Performance of different chemical soil stabilisers in the presence of sulphates

Ground improvement of sulphate-bearing soils with calcium-based stabilisers can be severely compromised due to delayed deleterious reactions of the sulphates with calcium, and the consequent formation of expansive crystals of minerals such as ettringite or thaumasite. Amongst other ways to prevent this or mitigate the effects, the literature recommended the use of slags and pozzolanic industrial by-products to replace partially calcium-based stabilisers. This study is thus focusing on assessing whether suitable combinations of such materials partially or fully replacing calcium lime could effectively stabilise sulphate-bearing soils. In addition, the use of magnesium-based additives instead the calcium-based ones is investigated. The added advantage of using these materials is that they are more environmentally friendly than Ordinary Portland Cement and calcium lime, whose production involves high energy input and CO2 emissions. An artificial sulphate bearing soil was treated with mixtures of lime, paper sludge ash (PSA), pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS) and reactive magnesia cement. Using favourable conditions for the formation of sulphate-induced swelling, compacted soil samples were created and subjected to moisture ingress after 7 and 28 days of curing respectively. Following this, the swelling of the specimens was monitored, and their unconfined compressive strength (UCS) measured. It was found that, although some binder combinations were more successful and showed promise, no binder mix was fully successful in preventing the damage of the samples and suppressing swelling fully. More research is required leading to precise specifications, so that such stabiliser mixes can be used in industrial applications with confidence.