Utilization of Ashes of Some Agricultural Wastes in Concrete: Effect on Strength and Transport Properties

Abstract

In this study, rice husk ash (RHA) and saw dust ash (SDA) were mixed with Portland limestone cement (PLC) in various proportions to produce concretes having 28-day target strength of 30 MPa. Four mixes were utilized in the study – a plain mix containing only PLC and three ternary blends containing 80% PLC and 20% of RHA and SDA in varying proportions of 15% RHA + 5% SDA, 10% RHA + 10% SDA and 5% RHA + 15% SDA. Concrete cubes were prepared from these mixes and cured for 3, 7, 28, 56 and 90 days. Various tests including consistency, initial and final setting time, compressive strength, and water absorption were conducted. The results showed that the addition of RHA and SDA to PLC resulted in an increase in the consistency, initial and final setting times of the cement paste. This was attributed to the hygroscopic nature of the ashes and their high specific surface area making them to demand more water. The compressive strengths of the ternary blends were seen to be lower than that of the plain mix at all ages. The water absorption test result showed that more water was absorbed by the concrete samples prepared from the mixes containing blends of RHA and SDA, as compared to those prepared from the plain mix. Overall, the ternary blends had inferior performance as compared to the plain mix. It was also observed that the performance of the ternary blends worsened as the RHA content decreased