Potential use of phosphogypsum as an additive for stabilizing soft kaolinite soils: enhancement of the foundation layer

The shear resistance of clayey soils can be improved through chemical stabilization with hydraulic lime. This study examines the stabilization of soft kaolin clayey soils by adding phosphogypsum (PG) waste and lime. This approach reuse of PG waste, typically stored in piles, by integrating it into kaolin-rich soils to improve their stability. Structural, microscopic, geotechnical, and mechanical characterization techniques were employed to enhance the understanding of soil stabilization mechanisms and their potential applications in road construction. Kaolinite lacks pozzolanic reactivity with lime, but crystalline and amorphous aluminosilicates in the soil facilitate the formation of calcium silicate hydrate (CSH) gel, which binds soil particles cohesively. The addition of PG to the soil-lime mixture allows soil stabilization through the formation of ettringite and CSH gel, and the crystalline needle-like of phosphogypsum. The mechanical compressive strength increases from 0.35 MPa for raw earth mortar consisting of 90% soil and 10% lime to 0.80 MPa for a mixture consisting of 68% soil, 10% lime and 32% PG. The compressive mechanical strength obtained by adding PG to kaolin clay exceeds the minimum threshold of 0.66 MPa required for the structural design of road pavements.