Investigating Gas Entrapment Within Biocemented Composites

Abstract

Microbially-induced calcite precipitation (MICP), or biocementation, is a bio-mediated ground improvement method that can improve the engineering behavior of granular soils through the precipitation of calcium carbonate materials. While resulting bonds and particle coatings can provide large increases in soil initial shear stiffness, peak shear strength, and liquefaction resistance, alternative strategies such as microbial desaturation have shown the significant potential of increases in pore fluid compressibility to reduce excess pore pressure generation in contractive soils during undrained loading. In this study, a suite of experiments were performed to investigate the potential of novel biocementation treatment processes to enable entrapment of gasses within biocemented composites. Entrapped gas bubbles within biocemented materials may afford the ability to increase pore fluid compressibility and reduce excess pore pressure generation during undrained shearing following material damage and cemented bond fracture through the release of trapped gases. Batch experiments were employed to identify effective methods to both generate and entrap gasses within an organic polymer layer applied intermittently between biocementation treatments. During all experiments, aqueous chemical measurements were used to monitor cementation formation and gas entrapment processes with scanning electron imaging, material cross-sectioning, and energy dispersive spectroscopy employed to characterize achieved gas inclusions, material elemental composition, and resulting impacts on cementation morphology and fabric. Results suggest that gas voids can be successfully entrapped within biocementation through the application of organic polymers and microbial mixed acid fermentation (MAF) treatments, which can enable carbon dioxide production from both dissolution of existing biocementation and as a fermentation byproduct. Magnesium chloride treatment additions were also found to enable more effective coating of gas-containing polymer films during subsequent biocementation treatments when compared to control treatments not amended with magnesium. The novel biocemented composites developed through this research may enable significant improvements in engineering performances afforded by biocementation soil improvement and the environmental and financial efficacy of the technology.