Unconfined Compressive Strength and Visualization of the Microstructure of Coarse Sand Subjected to Different Biocementation Levels

Abstract

Biocementation processes rely on microbial-induced calcite precipitation (MICP), which is a naturally occurring biochemical process. Biocement materials are a form of environmental cementitious agents used to improve the mechanical properties of granular soils by physically binding soil particles together. Efficient improvement of the macromechanical behavior of coarse sand treated by various amounts of biocement materials requires an in-depth understanding of its microstructure. This paper examined the effect of a number of bacterial suspension and cementation solution flushes on the macromechanical behavior of coarse sand. Also, X-ray computed tomography (XCT), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to investigate changes occurring at microlevels. The results show that compressive strength increased with an increase of biocement materials, and the maximum compressive strength achieved was around 14 MPa. The microscopic investigations were linked to the macromechanical changes, providing unique insight into the causation of the changes. Furthermore, several common soil properties (calcium carbonate content, dry density, void ratio, and porosity) were successfully identified using the XCT technique.