Ettringite formation and behaviour in clayey soils

Failures in soil stabilization have been reported previously as being due to the formation of ettringite, an expansive mineral which develops in the presence of sulfate, calcium, and aluminum compounds of clay fraction in high pH levels between 10.36 and 14. By comparing the pattern of formation of ettringite, formed from different possible sources and specifically in stabilized soil, it is expected that a clearer picture of the kinetics of ettringite formation from different sources will be obtained. In this paper, a set of physico-chemical experiments and XRD tests were performed to investigate the process of ettringite formation and to explore its possible performance in clayey soils. The growth of the ettringite XRD peaks was used as a measure of the rate and its formation pattern. It is shown that the rate of ettringite formation in soil stabilization is much slower than that of artificial ettringite. Furthermore, it is shown that ettringite swells to the order of 50% and its fluid retention is significantly higher (by as much as 400%) than that of the soil sample studied in this research.