Soil-lime reaction and microstructural development at elevated temperatures

Abstract

Mineralogical analysis of Devonian Red Marl using XRD, TEM, SEM and EDAX showed that it consisted of illite, quartz, and feldspar with minor amounts of chlorite and hematite. Physico-chemical changes in the soil minerals on reaction with lime (calcium hydroxide) from one day up to two years were investigated by these techniques to gain information on the soil-lime reaction mechanism. Significant reaction of the soil minerals and lime was found to occur only at elevated temperatures (50–75°C) in a moist environment. At these temperatures, formation, growth and development of fibrous and foil-like cementitious material was observed. XRD analysis provided no strong evidence for the formation of new phases. TEM analysis and EDAX, however, showed that the newly-formed fibrous and foil-like material consisted of an amorphous calcium silicate aluminate hydrate gel, similar to the gels formed during hydrothermal treatment of lime-silica, but with lower calcium to silicon ratios than previously reported for such gels. The morphological development of the gel suggested that it formed as a result of the progressive breakdown of the clay component in the soil by reaction with the calcium ions from the lime.