The effective and sustainable treatment of high-water-content waste dredged clay (WDC) remains a significant challenge in water conservancy engineering. In this study, we focused on the treatment of WDC produced by Kumamoto Ohkirihata Reservoir. The study examined the effect of two types of cement-based solidifiers, namely, ordinary Portland cement (OPC) and cement–fly ash agent (DF), on three clay samples collected from different locations. The cone index test was used to assess the samples’ properties. The dosage of cement required for effective improvement with DF was significantly reduced (by about 47–55%), compared to OPC. Moreover, the dewatering efficiency of WDC improved by the simple dewatering method of vertically placing environmental protection materials. Within seven days, the average water content of the WDC decreased to below the liquid limit compared with natural air drying. Finally, the dosage of DF required to stabilize the WDC under effective improvement conditions was reduced by 37–58%, which is higher than the dosage of OPC reduction (22–50%). The reduction in water content reduced the pore space of the soil particles, benefiting the internal bonding of DF-stabilized clay. Dewatering methods facilitate the use of DF solidifiers, facilitating sustainable and environmentally friendly improvement in WDC.

This review examines recent advances in hydrated lime-activated systems using hydrated lime (HL) as the sole alkaline activator, with particular emphasis on the effects of reactive precursors and auxiliary materials on mechanical properties and carbonation behavior. Compared with conventional strong alkali activators, HL provides a milder alkaline environment and an additional Ca source, promoting precursor reactions and the formation of C–S–H, C–(A)–S–H, and other calcium-containing hydration products. Precursor characteristics, multicomponent mixture design, water-to-binder ratio, and curing conditions strongly influence reaction kinetics, strength development, hydration products, and microstructure. Carbonation is a key process that distinguishes hydrated lime-activated systems from conventional strong alkali-activated systems and plays an important role in their microstructural and mechanical development. It has a dual effect on material performance, as it can contribute to matrix densification but may also lead to the degradation of calcium-containing binding phases as carbonation progresses. Therefore, material composition and curing conditions should be considered together to balance mechanical performance and carbonation behavior. From a sustainability perspective, hydrated lime-activated systems show promise in by-product utilization, reduced use of conventional strong alkalis, substitution of OPC, and CO₂ uptake through mineral carbonation. Further systematic studies are needed to evaluate these potential sustainability benefits.

High-water-content dredged clay is a water-rich sediment that requires sustainable, resource-oriented treatment, but conventional ordinary Portland cement (OPC) stabilization is hindered by excessive water-to-binder ratios, suppressed hydration, and high carbon emissions. This study investigated corn straw biochar (CSB) as a partial OPC substitute for the low-carbon stabilization of kaolin-based simulated dredged clay. CSB prepared at 200–1000 °C under different holding times was characterized by water absorption, thermogravimetry, and SEM. Clay specimens with an initial water content of 80% (1.5 w_L) were prepared using 5–12% total binder, CSB:OPC ratios of 5:5–8:2, and curing ages of 7 and 28 d, and were evaluated by UCS, pH, SEM/ESEM, EDS, and life-cycle-based mechanical–environmental assessment. CSB developed honeycomb-like interconnected pores and a lamellar carbon skeleton, reaching 1476.10% water absorption at 700 °C for 30 min. The optimum CSB–OPC specimen reached approximately 136–137 kPa at 28 d, exceeding the OPC-only control of about 102 kPa. Strength improvement was associated with alkalinity maintenance, Ca–Si-rich hydration products, pore filling, and CSB–clay interfacial adsorption, embedding, and encapsulation. Properly carbonized CSB shows potential as an internal-curing, low-carbon co-binder for simulated dredged clay, but its field applicability requires further validation.