Influence of multiple treatment cycles on the strength and microstructure of biocemented sandy soil

Abstract

The strength of sandy soil can be improved via enzyme-induced calcium carbonate (CaCO3) precipitation (EICP). This method is a sustainable and environmentally friendly soil improvement technique that forms calcium carbonate between and around the soil particles. The formation of CaCO3 is achieved through the hydrolysis of urea that is catalyzed by free enzyme urease. This paper is divided into two parts. The first part explains the test-tube tests that were conducted to determine the amount and efficiency of CaCO3 precipitation at different concentrations of the cementation reagent (CCR). The second part describes the effects of multiple treatment cycles on the unconfined compressive strength (UCS) of EICP-treated soil. The soil samples were mixed with the EICP solution and compacted into PVC moulds. It was then followed by cycles of treatment with the EICP solution via surface percolation. The effectiveness of the bio-cementation was determined through a series of UCS tests. The results revealed that the UCS increased with higher CCR and more treatment cycles. The increase in UCS was also attributed to higher amounts of CaCO3 precipitated within the soil matrix. The highest UCS value of 1712 kPa was obtained at 1 M after the 3rd cycle of treatment with 8.21% CaCO3content. In conclusion, a higher number of treatment cycles demonstrated that increased deposition of CaCO3 precipitates increases the bonding effects and strength of the treated soil. Successful use of EICP in soil improvement will help in reducing sustainability concerns related to the production of conventional stabilizers such as cement.