Mitigation of the Swelling Behavior of Expansive Soils Using Hydrophobic Lignosulfonate: Adsorption Mechanism

Expansive soils exhibit shrink-swell characteristics due to the presence of clay mineral constituent. Often such soils are stabilized using chemical stabilizers. This study examined the potential application of calcium-based lignosulfonate (LS), a by-product chemical of the pulp industry, in stabilizing expansive soils. Soils with various grain-size distributions and degrees of expansivity were chosen to investigate the efficacy of the chemical treatment. The lignosulfonate was mixed with the chosen soils in different dosages to obtain the optimum dosage of the chemical. The effect of chemical dosage on the grain-size fractions, Atterberg limits, percentage swell, swell potential, and swell-consolidation characteristics of expansive soils were assessed. The influence of chemical dosage and curing period on the evolution of the new mineral phases, microfabrics, and soil structure were investigated. The results indicate the necessity of fixing the optimum dosage of lignosulfonate for different soils. The lignosulfonate addition decreased the swelling characteristics of the chosen expansive soils. The expansive soils rich in silt fraction had a reduction in plasticity and swelling characteristics up to the optimum dosage of LS, but a trend reversal beyond the optimum dosage, which can be attributed to the formation of a high percentage of silicates. In contrast, soils rich in montmorillonite mineral had a significant reduction in plasticity and swelling characteristics up to the optimum LS dosage, beyond which there was a negligible reduction without trend reversal. The possible mechanisms of LS-treated expansive soils in enhancing the engineering properties of expansive soils are addressed.