Thermo-mechanically-induced thermal conductivity change and its effect on the behaviour of concrete

Abstract Concrete structure can be damaged when subjected to high temperatures due to the mismatch of thermal expansions between the material constituents. The damage results in the initiation and growth of cracks, particularly on the interface between constituents, which decreases the effective thermal conductivity. This phenomenon is usually modelled by a mesoscale approach, where concrete constitutes three phases: aggregates, cement matrix and interfacial transition zones (ITZ). This paper aims at studying the thermo-mechanically-induced thermal conductivity change and its effect on the behaviour of concrete when exposed to both mechanical and thermal loads. It consists in a mesoscale modelling using lattice discretisation in which the aggregate is elastic, while the cement matrix and the ITZ are described by an elastic-damage model. Thermal conductivity of a cracked element is related to damage variable via crack opening. The model was validated against experimental data for a sample subjected to different temperatures. The thermal conductivity decrease versus temperature was also quantified during uniaxial compression tests for a large range of temperatures to highlight the effect of temperature and of temperature gradient. Comparisons with experimental and numerical studies show the need of taking into account the thermal conductivity variation when modelling concrete structure under thermo-mechanical loads.