Experiments And Applications Of Bio-geomaterials

The latest studies of biomineralization have shown that some micro-organisms, under suitable conditions, can induce significant precipitation of calcium carbonate in several days. This kind of microbial carbonate precipitation (MCP) has a composition similar to natural stone, at the same time this material can bond loose sand into a solid block. With a promising advantage in the strengthening of ancient masonry buildings as well as the ground improvement, this scientific discovery has been considered as the most important part of the newly developed interdisciplinary-Microbial Geotechnical Engineering, and has experienced an increased level of interest worldwide in recent years.In this study, Sporosarcina pasteurii was used for the microbial carbonate precipitation. We first produced MCP in test tubes and then characterized the microstructures of precipitated calcareous minerals with XRD, EDAX and SEM. The results confirmed the obvious MCP and two types of crystals: calcite and vaterite. The unique microstructures and mineral constitution could be responsible for the mechanical properties of MCP. A couple of factors affecting the reaction process were studied including the temperature, the nutrition solution concentration and the pH value of the system, etc. The generative capacity of MCP was also investigated in this study.Second, we tested whether this technique is applicable to the remediation of weathered rocks. The observations have shown that the MCP induced only in special locations of angular rock samples. But a layer of MCP was deposited covering rough surface of regular shape rock. This technique was also used for the crack-remediation of damaged bricks, and a tensile strength up to 0.5MPa was recoved.Last, we extended the application of this technique to the bio-cementation process of small sand cores. MCP cemented sand cores were subject to unaxial tensile test and the sand cores can reach a tensile strength of 0.2MPa. After treatment, observation of SEM showed that pore spaces were largely remained. A seriece of further experiments at larger scales were also taken place, aim to better understand and control the growth mechanisms of MCP in sand pores. The treated sand cores with larger scales had uniaxial compressive strengthes up to 1.38MPa. Calcium carbonate precipitated occupied 10%-17% of the pore volumes, and the samples after treatment still had high permeabilities between 6.383E-03~1.425E-02cm/s. Several factors including the biomass, the volume of the bacterial suspension, sand particle size distribution, the generation capacity of calcium carbonate, etc, should be considered in order to produce high quality Bio-GeoMaterials with desired strength, permeability and homogeneity.Through a series of experimental studies, this study verifies the possibility of applying the technique of MCP to the ground improvement and the restoration of ancient masonry buildings, thus provides a new method for these fileds.