Abstract
This study investigates the combined use of rice husk (RH) as an organic lightweight filler and rice husk ash (RHA) as a partial Portland-cement replacement in arbolite composites. Six mixtures containing 0–20% RHA were prepared at a constant total binder content and water-to-binder ratio. Density, compressive and flexural strength, water absorption, freeze–thaw resistance, and microstructural features were evaluated. Each physical and mechanical property was determined using three specimens, and the results were processed using the arithmetic mean, standard deviation, and coefficient of variation. The optimum mixture containing 12.5% RHA reached a compressive strength of 3.8 MPa and a flexural strength of 1.8 MPa, representing increases of 26.7% and 80%, respectively, relative to the RHA-free control. Water absorption decreased from 21.5% to 17.2%. After 35 freeze–thaw cycles, the optimum mixture retained a frost-resistance coefficient of 0.65, whereas the control specimens lost structural integrity. Microscopy revealed relatively compact binder-matrix regions in the optimized composition, consistent with the measured performance trends. The scientific novelty lies in determining an RHA dosage that simultaneously balances density, strength, water absorption, and freeze–thaw resistance in rice-husk-based arbolite. The developed material is recommended for non-load-bearing wall and partition elements, provided that appropriate moisture-protective finishing is used.