Study on strength and durability aspects of flyash aggregate concrete

Abstract

Fly ash is a residue left after burning of coal in thermal power stations and need suitable disposal system so that it does not become hazardous and injurious to human life and environment. Besides the use of fly ash as partial replacement material, its use as aggregate in concrete can pave the way for large scale use of fine aggregate. Most of the previous research works were done by using conventional fine and coarse aggregates in concrete. In this research work, the fine and coarse aggregates were completely replaced by fly ash aggregates in concrete. Mix design was done for M20 grade of concrete by IS method. The design of fly ash aggregate concrete mix based on the extensive experimental investigations at the Building Research Station UK was followed to design the mix proportions for fly ash aggregate concrete. Ordinary Portland cement of 43 grade was selected and fly ash aggregates were prepared by mixing fly ash with 43 grade cement. The fly ash aggregates were sieved and the aggregates having size less than 4.75mm were taken as fly ash fine aggregate and above 4.75mm to 20mm were taken as fly ash coarse aggregate. 20mm size fly ash aggregates were sieved separately and used as fly ash coarse aggregate for the experimental work. The properties of fly ash fine aggregates and fly ash coarse aggregates were determined. The aggregate crushing value and aggregate impact value of fly ash coarse aggregates were also determined. The cement and fly ash proportions of 10:90, 12.5:87.5, 15:85, 17.5:82.5, 20:80 and 22.5:72.5 were adopted with a suitable water cement ratio 0.3 to prepare the fly ash aggregates. The method of formation of fly ash aggregates is called Pelletisation. The concrete cubes, cylinders and beams were cast with the fly ash aggregates obtained from the above six cement fly ash proportions. Then the cube compressive strength, split tensile strength, flexural strength and cylinder compressive strength tests were conducted at different ages