Stabilisation of estuarine sediments with an alkali-activated cement for deep soil mixing applications

In this work, an alternative alkali-activated cement (AAC) made of ladle slag precursor mixed with sodium hydroxide and sodium silicate has been developed to enhance the bearing capacity of estuarine soils in coastal conditions via deep soil mixing (DSM). The AAC was optimized to use a low reactivity precursor (ladle slag) and to deal with a contaminated high-water content natural sediment cured under water. The material performance was analysed by comparison to a mixture made with Portland cement and cured in the same conditions. Flexural and unconfined compressive strength tests as well as seismic waves measurements after 3-, 7-, 14- and 28-d curing were performed to obtain a relationship between elastic stiffness and strength with curing time for both mixtures. Remarkably, the AAC mix demonstrated superior strength results, exhibiting almost double flexural and compressive strengths after 28 d compared to the Portland cement mix. The AAC mix also showed a higher rate of stiffness increase than the Portland cement mix, which has a higher initial stiffness at young ages but lower stiffness evolution. Leachate analysis confirmed that the proposed AAC could effectively immobilise any contaminants from soil or precursors. The effect of curing under stress was analysed in triaxial compression tests and found to be insignificant, indicating that laboratory data obtained without stress curing can represent the material's behaviour in a DSM column, which will cure under the weight of the column.CNPq (Brazilian council for scientific and technological development) through 201465/2015-9 scholarship of the “Science without borders” program