the influence of complex exposure conditions on the expansion.This paper presents the design of the program (concrete mixes, laboratory and field test setups, exposure site characteristics, etc.). Laboratory test results are presented to illustrate the material characteristics and provide comprehensive details about the effect of temperature on DEF. The DEF potential of each mix has been confirmed. Moreover, for the cements considered in this research, DEF has been influenced in different ways by the temperature.

Considering the importance of the potential effects induced by internal swelling reaction (ISR) on the third barrier of confinement for nuclear power plants and the lack of knowledge on ISR development on massive structure, IRSN launched the ODOBA international project in 2016. Indeed, the knowledge on ISR relies mainly on small-scale and separate effect experiments in laboratories, or medium scale outdoor experiments. Their kinetics and the structure effect of the different parameters involved (temperature, hygrometry, mix, reinforcement…) depend on the studied scale. The ODOBA project is based on experiments on very large concrete blocks widely instrumented, located in Cadarache (France). The concrete mixes are chosen with the objective of developing ISR: either the delayed ettringite formation (DEF), or the alkali-aggregate reaction (AAR), or a possible coupling between AAR and DEF. These mixes have the particularity of being as close as possible to those used for French nuclear reactor containment buildings, but with lower alkali level than former similar experiments. Concerning the 20 tons AAR blocks poured from 2016 to 2018, the residual expansion tests on small samples extracted by coring showed a very weak development of AAR pathology, with a swelling qualified as negligible according to the recommendations in force. An overview of the state of the blocks devoted to AAR is introduced by successively presenting the formulations of the concretes, their characterizations by destructive tests and their follow-up from early age until now without ageing acceleration. The lessons learned give a better assessment of AAR development possibilities for a mix using medium alkali level and classical Potentially Reactive aggregates at very large scale.

The study of structures with alkali-silica reaction problem carried out in CEDEX (Spain) has identified up to seven dams affected by slow expansive processes produced by granitic rocks. Although the reactivity of this aggregates has been demonstrated in real works, the standard tests are not capable of detecting them with the limits proposed in the accelerated mortar bar test (AMBT). To avoid this problem, a new limit is recommended in Spain for the AMBT, when there is a possibility that the aggregate is slow-reactive. This communication presents the study of a dam made with granitic aggregates and unevenly affected by an alkali-silica reaction: no signs of damage to the concrete appear on its right bank versus intense cracking on its left bank. The detailed study of the aggregates used in different parts of the dam (RILEM petrography and AMBT) has made it possible to verify that the damaged areas correspond to the use of slow-reacting aggregates. In contrast, the aggregates are classified as innocuous in both methods where no damage is apparent. Therefore, this study has made possible to verify, within the same structure, the validity of the proposed limit for slow aggregates in the AMBT, and to corroborate how microfractured and deformed quartz produces expansion in the slow-late reaction. Finally, the analysis of the construction process of the dam and the observed distribution of damage has made it possible to demonstrate how important is to evaluate the reactivity of aggregates as quarry faces progress.

Cement is one of the most widely adopted building materials in the world, due to versatility, efficiency, and cost. Cement production, however, is a big contributor to $$CO_{2}$$ C O 2 emissions worldwide.Alternatives are available, based on recycled building materials, industrial by-products, natural minerals, among others, but these are not always as cost-effective and durable as Portland Cement. The processes responsible for the long-term degradation of concrete, made from Portland Cement or otherwise, include corrosion, carbonation, binder-aggregate reactions, sulfate attack among others.This work assesses the long-term durability of alkali-activated alternative binders, namely slag, as compared to regular Portland Cement in concrete under Alkali-silica reaction conditions.Six mix designs were chosen for this study, two using Portland Cement as the binder, and four with slag as the alkali-activated precursor. Out of the four slag mix designs, two used slags from a Canadian source as the primary binders, and two used slag from an European source. Concrete samples were kept at 38 ℃ and 100% RH for 5 years. The performance was investigated by length measurements, microscopic investigations, and chemical analyses using SEM-EDS equipment.It was found that ASR gel chemistry may change over time, both for OPC and Alkali-activated Slag concrete.

The use of supplementary cementitious materials (SCMs), such as silica fume, is an established measure to prevent alkali-silica reaction (ASR). However, the supply of SCMs currently used tends to decrease as a result of sustainable approaches adopted by corresponding producing industries, which motivates the study of alternative SCMs. Various studies have demonstrated that the powder produced by grinding aggregates considered reactive regarding ASR is effective in reducing ASR expansions, improving the durability of concretes produced. Nonetheless, thus far, the mechanisms related to the action of this material have not been elucidated. Therefore, this study aims to provide a theoretical background to contribute to a better understanding of the action of reactive aggregate powder (RAP) in concrete. Based on the literature review focused on studies in which RAP was used to mitigate ASR, we propose an experimental program to fill in the gaps identified in the literature.

Alkali-silica reaction (ASR) is a pathological manifestation that may lead to cracks and further deterioration of the affected structure. As a preventive measure, supplementary cementitious materials (SCMs) are widely used. However, several SCMs used are industrial byproducts whose production tends to decrease as a result of sustainable initiatives adopted by industries in their production process. Thus, several studies have focused on evaluating alternative SCMs. In this regard, studies have indicated that the powder produced by grinding reactive aggregates can reduce ASR expansions. Therefore, this study aimed to evaluate the influence of this reactive aggregate powder (RAP) on ASR expansions in mortars and concretes. Specimens were produced with RAP in the percentages of 10% and 20% replacing cement in mass. The accelerated mortar bar test (AMBT) and miniature concrete prism test (MCPT) were performed. The AMBT results indicated that RAP was effective in reducing the expansions to safe levels. In contrast, from the MCPT results, although reduced, the expansions were above the limit set by the standard. Therefore, the AMBT results were confirmed to be unreliable. Moreover, RAP can be potentially used to reduce ASR expansions. Modifications should be evaluated to reduce expansions to safe levels, such as further grinding of this material.

Alkali-silica reaction (ASR) is a harmful mechanism that can damage concrete infrastructure. Various approaches, including accelerated test procedures, have been developed to assess potential aggregate reactivity in the laboratory. If, on the one hand, these methods are quite established for assessing the reactivity of fine and coarse aggregates, it is still very unclear how to appraise the reactivity and impact of using mineral fillers (MF) in the laboratory. This project aims to understand the effect of MF on ASR-induced expansion and deterioration. Concrete specimens containing reactive and non-reactive coarse and fine aggregates were fabricated with four fillers (derived from ASR-reactive and non-reactive) at a replacement level of 15% using two distinct design approaches (i.e., replacement of PC or fine aggregates). These specimens were stored in conditions enabling ASR-induced development over 360 days, and their expansion over time was monitored throughout. At 360 days of exposure, physical (i.e. porosity), mechanical (stiffness damage test, modulus of elasticity and compressive strength) and microscopic (damage rating index) were conducted. Results indicate that mixtures incorporating MF and replacing PC display changed expansion and damage over time; while granite positively impacted AAR development, the greywacke fillers displayed similar behaviour to control mixtures. On the other hand, limestone and dolomite fillers worsened the expansion and deterioration process.

Currently, the world’s population exceeded 8 billion people on Earth, there will be 9.7 then 10.4 billion people on our planet by 2050 and 2100 respectively. This growth of the world’s population will undoubtedly lead to an increasing demand for concrete infrastructure. However, this material, if the conditions are met, is attacked from interior by the alkali-aggregate reaction AAR. To avoid this mess, the concrete infrastructure can be achieved with the partial substitution of clinker by calcined clays, intended for the formulation of structural concrete. The results of characterization by Inductively Coupled Plasma ICP, differential thermal analysis DTA/TG and x-ray diffraction XRD of Algerian kaolinitic clays highlight the feasibility of partial clinker replacement by certain Algerian kaolin clays, while others are not eligible for partial replacement.

Concrete waste management has become more and more challenging, especially in large cities, encouraging the use of recycled concrete aggregates (RCA). But their mechanical performances are generally lower, limiting their use to non-structural applications. Durability of recycled concrete can also be compromised, specifically if the original concrete is affected by a specific pathology, such as alkali-silica reaction (ASR) which could induce a secondary expansion.In order to prevent water-swelling gel formation, RCA are submitted to carbonation to reduce the quantity of alkali hydroxides and the mobility of the alkali ions in the cement paste. Concrete samples are produced from reactive natural aggregates in the laboratory and crushed at different expansion levels into coarse RCA. At the same time, coarse RCA were reclaimed from distinct members of an ASR affected bridge.Both types of RCA are submitted to accelerated carbonation. Their alkali reactivity is assessed through an autoclave mortar bar test and comparison of expansions with not carbonated RCA and original natural aggregates is performed. Results show that expansions of lab RCA are lower than the ones of original natural reactive aggregates, but higher than the 0.15% limit. In this case, expansions are significantly reduced by carbonation (20 to 50% reduction). On the contrary, expansions of RCA coming from in situ degraded concrete are below the acceptable limit and carbonation doesn't show any effect on the swelling potential.

The decline in fly ash and blast furnace slag production motivated us to look for alternative unconventional aluminosilicate binders such as ground bottom ashes, volcanic ashes, and calcined clays as precursors for producing alkali-activated concrete (AAC). The science of developing mechanical and durability properties of so-called nontraditional precursors-based alkali-activated systems remains less investigated. The study explores the most decisive durability parameters of such systems, alkali-silica resistance (ASR) of different ground bottom ashes (GBA)--based alkali-activated concretes (AAC). Three ground bottom ashes with distinct oxide compositions and amorphous contents are considered. The activator solution used had a silica modulus of 1.25 and a Na2O content of 9.25% by mass of the binder. A solution-to-binder ratio of 0.6 and a binder-to-total aggregate proportion of 35:65 was used. Four different aggregates with varying degrees of reactivity, as established by ASTM C1260, were used. Miniature concrete prism test (MCPT), as specified by AASHTO T 380 for OPC, is used for detecting ASR in the AAC. AAC and OPC prisms are prepared, cured, and exposed to 1N NaOH solution per the code recommendations. The length change of four replicates is monitored for 56 days at designated intervals. All AAC mixtures produced significantly low expansions compared to OPC counterparts, irrespective of GBA compositions or aggregate combinations. We conducted microstructural investigations to validate the expansion results and understand the mechanisms of ASR in GBA-based alkali-activated concrete.

Large scale use of bauxite residue (BR) in cementitious composites has been considered a promising alternative to reduce its landfilling. However, for BR to be considered for commercial use it is imperative to establish that the residue does not compromise the mechanical properties or the service life of structures. The excess alkalis conferred to BR by the Bayer process poses a potential risk to concrete as it could lead to alkali-silica reaction (ASR). To assess the ASR risk, an investigation was conducted in Portland cement (PC)-BR mortar mixtures at three levels of PC replacement (10%, 20%, and 30%). Also, three different Brazilian BRs were tested at a 20% PC replacement level. Results from the accelerated mortar bar test indicate a decreasing ASR expansion rate with increasing BR content, attributed to clinker dilution, despite the high sodium content. The study suggests that mechanisms such as the presence of soluble aluminates and portlandite consumption through pozzolanic reaction play a minor role on ASR expansion. Other possible mechanisms contributing to reduced ASR expansion could be shrinkage and the presence of zeolites in the form of sodalite, a major BR phase. These results contribute towards the safe use of BR as a supplementary cementitious material, potentially adding value to waste as a filler in the construction industry.

The AAR is a detrimental degradation where the natural aggregates play a major role. The increased use of concrete and recycled concrete requires a depth knowledge of the recycled aggregate concrete behaviour and the possible actions to improve the AAR resistance. A block of concrete with strength class C 30/37 was produced. The material was then crushed to obtain 0–32 mm recycled concrete aggregates (RCA). To reduce the porosity of the old cementitious hydrated paste around the aggregates, the RCA were treated with a nanosilica. At the same time, natural siliceous-based aggregates were heat treated up to 650 ℃. Then they were water and air quenched. The AAR reactivity of all aggregates was tested by preparing mortar samples, curing them in water vapour and successively in an autoclave at 150 ℃. The samples were immersed in an alkali-hydroxide solution. The recycled concretes with and without nanosilica and the natural aggregates pre-treated at 650 ℃ and water quenched exhibited a lower AAR susceptibility as compared to the concrete with the same natural aggregates. The heat treatment and quenching at 23 ℃ of the natural aggregates increased the mortar AAR expansion.

The use of recycled concrete aggregates (RCA) has been considered as one of the most promising approaches to reducing concrete’s carbon footprint. Thus, RCA have been increasingly incorporated in concrete in many countries, particularly in Europe and Asia. However, RCA are normally considered as a low-quality material, especially regarding its inner-quality variability along with its potential of being contaminated or exhibiting inherited durability-related issues, for instance if it bears unstable mineral phases, which may react with the cement paste’s alkalis, thus potentially triggering the alkali-silica reaction (ASR). This work aims to appraise ASR-induced product formation and the associated deterioration through advanced imaging techniques, i.e., by coupling scanning electron microscopy (SEM), combined with energy dispersive X-ray spectroscopy (EDS), with X-ray micro-tomography (XMT). Recycled concrete mixtures incorporating a highly reactive coarse aggregate type were cast and stored in conditions enabling ASR development. At 1, 3–4, 11, 16, 20, and 24 weeks, the samples were prepared and investigated with SEM/EDS and XMT. Preliminary evaluations show quite promising results in terms of ASR-secondary product formation and composition along with crack generation and propagation. Further quantitative analysis will help to fully describe ASR-induced deterioration mechanisms triggered by highly reactive coarse RCA.

The concrete industry’s NetZero 2050 roadmaps emphasizes the need of producing eco-efficient concrete where optimization of the concrete’s mix-design and decreasing cement content are among the available options to reduce CO2 emissions by 30%. Previous research has shown suitable performance in the fresh and short-term hardened states of eco-efficient mixtures when mix-designed through particle packing models; however, evaluation of the long-term performance in terms of alkali silica reaction (ASR) remains necessary. This study thus evaluates the expansion and damage due to ASR of two eco-efficient mixtures with two cement contents (325 and 250 kg/m3) in comparison to the standard conventional concrete made with 420 kg/m3 of cement. Overall expansion is governed by the total alkali content, where the eco-efficient mixtures achieved expansion levels of 0.47% and 0.18%, respectively, compared to the control mixture at 0.55%.

The concrete prism test (CPT) is considered the most reliable standardized laboratory test procedure to evaluate alkali-silica reaction (ASR) worldwide; yet to overcome leaching related issues, alkalis are added to the concrete mixture in this procedure. Research on conventional concrete has shown that regardless of the aggregate’s reactivity, the higher the alkali loading, the greater the overall expansion of concrete, indicating that the alkali loading is a key parameter to assess conventional mixtures. However, further research is required to evaluate the effectiveness of applying the CPT to appraise eco-efficient mixtures developed with low cement/alkali content. Hence, this study compares ASR-induced expansion and damage development of two mixtures with distinct cement contents (420 and 250 kg/m3). The mixtures were tested under boosted and non-boosted conditions using the conventional CPT and an adopted encapsulated procedure. The results show that increasing the alkali loading has a greater influence on the overall expansion of mixtures with lower cement content. Moreover, analyzing the damage rating index (DRI) and distress features (without weighting factors) of mixtures with similar expansion, it was concluded that boosted mixtures had more open cracks indicating the impact of accelerating the expansion development caused by the alkali boosting. The results highlight the need for additional research to evaluate and develop ASR-test protocols in order to achieve comparable distress feature data between laboratory and field samples.

Alkali-Silica Reaction (ASR) is a deterioration mechanism in concrete that produces an expansive gel causing expansion and disruption. The conventional approach to mitigate the harmful effects of ASR involves incorporating supplementary cementing materials (SCMs) in the concrete mix. SCMs foster a pozzolanic reaction which reduces the available alkalis in pore solution, one of the ASR reactants. However, the current limited availability of SCMs mandates the identification of alternatives capable of effectively preventing ASR-induced damage.This study explores the use of finely crushed reactive aggregate as pozzolans to reduce or prevent ASR. Three different siliceous aggregates were pulverized to two particle sizes: (i) passing 75 µm, and (ii) passing 45 µm. The pulverized aggregate powder replaced 15% (by mass) of the non-reactive sand in concrete samples. The expansion of these samples was evaluated using the Concrete Prism Test as per CSA A23.2–14. The aggregate powders were used with General Use Cement (GU), General Use Portland Limestone Cement (GUL), and silica fume Portland cement (containing 8% silica fume) to identify the efficacy of the powder with the three types of cement. The preliminary results showed some powder to be more effective than others; however, powder alone was not enough to stop the reaction.

Recycled concrete is an alternative source of aggregates to produce eco-friendly concrete. However, some recycled concrete aggregate (RCA) sources may have been contaminated by previous deterioration mechanisms, such as alkali-silica reaction (ASR). Although it has been demonstrated that ASR-affected RCA continues to progress through secondary expansion in new concrete, the prevention approaches for ASR-affected conventional concrete may not be efficient for RCA-concrete. A Scoping Literature Review was conducted to assess the state-of-the-art of ASR prevention in RCA-concrete. Five supplementary cementitious materials (SCMs) and lithium nitrate were the most common materials used to prevent ASR in RCA-concrete, tested using five different methodologies. Since ASR-affected RCA concrete is prone to secondary induced expansion, depicting a need to characterize RCA material regarding deterioration source (i.e., reactive coarse and fine aggregate) and previous level of damage, enabling adjustment of the prevention specifications accordingly.

The main source of crushed stone for concrete in Montevideo, Uruguay, is the granodiorite quarry. The aim was to evaluate the potential reactivity of this crushed stone and determine the expansion of concrete produced with recycled concrete aggregate (RCA), including the granodiorite. The concrete prisms from the accelerated expansion test were crushed once the evaluation in granodiorite was completed. Then the crushed concrete was used as coarse aggregate (at 25% and 75% replacement of non-reactive coarse aggregate) to evaluate the expansion in prisms kept at 60 ℃ and 95% RH for 13 weeks (accelerated methodology) and in prisms kept at 38 ℃ and 95% RH for 40 weeks (traditional methodology). Petrographic analysis of the granodiorite rock showed the presence of microcrystalline quartz as a reactive constituent. In accordance with the expansion in the concrete prism test using the traditional methodology, four samples exhibited reactivity while one did not. However, according to the accelerated methodology with an expansion limit of 0.08%, only two samples displayed reactivity. The concrete containing RCA exhibited greater expansion compared to the reference concrete (which employed non-reactive aggregate) but remained within acceptable limits. The results indicate that the use of RCA derived from concrete containing the studied granodiorite crushed stone resulted in a similar expansion compared to the original concrete. This suggests that the potential reactivity of the granodiorite coarse aggregate persists, even after it has previously undergone a reactive process within concrete.

In the current need to offset greenhouse gas emissions, interground Portland Limestone Cement (PLC) emerges as a viable sustainable alternative, offering the potential to reduce clinker content. However, the durability of employed PLC, especially with high limestone fillers (LFs) replacement ratios exceeding 15%, requires detailed investigation. Durability concerns, notably in relation to sulphate attack and steel corrosion, remain unresolved, though the reduced pH due to LFs addition in PLC could help mitigating alkali-silica reaction (ASR). In this context, this work evaluates ASR development in concrete mixtures incorporating PLC with interground LFs ratios of 15%, 20%, and 25%. Analysis of expansion over from accelerated mortar bar (AMBT) and concrete prism tests (CPT) reveal that a replacement ratio of up to 25% does not significantly impact ASR-induced expansion. This finding highlights the potential of PLC for sustainable construction without compromising durability regarding ASR.

Recycling construction and demolished waste is an effective way to reduce concrete production's environmental impact. However, the presence of past deterioration is always a concern when using recycled concrete aggregate (RCA). To understand the effect of pre-existing damage in each component (original aggregate vs residual mortar) and secondary ASR-induced damage, recycled concrete specimens are manufactured in the laboratory incorporating RCA displaying distinct ASR past deteriorations using two types of reactive aggregates (i.e., reactive coarse and reactive sand). Two levels of secondary expansion were selected for analysis (0.05% and 0.30%). Later the specimens were mechanically tested for compressive strength, direct shear strength and stiffness damage test (SDT). The results showed that the source and extent of initial damage impact the mechanical properties loss of recycled concrete. Additionally, the results were combined with the microscopic assessment, the damage rating index (DRI), of the specimens for each secondary expansion level. The results indicate that crack propagation due to ASR origin influences the mechanical responses.