<![CDATA[The utilization of Rice Husk Ash (RHA) as a supplementary cementitious material (SCM) in Portland Composite Cement (PCC) mortar offers a sustainable approach to reducing cement consumption, mitigating CO₂ emissions, and valorizing agricultural waste. However, the effectiveness of RHA is influenced by the curing regime, which governs hydration and pozzolanic reactions, thereby affecting the microstructure and mechanical performance of mortar. This study investigates the influence of RHA substitution and curing methods on the mechanical properties and microstructure of PCC mortar. Mortar specimens were prepared with RHA replacement levels of 0%, 10%, and 20% by weight of cement and cured under water curing and air curing conditions. Fresh mortar workability, compressive strength, flexural strength, and microstructural characteristics were evaluated using Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The results indicate that increasing RHA content reduced mortar workability; therefore, superplasticizer dosages of 1.0% and 1.5% were incorporated to maintain adequate consistency. At 28 days, 10% RHA under air curing reduced compressive strength by approximately 2% relative to the control mixture, whereas 20% RHA reduced it by 20%. In contrast, water curing with 10% RHA enhanced compressive strength by approximately 2%, while 20% RHA showed no improvement over the control. Flexural strength decreased under both curing regimes as the RHA replacement level increased. SEM and FTIR results indicated that water curing promoted a denser microstructure and increased hydration product formation at 10% RHA replacement, leading to improved mechanical properties relative to specimens subjected to air curing]]>
