XRD and TGA, Swelling and Compacted Properties of Polymer Treated Sulfate Contaminated CL Soil

In this study, the effect of up to 4 % calcium sulfate contamination on the soil properties of a natural clay with low liquid limit (CL) soil with and without polymer treatment was investigated and compared to 6 % lime treated soil. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) methods were used to identify and quantify the changes in the contaminated CL clay soil. XRD analyses showed the major constituents of the soil were calcium silicate (CaSiO₃), aluminum silicate (Al₂SiO₅), magnesium silicate (MgSiO₃), and quartz (SiO₂). With 4 % calcium sulfate contamination, the liquid limit (LL) and plasticity index (PI) of the CL soil increased by 30 and 45 %, respectively. The addition of calcium sulfate resulted in the formation of calcium silicate sulfate (Ternesite Ca₅(SiO₄)₂SO₄) and aluminum silicate sulfate (Al₅(SiO₄)₂SO₄). TGA analyses showed a notable reduction in the weight of calcium sulfate contaminated soil between 600 and 800°C, possibly due to changes in soil mineralogy. In addition, the total weight loss at 800°C for 1.5 % polymer treated soil was about 40 % less than the 4 % calcium sulfate contaminated soil, and it was similar to the weight loss observed in the uncontaminated CL soil. The maximum dry density of compacted soil decreased and the optimum moisture content increased with 4 % of calcium sulfate. The addition of 4 % calcium sulfate increased the free swelling of compacted soil by 67 %. The addition of 6 % lime resulted in the formation of ettringite (Ca₆Al₂ (SO₄)₃(OH)₁₂·26H₂O). Polymer treatment decreased the LL, PI, swelling index, and optimum moisture content of the soil and increased the compacted maximum dry density. Behavior of sulfate contaminated CL soil with and without treatment was quantified using a unique model that represented both linear and nonlinear responses. Also the model predictions were compared with published data in the literature.