Swell and compressibility of fly ash−clay blends in lumps and powders: effect of 4% lime

Abstract

This paper describes the influence of fly ash on the swell-compressibility characteristics of an expansive clay passing through a 4·75 mm sieve. The free-swell index (FSI), heave, swell potential, swelling pressure, coefficient of compressibility (av), the compression index (Cc) and linear shrinkage (LS) of fly ash–clay blends were studied. Fly ash content was varied from 0, 5, 10, 15 to 20%. Swelling and compressibility of the clay decreased with increasing fly ash content. Heave was the lowest at 15% fly ash. The paper compares the effect of 15% fly ash on the swell-compressibility behaviour of clay lumps passing a 4·75 mm sieve and clay powder passing a 425 μm sieve. While the swell potential was found to be higher for clay powder than for clay lumps at 15% fly ash, the swelling pressure was higher for clay lumps. As 4% lime resulted in the highest reduction of the FSI, a series of swell-consolidation tests and a series of FSI tests were conducted on fly ash–clay blends to which 4% lime was added. FSI, heave and swelling pressure decreased on the addition of fly ash. They further decreased when 4% lime was added. The parameters av, Cc and LS also reflected a similar trend.