Density Performance of Eco-Friendly Hollow Concrete Blocks with Wood Sawdust as a Sustainable Partial Replacement for Sand

This study evaluated the density performance of eco-friendly hollow concrete blocks incorporating wood sawdust as a partial replacement for sand, using four mix ratios (1:2:0.3, 1:1.5:0.4, 1:1:0.5, and 1:0.5:0.7) and replacement levels of 0%, 5%, 10%, and 15% by weight. Blocks (150 × 225 × 450 mm) were fabricated with Ordinary Portland Cement, river sand, and sieved sawdust (≤ 2 mm), cured for 28 days, and tested in accordance with ASTM standards. Results showed that dry density decreased significantly (p < 0.05) with increasing sawdust content across all mixes; for instance, in the 1:2:0.3 ratio, it ranged from 2,436.67 ± 30.55 kg/m3 (0%) to 1,963.33 ± 98.15 kg/m3 (15%). Wet density at 24 hours and 48 hours followed similar downward trends, with richer cement mixes (e.g., 1:1:0.5) maintaining higher density values. The reductions are attributed to sawdust’s lower bulk density (150–300 kg/m3) and increased porosity within the block matrix. These results highlight that 5%–10% sawdust replacement provides notable reductions in density, producing lighter blocks that may be advantageous for handling and thermal efficiency. However, density performance alone cannot determine structural or durability suitability. Further studies on compressive strength, water absorption, and long-term durability are needed to establish the full potential of sawdust-modified hollow blocks for construction applications.