Alternative calcium-based chemical stabilisers for ground improvement: Paper Sludge Ash treatment of London Clay

Due to the recent focus on promoting sustainable construction practices, chemical ground improvement of problematic soils for construction has been increasingly used worldwide. However conventional soil stabilisers such as cement or lime still suffer from the use of nonrenewable natural resources, high energy consumption and CO2 emissions for their production. Consequently alternative stabilisers are intensively sought; these would be linked to lower or even zero CO2 emissions if these come from waste. The paper studies the effect of waste paper sludge ash (PSA) as an alternative to lime for the treatment of London clay (a moderately expansive soil). The effectiveness of the treatment is assessed comparing a number of PSA-treated soil properties (plasticity characteristics, unconfined compressive strength and stiffness) to those of the same soil treated with lime. In most cases the PSA-treated soil specimens are shown to have a better performance than the lime-treated ones. The findings on the macroscopic properties are complemented by microstructural analysis.