Evaluation of strength development and micro-pore characteristics of stabilized expansive soil

In the present study, the influence of multiple additives on the strength development and micro-pore characteristics of a weak expansive soil, known as tropical black clay (TBC), was investigated. The multiple additives, which included rice husk ash (RHA), quarry dust (QD) and Portland limestone cement (PLC), were added in different percentages to the TBC by its air-dried weight with mix ratios generated from Taguchi mixed level L9 orthogonal. Thereafter, geotechnical properties such as unconfined compressive strength (UCS), California bearing ratio (CBR) and differential free swell (DFS) of the natural TBC and that of the TBC that were blended with the multi-additives were assessed after subjecting them to several curing days. The optimum combination of the additives that resulted in optimal values of the assessed geotechnical properties was obtained as 15% RHA + 10% QD + 6% PLC. Furthermore, evaluation and quantification of the micro-pore characteristics (porosity and pore size distribution) of the scanning electron microscopy (SEM) of the natural TBC and that of the TBC that was blended with the optimum combination of additives and cured for 7 and 28 days were executed with two image segmentation analysis (Otsu thresholding and local adaptive thresholding). The results obtained from the analysis revealed that the combination of the natural TBC and the multiple additives significantly improved the UCS, the CBR and the DFS of the TBC. The significant improvement was attributed to the filling of the natural TBC voids by the QD and the interplay between the pozzolanic and hydration reactions experienced within the TBC-additives matrix. In addition, the result from the analysis of the SEM images showed a noticeable reduction in the micro-pore characteristics of the samples blended with the optimum combination of additives as its days of curing increases.