Influence of Sand Particle Size Distribution on the Properties of Mortars Subjected to Various Temperatures

The durability of concrete and mortar structures against extreme thermal stress is a major concern in Civil Engineering. This present experimental study aims to critically assess the influence of sand particle size distribution on the physico-mechanical and hydric characteristics of mortars after exposure to different temperatures. Cubic mortar specimens measuring 70 x 70 x 70 mm were manufactured using two types of sand (fine and coarse) of the same mineralogy, with a Sand/Cement ratio of 3 and a Water/Cement ratio of 0.5. The samples were subjected to five temperature levels: 20, 100, 150, 200, and 250°C. After cooling down to ambient temperature, several properties were measured, including mass loss, dimensional changes, bulk density, water absorption by immersion (total porosity), water absorption by capillarity, and compressive strengths. The results reveal a systematic influence of particle size: mortars made with fine sands exhibit a higher mass loss and consistently lower compressive strengths than those made with coarse sands, regardless of the applied temperature. In terms of hydric durability, fine sand mortars show lower water absorption by immersion (lower total porosity) but a higher absorption by capillarity, which indicates a microstructure characterized by finer but more interconnected pores, thereby favoring micro-cracking under thermal stress. In conclusion, the study demonstrates that sand particle size is a determining factor in the post-thermal performance of mortars, and the use of coarse sands is preferable to ensure better mechanical stability and increased resilience for structures exposed to temperatures up to 250°C.