Effect of seawater on solidification/stabilisation treatment of marine soft soil slurry by lime-activated ISSA and GGBS

Abstract

It is proposed to use dredged marine sediments as fill material in marine reclamation engineering by stabilisation/solidification (S/S) technology with sustainable binding materials, which can help the soft soil gain strength to solve the engineering geological problem of its insufficient bearing capacity. In this work, lime and two types of industrial wastes, i.e., incinerated sewage sludge ash (ISSA) and ground granulated blast-furnace slag (GGBS), were selected as the binding materials. Hong Kong marine deposits (HKMD) slurry with a high initial water content of 110% was mixed with 30% binders (30% lime and 70% (ISSA+GGBS) with ISSA: GGBS = 3). The seawater (SW) with salinity of 3.6% was employed as mixing solution in S/S treatment of HKMD. To detect the effect of each main composition in SW on the performance of S/S HKMD, the pure solutions of NaCl, MgCl2 and Na2SO4 were adopted in this study. The results show that the use of SW in the lime-activated ISSA and GGBS treated dredged HKMD slurry is effective in improving its strength. The X-ray diffraction, thermo-gravimetric analysis and scanning electron microscopy observations present the formation of calcium/magnesium silicate hydrate (C/M-S-H), Friedel's salt and ettringite, which fill into the pores and interlock the particles in the mixture increasing the strength of the treated HKMD. The chemical compositions of SW have significant and different impacts on the performance of treated HKMD samples. Na+ can help the samples gain higher strength and result in the cracking development in the S/S samples. Mg2+ will lead to the formation of M-S-H, which reduces the porosity of treated HKMD samples. However, the contribution of M-S-H to the soil strength is less than that of C-S-H. Cl− in the mixture would slow down the reaction speed and show slight impacts on the modulus. SO42− accelerates the reactions in the treated samples and has a more significant effect on nano-size porosity of bulk sample. Consequently, the seawater has positive effect on the S/S performance of HKMD slurry, suggesting potential application in the practical projects.