A laboratory study of the effects of bio-stabilization on geomaterials
This study was designed to test the effects of bio-stabilization on geomaterials as an alternative to chemical and mechanical stabilization. Microbially induced precipitation was used as a method of bio-stabilization. An indigenous microorganism, Bacillus pasteurii, was used to prompt calcite and other precipitates that stabilized geomaterials. A standard procedure for bacteria cultivation and bio-treatment soil stabilization and aggregate coating was developed. Two types of liquid incubation medium, one containing NH4Cl and one containing (NH4)2SO4, were tested. After conducting unconfined compression tests, it was discovered that both medium work well for bacteria incubation and treated samples have similar strength performance. In addition, double bio-treated samples were stronger than single treated samples, and oven-dried bio-treated samples were stronger than air-dried treated samples.
In aggregates, lower porosity helps to resist the negative effects of freezing and thawing. Mercury intrusion porosimetry confirmed that bio-treatment decreased the porosity of aggregates. At five to six bio-treatment cycles the lowest porosity values were achieved. More than six cycles of bio-treatment showed an increase in the porosity. Scanning electron microscopy and X-ray diffraction, were conducted and confirmed that bio-treatment produces precipitate coatings on the surfaces of aggregate. Dynamic modulus tests of concrete beams with bio-treated aggregates showed that treated aggregate improved the durability of the concrete. Freeze-thaw soundness tests on the treated aggregate confirmed these results. This is believed to be the first study of its kind.