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Application of Microbial Induced Calcite Precipitation to Stabilize Florida High-Organic Matter Soils for Roadway Construction
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Application of Microbial Induced Calcite Precipitation to Stabilize Florida High-Organic Matter Soils for Roadway Construction
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    Final Report, 01/2016 – 03/2019
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    Microbially induced calcite precipitation (MICP) was used to treat Ottawa 50-70 sand and organic soil (from Polk County, FL, with 50% organic content) in the lab via injection at the bottom of specimens. Results showed that the technique was effective in sands, although calcification was variable and not uniform over the height of each specimen, which resulted in variability in the laboratory strength tests. In an effort to create specimens with uniform calcification, a pre-mixing treatment methodology was developed. Results from pre-mixing showed that more-uniform specimens were created. Both injection and pre-mixing MICP techniques were used to treat the organic soil. Results showed that very little calcite was created using either treatment technique. However, the pre-mixing technique was slightly more effective for specimens with lower organic content (10%). Exopolysaccharide (EPS) formation and the role it plays in MICP was investigated. EPS was observed in samples of MICP-treated Ottawa sand and appears to be a necessary component in the process for successful calcification. The inability to calcify in the organic soil may be due to the lack of EPS, which suggests its formation is inhibited by organic matter. A preliminary study was conducted to assess the feasibility of using bio-stimulation (stimulating native soil microbes) to induce calcite formation in Florida soils. While results showed that the treatment was ineffective, this was expected based upon results from bio-augmented treatments. In an attempt to induce calcification in the organic soil, sodium dodecyl sulfate (SDS) was added to the MICP recipe. While preliminary results were very promising, further investigation showed that specimens treated with SDS-MICP were dissolvable. In addition, results showed an unintended formation of a calcium dodecyl sulfate (CDS) complex that when stoichiometrically balanced, yielded specimens that were very strong and insoluble. This new, unstudied, non-traditional soil treatment technique has been dubbed surfactant-induced soil stabilization (SISS). The SISS method was further investigated as a viable means for treating Florida soils, although a thorough investigation of this soil treatment technique was outside the scope of this project. Preliminary results of SISS-treated specimens are very promising and warrant further investigation.
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