Ashes of Biogenic Wastes—Pozzolanicity, Prospects for Use, and Effects on Some Engineering Properties of Concrete

The growing concern for the environment all over the world, as well as the high cost of Portland cement has placed limitation on its use as the sole binding material in concrete. This work has shown that ashes from some agricultural or other biogenic wastes when mixed with appropriate amounts of ordinary Portland cement (OPC) can be used as low-cost, environmentally, more friendly binders for concrete production, than using OPC alone. Experimental determination of requisite properties of the ashes of rice husk, coconut husk, palm leaf, bamboo leaf and peanut shell revealed that they satisfy the essential requirements for pozzolans. Further experimental work was carried out on OPC/rice husk ash (RHA) and OPC/coconut husk ash (CHA) concretes to determine their essential properties in fresh and hardened states. Although the initial and final setting times of OPC/RHA and OPC/CHA pastes were longer than the setting times of 100% OPC paste, they are all within the limits specified by relevant standards. The workability of fresh concrete produced by partially replacing OPC with either of RHA and CHA was found to be better than with 100% OPC. It was also shown that the porosity of OPC/RHA and OPC/CHA concretes was less than the porosity of OPC concrete. Strength tests using very finely ground RHA and CHA to partially replace Portland cement in concrete production showed that at up to 15% replacement the strength activity index of each of them is greater than 100%, which indicating that they are excellent pozzolans.