Abstract
Expansive soils generally recognized as swell-shrink soils have been a problem for civil infrastructure for a long time. Engineers are in search of sustainable stabilization alternatives to counter these problematic soils. Microbial-induced calcium carbonate precipitation (MICP) is a promising biocementation process that can improve the properties of expansive soil through calcium carbonate precipitation. Past research has shown promise for the use of MICP in mitigating swelling distress from expansive soils. In this research, MICP via biostimulation was attempted by mixing enrichment and cementation solutions with soils in an effort to develop a new alternative to shallow chemical stabilization. Three soils with varying clay contents (30%, 40%, and 70%) and plasticity characteristics were selected, and soils were treated by mixing with enrichment solutions followed by cementation solutions. Five different mellowing periods, three different curing periods, and two types of cementation solutions were studied to optimize the method. Treatment effectiveness was evaluated using unconfined compression tests, calcium carbonate tests, and free swell index tests. Results showed that an increase in the mellowing period beyond two days was not beneficial for any of the three soils tested in this research. It was determined that the best improvement was observed at two days of mellowing and seven days of curing.
Highlights
Expansive clays are often associated with low bearing capacity, high compressibility, along with swelling and shrinkage behavior
Biostimulation is a type of Microbial-induced calcium carbonate precipitation (MICP) process where indigenous microbes are stimulated to precipitate calcium carbonate
Test data was examinedafter to study the effect parameters the volume of soil The submergence in of water mellowing curing periods, type of cementation solution, and the type oftest, soil on the and theand volume of soil after submergence in kerosene
Summary
Expansive clays are often associated with low bearing capacity, high compressibility, along with swelling and shrinkage behavior. Biostimulation is a type of MICP process where indigenous microbes are stimulated to precipitate calcium carbonate. Chittoori et al [9] studied biostimulation in clayey soils by injecting substrate solutions under high pressures They noted that calcium carbonate precipitation was possible by injecting treatment solutions at high pressures. A new MICP application approach is evaluated by mixing substrate solutions with soil, similar to mixing lime or cement in case of chemical stabilization. In this novel approach, soil samples were first mixed with enrichment solutions to stimulate the bacteria, followed by cementation solutions to precipitate calcium carbonate. Optimized the concentration of calcium to be used in biomineralization using stimulated indigenous bacteria
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