Effect of Rice Husk Ash Addition on Durability Properties of Mortars

Prismatic mortar specimens with dimensions of 40 × 40 × 160 mm were produced in accordance with TS EN 196-1:2016 using rice husk ash (RHA) as a partial cement replacement at levels ranging from 0% to 15%. The specimens were exposed to aggressive seawater and 7% NaCl environments and evaluated through compressive strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption, carbonation, capillary water absorption, and thermal conductivity tests. The highest compressive strength values were generally obtained at RHA replacement levels of 8–10%, depending on the exposure condition and curing period. In the 7% NaCl environment, most RHA-incorporated mixtures exhibited higher flexural strength than the control mixture, with the highest values generally observed at replacement levels between 6% and 10%. UPV results indicated that the incorporation of RHA did not significantly impair the internal quality of the mortars. Water absorption, capillary water absorption, and carbonation depth generally increased with increasing RHA content, particularly at replacement levels of 10–15%. No carbonation depth was observed in the control specimens, whereas the highest carbonation depths were measured in the 15% RHA mixtures. Thermal conductivity decreased with increasing RHA content, with the lowest values obtained at the highest replacement levels. Overall, the results indicate that RHA replacement levels of approximately 8–10% provide a favorable balance between mechanical performance, durability-related properties, and thermal insulation performance under aggressive chloride-rich exposure conditions.