Stabilisation of soft marine clays susceptible to organic matter using metakaolin and slag based geopolymers

Cochin, located on the southern coastal belt of India, is characterised by extremely soft marine clays with organic matter posing significant challenges for construction activities. Traditional ground improvement techniques such as lime stabilisation are ineffective in strength improvement due to the unreacted organic fibres formed in the soil. This paper investigates the strength enhancement of clay soils through the application of two geopolymers synthesised from (i) ground granulated blast furnace slag, a high-calcium and (ii) metakaolin, a no-calcium aluminosilicate precursor. Unconfined compressive strength (UCS), pH, scanning electron microscopy, energy-dispersive spectroscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy were carried out on organic marine clay samples treated with slag-based geopolymers, metakaolin-based geopolymers and lime for long-term curing periods of 0, 7, 30, 90, 180, 365 and 730 days. The UCS of lime-treated organic clay initially increased to four times that of untreated clay, but slightly decreased after 90 days of curing period. The same organic clay, when treated with metakaolin/slag-based geopolymers, showed a continuous increase in strength, ultimately yielding UCS values on average of more than four times higher than lime-treated clays, indicating that both can serve as effective alternatives to conventional lime stabilisation in organic marine clays.