Effects of Relative Humidity on the Mechanical Properties of Rice Husk Ash Concrete

This study investigates the influence of environmental relative humidity (RH) on the mechanical properties and durability behaviour of rice husk ash (RHA) concrete. Concrete cubes were produced with 0%, 5%, 10%, and 15% RHA as partial replacement for Portland limestone cement and cured under three simulated RH conditions (31%, 51%, and 78%) representing typical Nigerian climates. Each test—compressive strength, ultrasonic pulse velocity (UPV), and water absorption—was conducted in triplicate at curing ages of 7, 14, 28, and 91 days. Statistical analysis (ANOVA) and error bars were used to establish the significance of RH levels and RHA percentages. Results show that 5% RHA at 78% RH achieved optimal performance, meeting the Grade 25 concrete target. Strength and UPV decreased at lower RH levels and with higher RHA percentages. Water absorption increased with RHA content, especially under 78% RH. These findings provide valuable insights for construction in tropical climates and promote sustainable use of cement through RHA utilization.