Typical XRD patterns of the stabilized soils for Mix-1 and Mix-2 at 3 and 90 days curing time Figure 14 to Figure 17, showed growths of major reaction products which could be identified as CSH and ettringite. As obviously seen in Figures 18 and 19, X-ray intensities of CSH products and ettringite for all mixtures illustrated their formations similar to strength characteristic curves. In addition, the developed strength exhibited general trend to increase proportionally with amounts of CSH and ettringite. This can be observed as shown in Figure 20 and Figure 21. In essence, the higher reflections were obtained from the mixtures having relatively higher strength. It could therefore be concluded that these reaction products mainly contribute to strength development of the stabilized soils.
Another essential role of ettringite (3CaO.Al2O3.3CaSO4.32H2O) was attributed to the fact that large amount of water was combined in its crystals, resulting in significant decrease in moisture content at the early age. Extracting water that existed in the pore spaces by ettringite provided a reduced water to cement ratio that aided further hardening. The previous works done by Ariizumi et al. (1977) and Kamon et al. (1989) assumed that the formation of ettringite significantly improved the leachate characteristics of the stabilized soil by combining metallic ion such as Fe 3+ or heavy metal such as Cr 3+, and fixing them in its crystal. Based on the environmental geotechnical viewpoint, this confirmed the potential uses of the fly ash from vegetable oil factory combined with cement to stabilize soft marine clay.