Additives based on vegetable biomass to improve the stabilisation of expansive clay soil

Abstract

This paper investigates the effect of different bio-based additives on the expansiveness of an Argentinian natural clayey soil (CR-clay). CR-clay was characterised to determine (a) the Atterberg parameters and other index properties, (b) the particle size distribution by laser diffraction, (c) the specific surface area (Se) and cationic exchange capacity by the methylene blue method, (d) the mineralogy by using X-ray diffraction, (e) the functional groups by Fourier transform infrared spectroscopy (FTIR) and (f) the free swelling and swelling pressure by using an odometer. Starches from potato, cassava, corn and rice flour; seeds and derivatives from flax, sunflower and quinoa; kraft lignin; and lignosulfonates were evaluated as soil stabilisation additives on the basis of measurements of Atterberg parameters. Reductions in the soil plasticity index (PI) between 10 and 60% were generally observed. Lignins exhibited a very good balance between the ability to improve soil stabilisation, low costs, environment-friendliness and availability. In particular, kraft lignin showed high performance as a CR-clay stabiliser with a PI reduction of 46%. The stabilisation mechanism of lignin and CR-clay blends was investigated using Z potential and FTIR. Based on the experimental results, lignins constitute promising alternatives to the additives used as stabilisers of expansive soils, particularly for reducing free-swell and swelling pressure.