Strength reduction mechanism of cement-treated soil under seawater environment

Improving soft grounds with cement or lime is commonly used to increase their strength and deformation characteristics. However, the properties of cement/lime-treated soil deteriorate in seawater because magnesium salts accelerate calcium leaching. In this study, changes in the unconfined compressive strength of cement-treated soil samples with various water contents, amounts of added cement, and curing times were investigated after immersion in a highly concentrated Mg solution. Subsequently, a thermogravimetric-differential thermal analysis and scanning electron microscopy were used to determine the strength reduction mechanism based on the changes in the hydrate composition as the cement-treated soil deteriorated. The results indicate that the cement-treated soil lost more than 80% of its strength after immersion in the Mg solution. The initial conditions strongly influenced the strength of the deteriorated soil, and higher strength was observed in the samples with larger amounts of added cement and longer curing times. Furthermore, calcium silicate hydrate (C-S-H) and ettringite were not present in the deteriorated soil, implying the presence of magnesium silicate hydrate (M-S-H). Therefore, it was postulated that the loss in strength of the cement-treated soil in a seawater environment was caused by the transformation of C-S-H to M-S-H.