This study aims to evaluate the possibility of reusing treated marine clayey soils by stabilization/solidification (S/S) technology as geomaterial in reclamation projects from the aspects of engineering strength, chemical modification and environmental risk assessment. The lime-activated incinerated sewage sludge ash (ISSA) together with ground granulated blast furnace slag (GGBS) was employed as the binder. The multi-controlling factors including water content, curing time, salinity, and chemical compositions of mixing solution were taken into account to identify the S/S treated Hong Kong marine deposit (HKMD) slurry based on the strength tests, pH measurement, thermo-gravimetric (TG) analysis, X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS) and toxicity characteristic leaching procedure (TCLP) tests, etc. The results show that the S/S treatment using lime-activated ISSA-GGBS can effectively enhance the strength of marine soil at the initial water content of 110% and 200%. The water content and curing time have a significant impact on the S/S treated HKMD. The pH of treated soils is higher than 11.1, which proves an alkaline environment for the reactions in the treated soil. A special case is the treated HKMD at 200% water content hydrated by MgCl2 solution, which has a low pH of 10.23 and maintains a slurry state. Based on the TCLP results, the leaching concentration of heavy metals from S/S treated HKMD is environmentally safe and meets Hong Kong standard for reusing treated soil with a low level of <0.2 mg/L. The content of main products such as calcium/magnesium silicate hydrate, ettringite or Friedel's salt depends on the chemical additions (e.g. distilled water, seawater, NaCl and Na2SO4). The products in the specimens mixed with MgCl2 solutions are mainly composed of Mg(OH)(2), M-S-H and MgCO3, which is distinct with the neoformations in the other cases. Therefore, this study proves that the S/S treated soil slurry could be reused as geomaterials in reclamation projects, and the S/S process is greatly affected by water content, curing time and solution compositions, etc. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

This study sheds light on the engineering and environmental performance of lime-activated incinerated sewage sludge ash (ISSA) and ground granulated blast furnace slag (GGBS) treated Hong Kong marine deposits (HKMD) slurry by stabilisation/solidification (S/S) technology, which is proposed using as fill materials in reclamation projects. The S/S performance of the treated HKMD with distilled water and seawater under different salinities was investigated. The results show that seawater could help S/S treated HKMD gain strength by using activated industrial wastes (ISSA and GGBS). The hydration and pozzolanic reactions between ISSA, GGBS, CaO and clayey compositions in HKMD make contributions to the strength development, porosity decrease and heavy metals stabilisation, which is supported by the characterization analysis including thermo-gravimetric (TG) analysis, mercury intrusion porosimetry (MIP) tests, nitrogen adsorption/desorption isotherms (NAI), scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS) and the leaching test of toxicity characteristic leaching procedure (TCLP). Seawater of 1.8% salinity (18 g/kg) is better than the distilled water and seawater of 3.6% salinity as a substrate solution in the S/S treated HKMD, because of the highest unconfined compressive strength and lowest porosity in the treated samples. The highest pH may account for its highest strength under the 1.8% salinity conditions. The S/S process could effectively stabilize the contaminants regardless of the curing time and the salinity of the mixing solution, and the leachates from the stabilized HKMD are environmentally safe and meet the requirement of standard in Hong Kong on the recycling treated soil. Therefore, recycling wastes-ISSA and GGBS with lime can be used as an appealing binder to stabilize/solidify marine deposits as environmental-friendly reusable materials in reclamation projects.