Variation of OPC-Rice Husk Ash-Saw Dust Ash Composites Strength with Mix Proportion

This work investigated the variation of strength of OPC-RHA-SDA cement composites with mix proportion. 168 concrete cubes of 150mm x 150mm x 150mmwere produced with OPC and RHA-SDAusing percentage OPC replacement with RHA-SDA of 0%, 10%, 15%, and 20%, and sevenwater: blended cement: sand: granite mix proportions of 0.6:1:1.5:3, 0.6:1:2:3, 0.6:1:2:4, 0.7:1:2.5:4, 0.7:1:2.5:5, 0.7:1:3:5, and 0.7:1:3:6.168 sandcrete cubes and 168 soilcrete cubes were also produced using the same percentage replacements and water: blended cement: sand (or laterite for soilcrete) mix proportions 0.6:1:4, 0.6:1:5, 0.6:1:6, 0.7:1:7, 0.7:1:8, 0.7:1:9, and 0.7:1:10.Three concrete, sandcrete, and soilcretecubes for each percentage OPC replacement with RHA-SDA and mix proportion were crushed to obtain their compressive strengths at 28 and 50 days of curing. It was found that for all percentage replacements of OPC with RHA-SDA at 28 and 50 days of curing, at a given water/cement ratio, the compressive strengths increased with leanness of mix up to some level of leanness after which the strength reduced. Concrete compressive strength values for 20% RHA-SDA at 50 days of curing rose from 20.60N/mm2 for 0.7:1:2.5:4 mix, to 21.20N/mm2 for 0.7:1:2.5:5, to 22.10N/mm2 for 0.7:1:3:5, and decreased to 21.60N/mm2 for 0.7:1:3:6. These results suggest that the leanest mix proportions that would still allow for good compaction should be used in making OPC-RHA-SDA cement composites for optimum compressive strength and cost effectiveness.