Effect of freeze–thaw cycles on the strength and physical properties of cement-stabilised soil containing recycled bassanite and coal ash

Abstract

Earth materials deteriorate physically under freeze–thaw cycling. It is thus important to determine how freeze–thaw cycling affects their properties of new man-made materials in areas experiencing seasonal frost. The effect of variable freeze–thaw cycling on the durability of cement-stabilised soils containing bassanite and coal ash was quantified to promote the use of bassanite in earthwork project in seasonal frost areas. For this purpose, very soft clay was stabilised with 5% cement content by weight of dry soil, and bassanite and coal ash were mixed with it in differing proportions. These stabilised soil samples were subjected to differing numbers of freeze–thaw cycles (up to five cycles), after curing for 28days. Unconfined compressive strength and several physical properties were investigated after freeze–thaw cycling. The results show that the addition of both bassanite and coal ash improves the strength and durability of stabilised soils significantly, whereas the addition of coal ash alone has a negative effect on strength improvement. Unconfined compressive strength increases with increased bassanite and coal ash contents. With respect to freezing and thawing durability, the first or second cycles of freeze–thaw action markedly decrease the unconfined compressive strength of both treated and untreated cement-stabilised soils, but further cycles have little additional influence. The use of both additives improves durability, and retains 65–85% strength compared to corresponding non-frozen stabilised soils; if either additive is used, the strength is 55–65%; and if no additives are used, about 50%. The effects of freeze–thaw cycling on water content and dry density are negligible compared to those of additive contents. Volume after freezing increased slightly with increase in the number of freeze–thaw cycles, although volume after thawing fell slightly and reached minimum at the first thawing process.