A comparative assessment of alkali-activated stabilisers including waste materials, for the treatment of swelling-shrinking soils

Swelling-shrinking soils (also known as expansive soils) experience very considerable volume changes upon changes in moisture content, thus causing major damages to lightweight structures, pavements, slopes and utilities. To counteract this problem chemical stabilisation of this type of soil with agents such as lime has been extensively used. However, the production of lime causes high CO2 emissions. Thus, there are intensive efforts in finding alternative stabilisers of lower carbon footprint. In this context, alkali-activated cements (AAC) show potential in becoming more sustainable alternatives to conventional soil stabilisers. The aim of this study was to assess the performance of a number of AAC systems as stabilisers of a swelling-shrinking clay soil. Activators of ground-granulated blast-furnace slag also included a waste material (Paper Sludge Ash, PSA) used as a source of calcium oxide. All studied AAC mixes reduced considerably the propensity of the soil to swell in the presence of water. Potassium-based AAC binders were most effective in reducing the soil plasticity and also reduced other swelling indices reflecting an improved volumetric stability of the soil. PSA showed consistently good performance and is therefore a promising activator to study further.