Single MICP treatment method for soil improvement using pH adjustment and milk

Microbially induced calcite precipitation (MICP)-based biocementation methods for soil improvement have drawn a substantial amount of attention in recent years. However, this method still suffers from several shortcomings. One of them is the need for multiple treatments. This paper presents a new method to enable a shear strength gain of more than 1 MPa to be achieved from a single MICP treatment. The key challenge is to use a cementation solution having a high calcium ion concentration. It is known that an excessively high calcium ion concentration will cause a retarding effect to impede the MICP process. In this study, a buffer solution and milk were used to enable a high calcium conversion efficiency of 95.5% for an all-in treatment solution with 2 M calcium ion concentration. By controlling the pH of the solution and using full cream milk, we could obtain an unconfined compressive strength of 1049 kPa from a single MICP treatment in 1 day. It was also discovered that the type of milk used could affect the strength of the soil treated and the use of full cream milk resulted in a higher strength than that of skim milk.