Direct tensile failures of concrete with various moisture contents and sizes at low temperatures via mesoscale simulations with ice explicit modelling

The enhancement of mechanical properties of concrete meso-components and the interaction caused by non-uniform deformation as well as phase change can cause significant changes in the macro-mechanical performances of concrete at low temperatures. Based on the action mechanism of the above low-temperature effect, this paper established a thermal-mechanical sequential coupled simulation method with explicit modelling of pore ice at the mesoscale level to quantitatively investigate the direct tensile failures and the corresponding size effect of concrete with four structural sizes (D75, D150, D225 and D300) and three moisture contents (2.0 %, 4.0 % and 6.0 %) at different temperatures (20, -30, -60 and -90 degrees C), in term of failure mode, deformation curve, peak strength and residual strength. The numerical results show that the direct tensile peak strength performs an obvious low-temperature enhancement effect due to the more damaged aggregates and more areas being in a state of multi-axial stress caused by low-temperature non-uniform stress field. However, with the decreasing temperature, the residual strength shows a decrease trend and the trend slows down with the increasing moisture content. Besides, as the temperature drops from 20 degrees C to -90 degrees C, both the size effects on direct tensile peak strength and residual strength are strengthened (with the increase approaches nearly 200 % for peak strength while 33 % for residual strength). Finally, a modified size effect theoretical model was developed considering the quantitative coupling effects of low temperature and moisture content. The present research results can provide a reference for the performance evaluation and safe design of large-sized concrete exposed to low-temperature environments.