The solidification of dredged marine sediments with high water content is important for maintenance dredging and reclamations. To reduce the carbon emission of solidification, low-carbon recycled wastes such as incinerated sewage sludge ash (ISSA) and ground granulated blastfurnace slag (GGBS) have been recently adopted as binding materials to replace conventional Portland cement. For soil slurry with ultra-high water content, using the consolidationsolidification combined method is an effective way to reduce the volume and improve the final mechanical properties. However, it is unclear how the consolidation interacts with solidification using the binding materials. In this study, a series of laboratory tests were conducted on dredged Hong Kong marine deposit slurry mixed with ISSA and GGBS with alkali activation by lime. The elemental consolidation tests controlled with different constant rates of strain and multistage loadings demonstrate that the rate of consolidation has significant effects on volume reduction and yielding stress development during consolidation-solidification treatment. Consolidationsolidification achieves higher volume reduction and yielding stress than pure solidification. As the rate of consolidation decreases, there is a smaller volume reduction at the same effective stress and less yielding stress enhancement at the same curing time. A scanning electron microscope with energy dispersive spectrometer was used to investigate hydration products and soil fabric after treatment. The slower rate of consolidation causes the looser structure and finer needleshaped products with the same curing period, which can explain the mechanical properties observed from the element tests.

Deep cement mixing (DCM) is a popular in situ soil stabilization method, while the investigation on long-term coupled consolidation and contaminant leaching behavior of cement-stabilized contaminated soil is limited. In this study, axisymmetric physical model tests were conducted to investigate the coupled behaviors of a composite ground, which consisted of a central column made of cement-stabilized arsenic-contaminated marine deposits and surrounding untreated marine deposits. The test results revealed the settlement development of composite ground and the mechanism of load transfer between the DCM column and surrounding soils with increasing loading. The presence of arsenic decreased the strength and stiffness of the DCM column through the reaction between arsenic and hydration and pozzolanic reaction products. With the increase of the water/cement ratio in the DCM column, the concentration level of arsenic in the draining-out water of the composite ground increased significantly, while that in the surrounding soil showed no obvious change, indicating that arsenic mainly migrated directly through the DCM column. A theoretical axisymmetric consolidation model coupling solute transport for composite ground was established and subsequently applied to analyze the test data. The numerical model accurately depicted the pore water pressure, settlement, and spatiotemporal distribution of arsenic concentration in the physical model.

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.