Modeling the effect of chemical additives on clay soil plasticity: novel analysis of oxide contributions in fly ash and cement treatments

Soil comprises the five primary chemical oxides: silica, alumina, calcium, magnesia, and ferric. The proportions of these oxides significantly influence the geotechnical characteristics of soil. In addition, certain soils can be modified by using chemical additions such as fly ash and cement. These additives lower the plasticity of the soil and effectively mitigate swelling, allowing for better control over soil characteristics. The fly ash and cement both include a significant amount of the specified oxides. Modifying the soil-additive matrix by combining or increasing the proportion of one or two oxides could greatly enhance geotechnical characteristics, namely plasticity parameters. This study compiled a total of 240 datasets, consisting of 139 datasets of untreated soil and 57 and 44 datasets for fly ash and cement-treated soil, respectively. The impact of fly ash and cement on the plasticity parameters was examined, revealing that adding fly ash and cement at an optimal level can decrease both the liquid limit and the plasticity index. Next, the impact of the primary chemical oxides on the liquid limit (LL) and plasticity index (PI) was demonstrated in both untreated and additive-treated soil. Subsequently, four distinct multivariable mathematical models demonstrated the occurrence of both LL and PI to CaO, SiO₂, Al₂O₃, MgO, and Fe₂O₃. The study demonstrated that a highly intricate connection may be achieved using a polynomial regression model to predict the LL and PI based on the primary oxides for untreated, cement-treated, and fly ash-treated samples. The model yielded an R² value of 0.8, indicating a strong fit. Regarding sensitivity analysis, SiO₂ had the greatest impact on both LL and PI, followed by Fe₂O₃.