Multi-scale and multi-physics processes make understanding the mechanical impact of alkali-silica reaction (ASR) on structure challenging. This study investigates ASR's impact on a small-scale mortar foundation subjected to reinforcement pull-out. A 1/50 scale electrical pylon foundation is tested in an X-ray tomograph at different ASR swelling stages. Finite-element-based digital volume correlation is used to analyze the structure's behavior during loading. Results show that the pull-out resistance of small-scale foundations increases with ASR and the failure patterns change. Through measurements of displacements within the mortar, interfacial debonding, and multidirectional swelling, this increase is attributed to reinforcement prestressing caused by ASR swelling. In-situ tests combined with Digital Volume Correlation allow for precise quantification of threedimensional displacement fields in the specimen. Such a method highlights the effects of alkali-silica reaction, enabling a quantified understanding of the relationship between structural response and pathology progression.

This study aims to provide insights into the location of expansion due to alkali–silica reaction (ASR) by quantifying deformations during the early stage of expansion of a single reactive andesite aggregate embedded within cement paste. One-month time-lapse microstructural information was obtained by performing global (low-resolution) and local (high-resolution) X-ray computed tomography (CT) on the specimens. High-resolution scans were used to measure displacement fields using mechanics-informed digital volume correlation (DVC). The CT images revealed the formation of cracks inside the aggregate along its surface after 14 days, followed by crack opening and propagation. The DVC results showed outward-directed displacements from the inner surface of the aggregate, indicating the presence of expansive sites on the surface, even when no crack was observed in the CT images. After cracking, large displacements developed in the direction perpendicular to the cracks. The mechanisms of ASR expansion pressure generation, which explain the observed deformation and crack changes, are discussed in relation to previous propositions.

A comprehensive thermodynamic database for Na/K-ASR products in the CaO-SiO2-Na2O-K2O system is developed by integrating experimental solubility data and data from molecular simulations, enabling the determination of standard thermodynamic properties. Equilibrium thermodynamic calculations are then used to construct binary and pseudo-ternary phase diagrams and to analyze the effects of temperature, calcium content, and alkali composition in ASR. The thermodynamic competition between ASR products and alkali-bearing C-S-H is quantified, providing insight into alkali uptake mechanisms and phase coexistence. We predict the formation of Na-shlykovite and Na-magadiite (or alternatively Na-kanemite at temperatures below 25 degrees C) in CaO-SiO2-Na2O systems, and of K-shlykovite together with ASR-P1 in CaO-SiO2-K2O systems. The formation of these ASR products is intimately linked to the formation of alkali-bearing C-S-H. The phase diagrams corroborate the thermodynamic incompatibility of portlandite with ASR products. The diagram built for various temperatures provides a way of evaluating the representativeness of accelerated ASR testing under increased temperature conditions. Finally, the propensity to generate a crystallization pressure is evaluated according to the phase diagrams.

Several mineral analogues were proposed for ASR products, but no consensus exists on which ones best represent crystalline phases or could serve as templates for nanocrystalline or defective forms. This study reviews all structures reported in the literature for crystalline ASR products within the SiO2–CaO–Na2O–K2O–H2O system. The research develops the first atomic model database that includes both Na- and K-based ASR phases. These structures are simulated using Density Functional Theory (DFT) and classical Molecular Dynamics (MD). The work calculates and reports crucial data, including thermodynamic properties (heat capacity, entropy, and enthalpy of formation), self-diffusion coefficients of water and alkalis, elastic and thermoelastic properties. Furthermore, it quantifies the potential for generating crystallization pressure of each mineral analogue, which is key to ASR-induced expansion. Ultimately, the study discusses the structural and thermodynamic relevance of the investigated phases to determine their suitability as crystalline analogues for ASR reaction products.

Interlayer species play a critical role in the thermo-hydro-mechanical properties of C-S-H at the molecular scale. We investigate how different choices in molecular modeling of C-S-H impact the behavior of interlayer species and subsequently affect the thermal, mechanical, and transport properties. By comparing various force fields, we identify the most effective approach per property. The choice of water force field has minimal influence on properties. As for heat capacity, we show that accounting for quantum corrections is important in calculating the thermal conductivity of C-S-H. Different choices of force fields lead to better agreement of estimates of the heat capacity, thermal conductivity, and thermal expansion of C-S-H with available experimental data. Non-reactive and reactive force fields exhibit similar behavior in tensile and shear tests. ClayFF Ca(aq) leads to a reduced interlayer diffusion coefficient. This research underscores the imperative role of accurately characterizing interlayer species in understanding C-S-H behavior.

Concrete spalling is a thermo-mechanical instability induced by fire exposure that needs to be investigated when the fire behavior of specific structures is to be assessed. In Europe, experimental fire behavior is commonly assessed by reference to EN 1363-1 “Fire resistance tests – Part 1: General requirements.” According to this standard, conditioning at 23°C, 50% RH for at least 3 months should be applied for concrete elements but it is also specified that at the time of the test the strength and the moisture content of the test specimen shall approximate to those expected in normal service and the test specimen shall preferably not be tested until it has reached an equilibrium moisture content resulting from storage in an ambient atmosphere of 50% relative humidity at 23°C. In this context, the main objective of this work is to study the impact of drying duration and conditions on (i) the spalling profiles of different concrete and (ii) the associated moisture profiles. An accelerated drying protocol is proposed based on an extensive experimental campaign and a numerical drying kinetics study on two high-performance concretes, and two ordinary concretes. The accelerated drying protocol aims (i) to propose a protocol allowing to reproduce of the hydric state of concrete structures in service condition (2 years) while ensuring the reproducibility of the spalling facies and secondarily (ii) to explore the possibility to reduce the conditioning time usually used in standard conditions (3 months) while maintaining acceptable representativity. The fire behavior of mechanically loaded and non-loaded slabs was evaluated at various times and conditioning modes. The important influence of the moisture gradient and the moisture content on spalling are highlighted. A good representativity of the proposed accelerated drying protocol is also observed.

Establishing direct relations between alkali-silica reaction (ASR) expansion, crystallization pressure build-up, and phase assemblage changes is a critical step towards predictive modeling of ASR damage. To address this, we propose a strategy that combines thermodynamic modeling with micromechanics. First, we complete the thermodynamic database for ASR products, including nanocrystalline ASR-P1 data and improving the previous data for crystalline products. Phase assemblage is determined by accounting for cement hydration and amorphous silica dissolution kinetics. Crystallization pressure estimates are provided based on pore solution supersaturation with respect to ASR products. These phase assemblage and crystallization pressure estimates are then used as input for analytical micromechanical estimates of elastic properties degradation and macroscopic expansion. The model strategy that integrates damage considerations and the gel-like nature of ASR-P1 provides a better comparison with experimental results.

Biobased concretes, such as flax or wood concretes, are ecofriendly materials that benefit excellent hygrothermic and acoustic properties. They are usually combined with a loadbearing wooden structure, but recent studies show that those concretes can reach masonry-like compressive strengths, which suggests their potential use for structural elements. However, the lack of data on its delayed mechanical behavior is an issue to their development. This article describes the study of the drying and shrinkage, in controlled environments (22 ℃, 50

Sorption processes are critical for the drying and durability of cement-based materials, directly affecting their thermal properties. Temperature can substantially influence these processes. This work uses molecular simulations to study sorption in C-S-H pores under varying temperatures and relative humidity, considering pore sizes from the gel to the interlayer scale (between 11.6 and 106 Å). We quantify the temperature and pore-size dependence of water cavitation and sorption hysteresis in the C-S-H pores. The critical pore sizes for the disappearance of hysteresis and the reversibility of capillary condensation are identified, with the former being directly associated with cavitation. We show that cavitation occurs only in gel (meso)pores when they are above the critical pore size and below the critical temperature for cavitation. Interlayer pores, a major class of micropores in C-S-H, are not subjected to cavitation. Cavitation in C-S-H pores is homogeneous, occurring in the bulk-like zone of mesopores. The hydrophilicity of the C-S-H surface increases with the temperature, making heterogeneous cavitation less likely to occur. The results above were obtained consistently with three different force field parametrizations, building confidence in their relevance to describe C-S-H interfacial behavior. Finally, we demonstrate that macroscopic considerations for pore emptying and filling, such as the Kelvin-Cohan and equilibrium Derjaguin-Broekhoff-de Boer equations, are not valid or inaccurate when desorption occurs through cavitation in C-S-H. These results are relevant to understanding the sorption processes in other nanolayered adsorbing materials.

Thermal and themo-mechanical properties of alkali-silica reaction (ASR) products are poorly studied. The existent property data refers to theoretical considerations and do not account for the fact that ASR products can be crystalline, nanocrystalline and potentially amorphous. Here, the thermal conductivity, heat capacity, and coefficient of thermal expansion of crystalline structures (based on Na- and K-shlykovite), nanocrystalline structure (based on defective K-shlykovite structures), and amorphous ASR product are calculated using molecular simulations. Semi-classical estimates of the thermal conductivity, heat capacity, and standard molar entropy are provided. The anisotropy of thermal conductivity and thermal expansion is quantified. Nanoacoustics parameters (sound velocities, phonon free path and relaxation time) are calculated. These results contribute to completing property data for ASR products.

Molecular simulations are performed to decipher the nanoscale processes associated with water sorption in tobermorite, a microporous phase that functions as the binder in autoclaved aerated cement composites. Merlino's cross -linked tobermorite 11 & Aring; is studied. We show that there is no hysteresis in bulk tobermorite at the molecular scale because the zeolitic cavities occupied by water are smaller than the critical pore size for hysteresis disappearance, and upon sorption, tobermorite 11 & Aring; shows virtually no volume change. These effects combined explain why hysteresis under sorption in tobermorite is limited. Similar explanation could also explain absence of significant hysteresis in some layered double hydroxides present in cement systems.

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.

Moisture transfer is a very common phenomenon in a wide range of engineering fields, such as civil engineering (cement-based constructions), food processing, mining and soil penetration, drying and imbibition of porous media (including phase change materials), etc. Based on the diffusion assumptions, the classical adopted model (especially for drying) is completed by the liquid permeation. However, it is still inadequate to compromise the complexity of the porous structures. In this work, a “parallel-series” assumption of moisture transferring pattern is proposed, comprising different forms of moisture presence and the coupling styles, achieved by an interpolation factor to cover all the possible contribution ratios of the two patterns. The drying of porous material is performed under two ambient conditions over 160 days on both local and global parameters, i.e., relative humidity (RH) and mass loss (ML). In the simulation part, a nonlinear diffusion-drying model containing liquid permeation and vapor diffusion in the transfer mechanism is applied to estimate the drying process, and compared with the experiment data. Results show different tendency for the two cases of either the permeation dominating case or the no-dominating case. This approach also clarifies the transition from evaporation of weak permeability for vapor diffusivity (square root behavior) towards the linear and faster behavior, which is observed in more porous and permeable materials for the vapor diffusion.

In service conditions, reinforced concrete structures are multi-cracked due to the loads they are submitted to.It enables aggressive agents, such as chlorides, to penetrate the concrete cover and could initiate steel rebar corrosion leading to more structural damage.Some experimental programs focusing on chloride penetration were conducted on plain or cracked concrete, but mainly unloaded and unreinforced concrete specimens were used for the measurement.These tests highlight the linear dependence of chloride diffusivity to crack opening.However, they do not take into account the presence of rebar, and cracks are partially or totally closed up during the test, which is different from service conditions.This research project aims to understand the influence of micro-and macro-cracks on chloride diffusivity in conditions close to the service ones.To achieve this objective, three steady-state accelerated migration tests under electrical field are to be carried out on a same reinforced concrete specimen kept under a tensile load representative of a structural one.This non-standard chloride penetration test requires the adaptation of the experimental protocol.This paper presents preliminary adaptation work using numerical simulations developed with Comsol Multiphysics®.The impact of testing configuration and parameters, as well as cracking was investigated.Comparison of simulations and preliminary experimental results are also given.

New in-situ microscopic mechanical tests in Environmental SEM (ESEM) and climatic chamber (CC), assisted by Digital Image Correlation (DIC) technique, have been developed. The developed testing frameworks speed up the drying duration at least 200 times compared to classical test methods. We mitigate the risk of cracking to focus on the intrinsic drying creep and shrinkage. Free drying shrinkage is assessed at a micro-scale and exhibits a high correlation with the mass loss for relative humidity above 60% relative humidity (RH). We observe a water cavitation effect between 50–60% (RH). Although the drying conditions in ESEM occur at low pressure compared to ambient air-drying conditions in a climatic chamber, the shrinkage deformations at equilibrium at 20% RH are quite the same. The evolution of desiccation creep with drying shrinkage is bilinear in uniaxial and linear under biaxial compression. The drying creep Poisson's ratio is negative, between −0.1 and 0.

Thermal desorption is a critical process in cement-based materials subjected to temperature increase. C-S-H surface is the most likely surface available for thermal desorption in these materials. Here, we investigate surface thermal desorption in C-S-H. Molecular simulations are used to get systems equilibrated under two drained poromechanical conditions: liquid water-saturated and constant partial fluid pressure conditions. Suited fluctuation formulas are deployed to acquire properties at the adsorbed layer level. We show that thermal desorption is driven by thermal expansion of water and liquid-to-vapor phase transition (leading to cavitation). The potential energy, isochoric specific heat capacity, molar incremental enthalpy, bulk modulus, coefficient of thermal expansion, surface tension, and pressure tensor components exhibit a marked dependence on the distance from the C-S-H adsorbing surface. Parameters usually adopted in sorption models (e.g., BET family) such as monolayer thickness and adsorption energy need to be revisited using molecular scale evidence.

Calorimetry is the standard measurement method for monitoring the hydration of cementitious materials and retrieving their hydration degree. However, it is destructive and impractical for in situ measurements. Electromagnetic measurements are sensitive to the changes in the porosity and water content of materials, making dielectric techniques good candidates for characterizing the hydration of cementitious materials. Besides, they can be implemented in a noninvasive way by means of microwave reflectometry sensors. In this article, the hydration of a cement mortar is monitored using both calorimetry and microwave reflectometry at 800 MHz, over a 140 h period covering its hydration process. The measured calorimetry and dielectric data prove to be consistent with each other as well as with the phenomena at stake along hydration. Besides, the combination of this data is carried out to obtain the variations of the mortar dielectric permittivity as a function of the hydration degree. On the other hand, we develop a dielectric model for monitoring the mortar hydration degree. The latter, which is based on mixing equations, accounts for the age-dependent mortar dielectric properties due to the hydration process and porosity decrease experienced by cementitious materials, especially at an early age. This model is the first mechanistic approach to describe the dielectric properties of mortar during hydration. Thus, in order to retrieve the hydration degree, the used model implements mean-field homogenization based on the dielectric features of the mortar constituents. The combination of calorimetry and dielectric experimental data is compared to the dielectric model of hydration, showing good agreement.

In France, buildings’ heating systems represent 45