Response surface methodology: a tool to optimise the contents of lime and polyethylene terephthalate (PET) fiber for stabilising a residual soil

ABSTRACT The possibility of stabilising a residual soil using lime and polyethylene terephthalate (PET) fibre by employing the central composite design technique in response surface methodology and using the desirability function to identify optimum additive combinations for the improvement in the strength properties of the treated soil was explored in this study. The effects of the independent variables (lime content, PET content, and curing duration) on the responses [unconfined compressive strength (UCS) and flexural strength (FS)] were investigated by analysis of variance (ANOVA). The results indicate that the developed mathematical models are statistically significant (p ≤ 0.05) through the analysis of variance, thus they are applicable for the optimisation process. Predicted values from the developed models were found to be in good agreement with their experimental counterparts. The optimum conditions were found to be 9% lime content, 1.9% PET fibre content, and 30 days curing duration, with a designated maximum desirability function (D = 0.996). Microstructural investigations revealed that the formation of calcium-aluminate-hydrate and calcium-silicate-hydrate were the key components liable for the improvement in the strength properties of the treated soil. The reported findings engaged the concurrent application of lime and PET fibre to improve the strength properties of residual soils.