Performance of biocemented sand under various environmental conditions
Donovan Mujah1; Mohamed Shahin1; Liang Cheng1
1 Curtin University
Resumo
Microbially induced calcite precipitation (MICP) is a naturally driven biological technique that employs the use of ureolytic bacteria to hydrolyse urea, producing carbonate ions. In the presence of a calcium rich medium, carbonate ions react with calcium ions to form a solid compound called calcium carbonate or calcite (CaCO3). The precipitated CaCO3 would act as a cementing agent that binds the soil grains together by means of effective bridging at the soil pore throats, leading to increased strength and stiffness of biocemented soil. In this study, the performance of biocemented uniform silica sand (0.425 mm in diameter) under extreme environmental conditions were investigated, including: (1) low, ambient and high surficial temperatures; (2) different soil pH; and (3) two freeze-thaw (FT) cycles conditions (4 FT and 10 FT). The study was carried out through a series of laboratory tests including the determination of the CaCO3 content, the pre and post hydraulic conductivity and the unconfined compressive strength (UCS). The crushed biocemented samples were observed at the microscale level using the scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), to analyse the microstructure and chemical characterisation of the precipitated CaCO3. The UCS results indicated that soil biocementation is more effective at the ambient temperature and neutral soil pH. Moreover, the results also demonstrated that the biocemented sand was able to withstand up to 10 FT cycles. Although all biocemented samples recorded reduction in their hydraulic conductivity values, regardless of the environmental parameters tested, the ability to retain sufficient permeability while ensuring fairly adequate strength compared to traditional chemical treatment by Portland cement was a clear advantage of MICP treated soil. The SEM images of the biocemented samples confirmed the formation of effective bridges that connect the voids of soil grains, leading to improved soil strength and stiffness. The EDS analysis verifie
Palavras-chave: Biocementation; Microbially induced calcite precipitation (MICP); Soil stabilisation; Ground improvement