This study aimed to investigate whether the expansion due to delayed ettringite formation (DEF) results in anisotropic mechanical properties similar to those alkali-silica reaction (ASR) expansion. To this end, DEF expansion tests were performed under biaxial restraint, and compression tests were conducted with loading directions perpendicular or parallel to the crack orientation. The experimental results showed that cracks oriented perpendicular to the loading direction caused a greater reduction in the mechanical properties than those aligned parallel, indicating anisotropic behavior similar to that observed in ASR. Additionally, an index based on crack characteristics (length and angle) was developed to quantify the anisotropy induced by DEF in the mechanical properties, and its applicability was confirmed.

Many concrete structures worldwide suffer from internal swelling reactions, mainly Alkali-Aggregate Reaction (AAR) and Delayed Ettringite Formation (DEF). AAR is caused by reactive silica in aggregates reacting with alkalis in cement, while DEF results from high early-age temperatures and specific cement compositions. Despite different origins, both lead to similar damage: cracks, deformation, internal stress, and reduced durability. Diagnosis starts with microscopic and chemical analysis of core samples. Both require data on cement composition, structure, and environmental conditions. Water greatly influences swelling but is difficult to measure in situ. DEF also needs early-age temperature and heat of hydration details. Additional lab or on-site tests may support diagnosis. This methodology compares AAR and DEF affected structures assessment including the use of a 3D numerical model to simulate, validate and predict their structural behaviour.

Transport and dissolution mechanisms govern the Alkali-Silica Reaction (ASR) sequences. Ion diffusion by concentration gradient triggers dissolution, which leads to the precipitation of new phases, initiating pressures that cause the aggregate cracking. Quantifying these transport and kinetic properties is therefore essential to assess aggregate reactivity and to support predictive modelling. An experimental campaign for the characterization of diffusion coefficients and dissolution rates has been conducted. Four aggregates, representative of various kinetics and level of expansion in similar concrete conditions, were selected: greywacke, limestone, quartzitic sandstone and a non-reactive quartzite. Diffusion coefficients were measured using X-ray spectroscopy. Iodide ions (1M I-) were used as a conservative tracer. Both parallel- and perpendicular-to bedding diffusion coefficients were measured. For dissolution properties assessment, aggregates were immersed in a basic solution to promote the degradation of the silica reactive microstructure. Two particle size fractions for each aggregate (0.5-1 mm and 1-2 mm) and three temperatures (25, 40 and 60°C) were considered. The study displays the diffusion parameters and dissolution rate coefficients for the four aggregates. The values of effective diffusion coefficient determined lie within a wide range, from 10-11 to 10-15 m²/s, which strongly influence the reaction sequence according to aggregate nature. The dissolution rate values are in the range from 10-11 to 10-13 mol/(m².s). The combined analysis demonstrates that diffusion and dissolution processes control ASR advancement by governing the characteristic time of aggregate degradation. The data provided constitute valuable input for improving the evaluation of ASR kinetics through predictive modelling.

Non-destructive testing (NDT) methods are key tools for monitoring concrete structures, as they offer the advantage of detecting structural defects over time without causing additional damage. Additionally, internal swelling reactions have been identified as pathologies responsible for structural defects in many structures worldwide, often leading to demolition and expensive repairs. It is therefore particularly important to develop the application of NDT methods for monitoring damage in the affected structures. Based on this context, this research aims to study the application of NDT methods in monitoring damage caused by internal swelling reactions including alkali-silica reaction (ASR) and delayed ettringite formation (DEF). To this end, control and damage-induced specimens were cast and stored fully immersed in water at 380C for monitoring. The monitoring was carried out using NDT methods including resistivity, linear vibration and ultrasonic pulse velocity (UPV). The results showed that resistivity can effectively monitor alkali leaching in concrete affected by ASR and DEF. Linear vibration was capable of monitoring all stages of ASR and DEF, including damage acceleration, stabilization, and recovery. UPV, however, showed lower sensitivity to damage caused by ASR only. The findings related to resistivity and linear vibration can be used to develop predictive relationships and enhanced monitoring strategies for structures affected by ASR or DEF.

Delayed ettringite formation (DEF) is an origin of concrete degradation and can cause serious damage to major engineering structures. A methodology for carrying out a numerical analysis of DEF-affected structures is proposed in order to offer diagnosis and prognosis and thus optimise their maintenance. A methodology in two phases, calibration and validation, was developed and applied to laboratory beams presented in the literature, with different reinforcement ratios, uniformly heated at young age and subjected to water gradients. At present, few numerical models are capable of faithfully reproducing the behaviour of structures damaged by DEF at this scale because of the diversity of phenomena to be considered (shrinkage, creep, temperature, alkali leaching, pressure generated by the DEF, anisotropic cracking). A thermo-hydro-chemo-mechanical model was applied. The modelling results showed good accordance with observations. However, multiphysics parametric analyses are necessary to obtain relevant calibration owing to the high non-linearity of the phenomena. A methodology applicable to field work was also developed, taking into account the heterogeneity in the temperature reached at young age and the probable lack of calibration data.

The permeability of concrete is a key parameter to evaluate the durability of reinforced concrete structures. In the nuclear field, the tightness of containment buildings largely depends on the low permeability of prestressed concrete. These structures are heavily reinforced raising the question of how reinforcement bars and prestressing cables affect the apparent permeability compared to plain concrete. Usual standardized permeability tests have limitations. The small sample size makes it challenging to study the effects of reinforcement. Additionally, confinement within test cells can alter interface quality, potentially closing cracks in damaged concrete. This can modify the flow characteristics and impact the representativeness of the measured permeability. To address these issues, a new apparatus has been developed to measure permeability under vacuum for reinforced concrete elements. The measurement is performed on prismatic specimens in two directions. This paper presents the system and its validation on plain concrete, as a preliminary step before applications on reinforced concrete. The results indicate a significant anisotropy in permeability depending on the orientation of reinforcement bars. The experiments reveal the minimal resistance of steel-concrete interfaces to pressure gradients, irrespective of the saturation degree.

Managing the effects of Internal Swelling Reactions (ISR), Delayed Ettringite Formation (DEF), and Alkali-Silica Reaction (ASR) on the integrity of concrete structures with containment functions, such as nuclear facilities and dams, remains a major challenge for both long-term operation and maintenance. However, the effect of cracking caused by ISR on the mass transport properties of concrete has not been extensively investigated. To date, there is limited characterization of water diffusive phenomena and permeability in concretes affected by ISR. To address these gaps, a comprehensive and complete characterization of mass transport properties evaluating water porosity, pore distribution, diffusivity, and apparent air permeability in concrete affected by ASR and DEF is conducted hereafter. This experimental work points out the impact of cracking induced by expansion on these parameters. Water diffusivity is multiplied by a maximum of 2.8 for 0.22% expansion in DEF, while permeability can be multiplied by 44 for ASR concrete after expansion to 0.22%. The cracking patterns induced by ASR and DEF are different, leading to differences in the evolution of transport properties. Overall, crucial experimental insights to enhance existing models are thus highlighted, particularly concerning the intricate relationship between expansion advancement, cracking, and mass transport properties in concrete.

Alkali-Silica Reaction (ASR) is a long-term chemical degradation induced in concrete by the difference in pH between the aggregate and the cement paste. ASR advancement is thus driven by the combination of the ionic species diffusion and the dissolution of reactive silica. In this paper, the reactive transport model is based on the principal sequence of the ASR-mechanisms: hydroxide, alkali and calcium diffusion, silica dissolution and reaction products precipitation. First, the proposed model highlights the impact of the competition between diffusion and dissolution kinetic on the formation of products in the depth of the aggregate particles according to the calcium concentration. Secondly, the numerical study on the size effect of the aggregate particles highlights the efficacy of this approach to reproduce the dependence of the products type formed during precipitation, allowing for the competition between ASR and pozzolanic effect to be reproduced.

Alkali silica reaction (ASR) is a harmful swelling pathology in concrete influenced by various factors such as moisture levels and stress conditions. In order to evaluate ASR-damaged structures, it is essential to characterize in situ water saturation gradients and to quantify the influence of reinforcement on ASR-induced damage. This research aims to assess the capability of different non-destructive testing (NDT) methods to evaluate moisture gradients in the context of ASR as well as the damage arising from expansion gradients in presence of reinforcement. Plain and reinforced concrete specimens were cast using both reactive and control composition. After curing, the specimens were fully, half-immersed and quarter-immersed in water at 38 degrees C to monitor the effects of ASR under varying water saturation conditions. The physicochemical conditions were characterized using permittivity tests. Expansion and damage were monitored through two-dimensional length change measurements, linear vibration analysis, acoustic emission (AE) and crack observations. This paper proposes an original method involving AE monitoring during mechanical loading following expansion. The linear vibration method was found to correlate the extent of damage with average expansion, regardless of the moisture gradient or presence of reinforcement. The acoustic emission during mechanical loading, along with crack observation techniques, effectively localized damage resulting from moisture gradients and reinforcement effects. The discussion highlights the complementary nature of these two techniques for monitoring the damage in both plain and reinforced concrete subjected to ASR.

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

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.

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.

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 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.

Air permeability measurement is critical for assessing the integrity of nuclear containment structures, especially in safety-critical environments such as nuclear power plants. This method provides a rapid assessment of leak rates and has the advantage of being non-destructive for field applications. However, existing tools, such as the Cembureau permeameter, are limited to laboratory environments and require specific conditions that are not suitable for real structures. This limitation underscores the need for novel, non-destructive, in-situ measurement techniques, as core sampling structures for analysis are not always feasible. The results presented here concern three different concretes whose permeabilities were measured using the Cembureau under pressure and in vacuum, a unique vacuum measuring cell, and the Torrent Permeameter Tester, also used in vacuum. All these tests differ either in the type of regime, the duration of the test or the pressure. However, we are now able to obtain similar permeability results regardless of the technique used.

In the context of concrete structures ageing, the study of cementitious material durability is of critical importance, particularly the degradations caused by the Alkali-Silica Reaction (ASR). This reaction is driven by the reactive silica dissolution of the concrete aggregate and can unfold in different manner according to the aggregate. The goal of the study is to improve the evaluation of the aggregate reactivity, in terms of quantity of reactive silica and dissolution rate, linked to the form and state (crystalline, amorphous, micro-crystalline) of the aggregate structure. Four aggregates were selected for this study: Potsdam sandstone, Springhill greywacke, Spratt limestone, and a non-reactive Quartzite (used as a reference). For dissolution properties assessment, the aggregates were immersed in a basic solution to promote the degradation of their reactive structure. To reproduce an idealized highly alkaline solution close to a concrete pore solution, dissolution tests were performed on a 1M NaOH solution. Two particle size fractions for each aggregate: 0.5 mm–1 mm and 1–2 mm (with a solid to solution mass ratio of 1:4) and three temperatures: 25, 38, and 60 ℃ were considered. Silica concentration in the solution was measured by complexometric titration. The study displays the dissolution rate constants and analyses the cause of the differences in dissolution.

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.

This paper addresses the challenge of evaluating the air permeability of structural concrete in situ, using non-destructive techniques. Specifically, it aims to reconcile air permeability measurements made in the field with those made in the laboratory. Permeability measurements in the laboratory and in the field use both under pressure and in vacuum techniques in steady or unsteady states. Differences between the methods may arise from pressure or flow regime variations, or flow direction control. The study proposes a methodology for evaluating air permeability in the field using an existing vacuum technique and an original numerical inverse analysis. An experimental programme using different protocols of permeability measurement with vacuum techniques analysed by numerical modelling is used to understand the differences observed experimentally.

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.