Efficacy of soybean-derived crude extract in enzyme-induced carbonate precipitation as soil-improvement technique

Calcium carbonate precipitation using a urease enzyme, referred to herein as Enzyme-Induced Carbonate Precipitation (EICP) is a technique for soil improvement. In this technique, a mixed solution composed of reagents and the urease enzyme, which produces calcite, is utilized as the grouting material. Recently, alternative materials to the urease enzyme have been examined to resolve the cost issue of using the urease enzyme. In this study, several tests were conducted to compare commercial urease and soybean-derived crude urease. A comparison of their hydrolysis rates was done through urease activity tests. The microscopic structures and mineralogy of the precipitated materials, produced during various loading periods, were investigated through SEM and XRD analyses. Moreover, the reinforcing effect of the grouting solutions on the treated soil specimens was evaluated by measuring the unconfined compressive strength (UCS) of the treated samples. Interestingly, the precipitated CaCO₃ was vaterite and calcite when using soybean urease, while it was mostly calcite when using the urease enzyme. Higher UCS values were obtained with the soybean urease samples because the precipitated CaCO₃ seemed to be concentrated at the inter-grain contacts. It was concluded that soybean powder shows great efficacy as a replacement for commercially produced enzyme urease in soil-improvement techniques mediated by carbonate precipitation.