Abstract
Calcium carbonate precipitation and crystallization induced by urease enzyme to solidify soil is known as biocement technology. The uses of waste and cheap materials can make this technology more cost-effective and practical for applications. In this study, calcium ions were obtained by dissolving waste concretes in acidic liquid. Sand columns were treated by enzyme-induced carbonate precipitation (EICP) with either concrete-extracted calcium or reagent calcium for comparison. Compressive strengths, calcium carbonate contents, and microscopic analysis on the treated sand were carried out. It was found that the compressive strength of the former could reach 833 kPa in the dry state and 204 kPa in the wet state after 5 times of EICP treatment, both of which were higher than that of the latter. The calcium carbonate contents could reach 2–3% after 3–5 times of treatment. Based on the scanning electron microscope (SEM) and X-ray diffractometer (XRD) analyses, the crystal type of calcium carbonate produced in sand was calcite. The comparative results showed that the treatment effect using concrete-extracted calcium was similar or better than that using reagent calcium.
Highlights
Calcium carbonate precipitation induced by the microbial ureolytic process can be utilized as an engineering tool for soil solidification [1,2,3]
Between the sand specimens treated with concrete-extracted calcium and reagent calcium, there was no significant difference in dry strengths after three and four treatments, and the dry strength of the former was greater than that of the latter at 5 times of treatments
Sand specimens treated with concrete-extracted calcium and reagent calcium had no significant difference in strength at both the dry and wet states
Summary
Calcium carbonate precipitation induced by the microbial ureolytic process can be utilized as an engineering tool for soil solidification [1,2,3]. The microbial ureolytic process can be catalyzed by either ureolytic bacteria or urease enzyme, which is named microbial-induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) [4, 5]. MICP or EICP for soil cementation, or biocement technology, usually requires large amounts of calcium chloride as the calcium source. Some researchers have studied the feasibility of replacing calcium chloride with soluble calcium sources from domestic waste [9, 10]. Choi et al [9] mixed eggshells and vinegar to obtain soluble calcium sources for sand treatment. The results showed that using eggshells as the calcium source for MICP treatment had roughly the same effects compared with that using reagent calcium chloride
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