Stabilization of highly expansive soils containing sulfate using metakaolin and fly ash based geopolymer modified with lime and gypsum

High sulfate expansive soils present special challenges during stabilization. Traditional stabilizers such as lime and cement which are rich in calcium are ineffective in controlling shrink/swell behavior of these soils due to formation of the expansive mineral, ettringite. In this study, two geopolymers synthesized from aluminosilicate sources, fly ash and metakaolin, were investigated to determine their effectiveness in stabilizing shrink-swell behavior of high sulfate expansive soil. Geopolymers were modified with lime and gypsum to improve their efficacy as stabilization agents for sulfate bearing soil. Modifier contents were optimized to achieve maximum reduction in swell potential and at the same time prevent ettringite formation. Microstructural analyses were performed on lime and gypsum added geopolymer to determine the mechanism of modification. Swell tests were conducted on high sulfate soil treated with modified geopolymer at different concentrations and optimum concentration of modified geopolymer required to achieve minimum swell was established.