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This paper presents a novel laboratory experiment that can be incorporated into introductory soil mechanics courses to introduce students to the field of biogeotechnical engineering and the use of biostimulated microbially induced calcite precipitation (MICP). Applying MICP to granular soils results in an increase in peak strength and shear stiffness of the soil as a result of the precipitation of calcium carbonate on soil particle surfaces and at soil particle contacts. The authors developed protocols to treat small volumes of soil and to test the effectiveness of the treatment using a simple strength test based on ASTM D3967-16. In fall 2020, the experiment was piloted as a four-week, course-based research experience that can be conducted by students remotely or in a traditional laboratory environment. This paper provides an introduction to MICP and describes the protocols for conducting the experiment. The paper also suggests approaches for how the experiment can be incorporated into a traditional introductory soil mechanics course.
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Evaluation of Geopolymer for Stabilization of Sulfate-Rich Expansive Soils for Supporting Pavement Infrastructure
Stabilization of sulfate-rich expansive subgrade soils is a persistent cause of concern for transportation infrastructure engineers and practitioners. The application of traditional calcium-based stabilizers is generally not recommended for treating such soils because of the formation of deleterious reaction products such as ettringite. Sulfate-induced heaving causes severe structural damage to pavements and accounts for enormous expenditure from routine maintenance and rehabilitation activities. A research study was undertaken to evaluate the feasibility of using a metakaolin-based geopolymer (GP) for the treatment of sulfate-rich expansive soil. Laboratory studies were conducted on natural soil and artificially sulfate-rich soils, when treated with either lime or GP, to evaluate and compare the improvements in the engineering properties, including unconfined compressive strength, swelling and shrinkage, and resilient moduli characteristics over different curing periods. Microstructural studies, such as field emission scanning electron microscopy and X-ray diffraction, were performed on treated soils to detect the formation of reaction products. The engineering studies indicate that GP treatment enhanced strength and resilient moduli while suppressing ettringite formation and the associated swell–shrink potential of the treated soils. The microstructural studies showed that GP gels contribute to the improvement of these engineering properties through the formation of a uniform geopolymer matrix. In addition, the absence of a calcium source suppressed the formation of ettringite in the GP-treated soils. Overall, the findings indicate that GPs could be used as a potential alternative to existing traditional stabilizers for treating sulfate-rich expansive soils.
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- Award ID(s):
- 2017796
- PAR ID:
- 10380414
- Date Published:
- Journal Name:
- Transportation Research Record: Journal of the Transportation Research Board
- Volume:
- 2676
- Issue:
- 9
- ISSN:
- 0361-1981
- Page Range / eLocation ID:
- 230 to 245
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1177/03611981221086650
