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The geotechnical and microstructural properties of desilicated fly ash lime stabilised expansive soil


This study presents the use of marginal material as a stabiliser for expansive soil and therefore provides opportunity for high volume use of waste material for low cost, low volume road construction. Desilicated fly ash (DFA) was stabilised with lime up to 40 %. The effect of composite moisture content, lime content and curing temperature was studied. A 70:30 DFA:lime composite cured at 80 °C for 96 h had the highest unconfined compressive strength (UCS) of 8.57 MPa, a 19.5 % water absorption after a 24 h soak with a corresponding 23.5 % reduction in UCS. The green composite (70:30) was then used to stabilise expansive soil. Expansive soil stabilised with 30 % 70:30 DFA: lime composite was found to have a UCS of 4.1 MPa and resulted in a 50.1 % reduction in the liquid limit and a 15.1 meq/100 g reduction in cation exchange capacity of the soil. The formation of calcium silicate hydrate and tricalcium aluminate in the expansive soil was responsible for the strength gain in the stabilised soil. The stabilised soil met the minimum requirements for the American Concrete institute’s requirements for rigid pavement layers.

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The authors would like to thank the University Research Council of the University of Johannesburg for their financial support. The authors are also thankful to the National Research Foundation of South Africa for providing a bursary for the student.

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Correspondence to F. N. Okonta.

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Falayi, T., Okonta, F.N. & Ntuli, F. The geotechnical and microstructural properties of desilicated fly ash lime stabilised expansive soil. Mater Struct 49, 4881–4891 (2016).

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  • Desilcated fly ash
  • Durability
  • Saturation coefficient
  • Cation exchange capacity
  • Hydration