THEDESCO

Understanding the thermal deformations of cement-based materials is crucial to ensure the performance of building envelopes and infrastructures subjected to thermal loads. Thermal deformations are recognized as one of the major causes of cracking of cement-based materials. The prediction of thermal deformations relies on an accurate description of the thermal properties, namely the coefficient of thermal expansion (CTE), the heat capacity (a property related to the increase of temperature of a material upon heating) and the thermal conductivity. Sensitivity analysis shows that relatively small variations in the heat capacity and in CTE may significantly affect the thermal response of concrete structures. For cement-based materials, these properties are reported to be composition, time, temperature and relative humidity (RH) dependent. The goal of this project is to provide a model of the thermal properties of cement-based materials that are informed by the relevant physical phenomena in a multiscale framework and that can be used in the engineering practice. The target applications are concrete infrastructures and building envelopes made of cement-based materials that are subjected to thermal loads in an environment with a given RH. We will focus on the elucidation of the physical origins as well as the temperature and RH-dependency of the CTE and the heat capacity. We assume that accounting for the multiscale nature of cement-based materials is crucial to understand thermal deformations since key aspects of the thermo-mechanical behavior of cement-based materials are related to nanoscale processes. To tackle this problem, we propose a strategy combining molecular simulations, micromechanics and finite element analysis. Additionally, a major part of the project will be devoted to gathering data to create a database on the thermal properties of cement-based materials that will be used for validation of the model according to various environmental conditions and compositions of the materials. Molecular simulations are adapted to assess the behavior of water confined at nanopores because they allow quantifying the intermolecular forces associated with adsorption phenomena and confinement. Micromechanics will be used to bridge the scales from the molecular scale up to the scale of industrial application of cement-based materials. Finite elements simulations will be used to study the thermal deformation and cracking at the macroscopic scale. The expected outcomes of this project will contribute to reduce the empirism in thermo-hydro-mechanical modelling of concrete that can leads to the design more durable and resilient structures tailored to performance specifications, the extension of the service lives existing ageing infrastructures, and the reduction of the impact of using concrete.