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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Self-healing Capacity of Strain-Hardening Fiber Reinforced Geopolymer Composites
This study reports on the self-healing capability of a strain-hardening fiber reinforced geopolymer composite, named Engineered Geopolymer Composite (EGC). EGC specimens were first uniaxially loaded to a tensile strain of 1%. The cracked specimens were then subjected to three different conditioning regimes: air curing, water curing, and no curing (i.e. reloading right after the preloading). Stiffness reduction was measured for each series by comparing the initial stiffness of intact specimens and the residual stiffness of the cracked specimens. In the water-cured specimens, white precipitates were observed in microcracks formed by preloading. Experimental results of the series showed significant stiffness recovery for low stress levels in the range of 0.5 – 1.0 MPa. Self-healing products observed by using a scanning electron microscope were mostly angular, stone-like substance. An analysis of energy dispersive spectroscopy showed that the healing products were relatively rich in silicon (Si) and aluminium (Al) and had lower concentration of calcium (Ca), compared to the geopolymer matrix phase. This implies that main product of EGC self-healing is unlikely to be either calcite (CaCO3) or salt deposits such as Na2CO3, but rather a formation of some aluminosilicate compounds. This study provides a baseline for further investigations into the development of geopolymer composites with robust self-healing.
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- Award ID(s):
- 1634694
- NSF-PAR ID:
- 10148595
- Date Published:
- Journal Name:
- fib Symposium on Concrete Structures for Resilient Societies
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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