ADDITION OF FLY ASH IN SMALL QUANTITY TO CONCRETE: EFFECTS ON STRENGTH, WORKABILITY AND WATER ABSORPTION

Abstract

Fly ash has been in use for decades, since 1930s, as partial replacement for cement in concrete production, thereby serving a dual purpose of safe disposal of coal ash and reduction in cost of concrete manufacture ,but its use as admixture(addition in small quantity) is yet to be  appreciated. Coal is still the world’s favorite fuel for electricity generation, and this suggests increase in fly ash production worldwide in the near future. There is therefore the need to increase fly ash utilization. In this regard this paper studied addition of fly ash as admixture to concrete and its effects on the strength, workability and water absorption properties of concrete. Concrete cubes of mix ratio 1:2:4 and water- to-binder ratio of 0.58 were prepared with fly ash contents of 0%, 2%, 4%, 6%, 8%, 10%, 13%, 16%, 20% and 50%. Compressive strength, workability and water absorption tests were conducted on the respective concrete cube specimens. It was observed that the strength and workability of the concretes improved appreciably, and increased with increase in fly ash content with a maximum at 20% fly ash content. Water tightness was highest at 13% content. Fly ash was therefore recommended as admixture for concrete to improve strength and workability of concrete and to be added at 2% to 20% by weight of the cement content, when casting thin walled sections and congested reinforcement sections. It was also recommended to be used at 13% by weight of the cement content to ensure water tightness in aggressive environments.            

 

KEYWORDS: fly ash, concrete, admixture, compressive strength, workability, water absorption, fly ash utilization