Implementation of eggshell extracted calcium acetate in biocementation via soybean urease

Abstract

Biocementaion, a promising soil improvement technique, mostly utilizes calcium chloride (CaCl2) as its calcium source. However, using CaCl2 poses a critical environmental problem of producing ammonium chloride as a by-product. Alternatively, when calcium acetate (Ca(CH3COO)2) is used as the calcium source, the production of ammonium chloride during biocementation can be reduced. Ca(CH3COO)2 can be easily derived from waste eggshells. Nevertheless, such research has been conducted only with Microbial Induced Carbonate Precipitation (MICP) to date. This paper aims to study the implementation of eggshell Ca(CH3COO)2 in the more effective biocementation approach: Enzyme Induced Carbonate Precipitation (EICP) via soybean urease. For this study, EICP solutions of varying molar ratios and concentrations were studied for their precipitation efficiency and reinforcement effect on poorly graded sandy soil. The findings showed that the EICP solution composition of 1:1 molar ratio between Ca(CH3COO)2 and urea, added with 50 g/L soybean solution reached the maximum precipitation efficiency. It also produced the highest 7-day UCS of 371 kPa at a calcium carbonate content of 0.40%. Furthermore, the eggshell-soybean EICP produced 8.5% higher UCS than CaCl2-soybean EICP despite having similar calcium carbonate content.