Effect of sand particle size on the thermal effusivity of clay-admixed cement mortar bricks

Improving the thermal properties of cement mortar bricks incorporating clay while maintaining constant mass remains a significant challenge in construction engineering. This study investigates the impact of sand granulometry on the thermal properties of cement mortar bricks incorporating clay as a partial sand replacement. Three sand size classes E₂ (0.08/0.5), E₃ (0.5/1.6), and E₄ (1.6/2) were examined. Clay and sand were characterized in accordance with standards NF P94-051 and NF P94-041. Sand was replaced by clay at rates ranging from 0 to 60% of the total sand mass, corresponding to clay contents of up to 45%. Thermal measurements were performed on 63 samples using the asymmetric hot plate and parallel hot wire methods. Specimens were cast in standard molds with dimensions of 100 × 100 × 30 mm3. For all granulometries, thermal effusivity and conductivity decreased with increasing clay content. Maximum reductions in effusivity and conductivity were 18.37% and 33.9% for E₂, 25.55% and 43.6% for E₃, and 27.76% and 43.8% for E₄, respectively. At constant clay content, finer sand resulted in lower thermal properties, whereas coarser sand led to higher values. Optimizing sand granulometry therefore appears to be an effective strategy for enhancing indoor thermal comfort in residential buildings.