Biocementation of calcareous sand using soluble calcium derived from calcareous sand

Abstract

A soil improvement method based on a microbially induced carbonate precipitation (MICP) process has been developed in recent years. In this method, calcium carbonate is precipitated in-situ to act as a cementing agency. Calcium chloride is normally used as the calcium source for the MICP process. The use of calcium chloride causes two problems. The first is chloride is corrosive to concrete, and the second is the cost of calcium chloride is relatively high. An improvement to this method is to use other alternative calcium sources. A method to produce soluble calcium using calcium rich calcareous sand and use it as a calcium source for the MICP process to improve the properties of soil has been proposed in this paper. A comparative study between the effect of MICP treatment using soluble calcium produced from calcareous sand and that using calcium chloride with the same concentration of calcium was carried out. The results from both series of tests showed that with increasing amounts of cementation solutions, the strength and stiffness of the treated calcareous sand increased and the permeability decreased. The scanning electron microscopy (SEM) and X-ray diffraction analyses revealed that the aragonite crystals with an acicular mineral morphology were formed when the soluble calcium was used, whereas the calcite crystals with a rhombohedral mineral morphology were formed when calcium chloride was used. This study also shows that it is feasible to treat calcareous sand using a MICP method with soluble calcium produced from calcareous sand.