Fly ash to control alkali-induced volume changes in soils

Abstract

It is known that alkali contamination can alter the engineering behaviour of soils to varying extents, depending on the soil type, the alkali concentration and the duration of interaction. This paper presents the effect of 2m sodium hydroxide solution on the swelling and compressibility of black cotton soil possessing interstratified mineral and red earth with predominant kaolinite clay mineral, studied by means of detailed consolidation tests. It has been shown that an increase in swelling and a decrease in compressibility of the soils occur as a result of contamination with 2m sodium hydroxide solution. The observed swelling is greater for black cotton soil containing mixed layer mineral than for kaolinitic red earth. Also, the swelling in black cotton soil contaminated with alkali occurs in two stages. This has been attributed to mineralogical changes leading to the formation of different forms of zeolite. The effectiveness of fly ash, which is not affected by alkali, in reducing alkali-induced effects is studied in this paper. Fly ash, when included in soil at concentrations of 25–50%, effectively controls alkali-induced swelling in soils by preventing the formation of new zeolite minerals.