Effect of Green Admixtures on the Mechanical Properties of Concrete Composite

The study was carried out to evaluate the suitability of organic admixture in concrete production. Six sets of concrete were made by partially replacing the fine aggregates (sand) and coarse aggregates (gravel) with 0, 5, 10, 15, 20 and 25% of sawdust and periwinkle shells respectively, in the presence of 0, 0.5, 1, 1.5, 2 and 2.5% cassava starch. The compressive strength and density of the six concrete groups were tested, in accordance with American Society for Testing and Materials (ASTM) International approved guidelines. Findings from the laboratory investigations indicated that the sawdust and periwinkle admixtures generally reduced the concrete compressive strength, as their proportion in the concrete increased from 0 to 25%; while the cassava tends to increase the concrete’s compressive strength. The compressive strength of the concrete declined from 25.2 to 10.3 MPa, 27.1 to 11.7 MPa, 30.7 to 13.6 MPa, 31.4 to 14.5 MPa, 30.9 to 14.2 MPa, and 28.4 to 13.8 MPa, after the incorporation of 25% sawdust and 25% periwinkle shells, as partial replacement for sand and gravels respectively, in the presence of 2.5% cassava starch. Furthermore, the results revealed that the compressive strength of the concrete increased non-linearly, as the cassava starch volume increased from 0 to 2.5%. However, the concrete set produced from 20% sawdust and 20% periwinkle shells was light-weight and its compressive strength was within the limit of 17 MPa recommended by Nigeria Industrial Standard (NIS) for light-weight concrete required for residential buildings construction. The findings of this study revealed that agricultural waste materials are suitable admixture materials in the concrete industry.