The purpose of this study was to assess the performance of high water content clayey sediments at different liquid limits as the clays are treated with cement-based solidifying materials. Three clay samples are obtained from different locations in the Kumamoto Reservoir. Two types of cement-based solidifying agents, namely, ordinary Portland cement and a cement–fly ash binder, were used. Using the initial water content of clay and the mixing amount of the solidifying agent as experimental variables, a cone penetration test was performed on the solidifying agent-stabilized clays to obtain the cone index (q_c). The results showed that when the water content to cementitious content ratio (w/A_W) was used as a parameter for evaluating the improvement of solidifying agent-stabilized clay, different forms of improvements were observed when different water and solidifying agent contents were used. This implied that the parameter w/A_W was not suitable for evaluating the improvement of such clay. A new parameter, K, representing the content of solidifying agent, was introduced to account for the water content. For all sampled clays, the correlation coefficients for the K–ln q_c relationship exceeded 0.9. Considering the effect of the liquid limit of the samples, the modified content of the solidifying agent (K_L) was introduced to evaluate the cone index of the stabilized soils. It was discovered that the proposed equation unified the assessment of the improvement of the three samples of Kumamoto clayey sediments owing to the new parameter, K_L.

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.