Molecular modeling of the thermo-hygro-mechanical response of C-S-H

The comprehension of the thermo-hygro-mechanical response of cement-based materials (CBM) is key for ensuring the durability and long-term performance of CBM structures such as concrete (infra-)structures and building envelopes. Assessing the thermal response of CBM requires a precise determination of three main properties : heat capacity, thermal expansion, and thermal conductivity. The threethermal properties are known to be dependent upon the relative humidity and the temperature. As the main phase produced during cement hydration, C-S-H accounts for the majority of porosity in cement-based materials, featuring both gel (with diameters between 2-50 nm) and interlayer (with thickness< 2 nm) porosity. Water confined in C-S-H is known to behave differently from water in capillary porosity. Quantifying the effects of confinement in fluids represents a significant challenge considering the length and time scales that are needed to be probed. Molecular simulations are particularly well suited to assess the behavior of confined fluids since they enable the quantification of inter-atomic forces, structural changes, and other nanoscale processes responsible for the anomalous behavior of confined fluids. In this context, the principal goal of this thesis is to study with molecular simulations the thermo-hygro-mechanical response of C-S-H under temperature and relative humidity variation. Our focus will be on elucidating the physical phenomena at the origin of the material's hygrothermal behavior, including sorption and thermal pressurization. The specific objectives include : (i) Modeling the atomic structure of C-S-H and understanding the role of the disjoining pressure on sorption-induced deformations of cement-based materials ; (ii) Investigating sorption in C-S-H and how the temperature, relative humidity, and confinement affect it ; (iii) Studying the heat capacity and thermal expansion of C-S-H under temperature and relative humidity variation ; and (iv) Studying thermal pressurization in C-S-H under different poromechanical conditions. The results presented in this thesis represent an important contribution to multiscale modeling and could offer new insights into the physical mechanisms behind the thermomechanical behavior of cement-based materials.