Flexural Performance and Energy Absorption of Reinforced Concrete Beams Incorporating Rice Husk Ash under Normal and Acidic Environments

This study investigates the flexural behavior and energy absorption of reinforced concrete beams incorporating rice husk ash (RHA) under normal and acidic environments (pH 3). Six beam specimens were cast with RHA replacement levels of 0%, 5%, and 10% and tested under four-point bending. The experimental variables included initial cracking load, yielding load, ultimate load, mid-span deflection, and total energy absorption based on the load–deflection response. The results indicated that beams with 5% RHA exhibited the best performance in both environments, with significant improvements in flexural strength, cracking resistance, and deformation capacity. Under acidic conditions, RHA-modified beams demonstrated higher resistance to degradation, attributed to the pozzolanic reaction that enhanced the microstructure and reduced porosity. Energy absorption analysis revealed that 5% RHA beams achieved over 2.3 times the reference value in normal water and nearly twice under acid exposure. Meanwhile, 10% RHA beams showed moderate improvements, suggesting a diminishing return at higher replacement levels. The study also found that RHA enhances ductility, although it increases mid-span deflection, which should be considered in structural design. These findings support the use of RHA as a sustainable partial cement replacement, especially for structures exposed to chemically aggressive environments. The outcomes of this research offer practical guidance for optimizing material selection and structural performance in the development of durable and environmentally resilient concrete infrastructure.