This study investigates the evolution of the dynamic characteristics of a solidified dredge sludge, including the resilient modulus (MR), accumulative plastic strain (epsilon p) and damping ratio (lambda) during long-term traffic loadings considering influences of environmental actions (dry-wet, DW, and freeze-thaw, FT cycles), stress states (confining stress sigma cand deviator stress sigma d) and loading frequency (f). The experimental results indicate that the dynamic characteristics continuously change with increasing loading cycles and the influences of environmental actions, external stress state, and loading frequency are coupled. The resistance of the solidified sludge against traffic loading decreases after both DW and FT cycles, which is manifested by the decrease in the MR and the increase in the lambda and epsilon p. DW cycles induce greater reductions in the dynamic characteristics than the FT cycles. The increasing sigma c improves the resistance of the soil against cyclic loadings, resulting in higher MR and lower epsilon p and lambda. Besides, their rates of change with loading cycles (i.e., delta MR, delta epsilon p and delta lambda) reduce. The MR, epsilon p, lambda, and delta ap increase while the delta MR and delta lambda decrease with the sigma d, indicating that the increase in the cyclic loading level contributes to the accumulation of plastic strain and energy assumption while the resultant densification effect leads to the increase in the MR and decrease in the delta MR and delta lambda. The soil dissipates less energy when loaded under higher f, resulting in higher MR and lower epsilon p and lambda. Results reported in this paper are helpful for better understanding the dynamic responses of solidified sludge under complex loading and environmental conditions.

This study explores the application of calcium carbide residue, desulfurization gypsum, and ground granulated blast slag as curing agents to solidify sludge. Through indoor experiments simulating dry-wet cycles and sulfate erosion, using unconfined compressive strength (UCS), X-ray diffraction, and scanning electron microscope as testing methods, the durability of solidified sludge against dry-wet cycles and sulfate erosion was studied. The objective is to provide technical support for the application of solidified sludge in engineering projects and promote the resource utilization of industrial solid waste. The results indicate that solidified sludge exhibits excellent durability against dry-wet cycles and sulfate erosion, with improved durability as the dosage of curing agent increases. In terms of dry-wet cycles, UCS initially increases but experiences a certain degree of decline as the number of dry-wet cycles increases, with the strength change rate exceeding - 35%, and failure strain gradually increases. As for sulfate erosion, UCS initially decreases following 1 day of erosion and subsequently shows a gradual improvement as the erosion time progresses. Higher sulfate concentrations lead to higher UCS, with strengths reaching up to 2.102 MPa, and failure strain gradually decreases. Microscopic tests revealed that, although dry-wet cycles initially weaken the structure and network of solidified sludge, increasing dry-wet cycles numbers leads to enhanced hydration reactions, resulting in higher content of hydration products and a denser microstructure. Experimental results indicate that using calcium carbide residue, desulfurization gypsum, and ground granulated blast slag as curing agents for sludge results in excellent resistance against dry-wet cycles and sulfate erosion.

Massive dredged sludge is being landfilled without effective use due to its high-water content and poor engineering properties, which not only leads to soil resources waste, but also occupies a large amounts of land sources. In this study, ternary stabilizer, including waste phosphogypsum (PG), ground granulated blast-furnace slag (GGBS), and lime (LM) with a mixing proportion of PG: GGBS: LM = 35:60:5, was adopted to improve the mechanical and environmental behaviors of sludge for subgrade filling purpose. The initial water content of sludge was controlled using two different dehydration methods for comparison. A series of laboratory tests, including unconfined compressive strength (UCS), organic matter content, and pH value were tested to understand its physical-mechanical properties. Thereafter, field application model equipped with a mini weather monitoring station was constructed to monitor the influence of solidified matrix on the surrounding water and soil environment. Time -dependent parameters such as plant growth, temperature, humidity, total nitrogen, phosphorus/potassium content, electrical conductivity, and pH value were monitored. Results indicate that the incorporation of PG-GGBS-LM ternary stabilizer significantly improves the mechanical and environmental properties of dredged sludge. The optimal dosage of the ternary stabilizer is 36%, which can result in a UCS value of the 2.0 MPa (slightly higher than ordinary Portland cement) after 28 days of curing. Field application reveals that plants could grow normally in solidified sludge. The environmental related parameters (i.e., total nitrogen, phosphorus/potassium content, electrical conductivity, and pH value) were similar with those in conventional planting soil, suggesting the advantage of the proposed PG-GGBS-LM ternary stabilizer in mechanical, economic and environmental aspects.

This paper utilizes industrial wastes, including slag powder, desulfurized gypsum, fly ash, and construction waste, to solidify municipal sludge and develop a new type of landfill cover material. To investigate the durability of solidified sludge under wet-dry cycles, this study systematically analyzes its mechanical properties-such as volume shrinkage rate, unconfined compressive strength, and permeability coefficient-along with microstructural characteristics like pore structure, micro-morphology, and hydration products. In addition, the impermeability of the solidified sludge cover under varying rainfall conditions was assessed using rainfall simulation tests. After 20 wet-dry cycles, the solidified sludge samples exhibited volume shrinkage between 0.56% and 0.85%, unconfined compressive strength from 1.31 to 4.55 MPa, and permeability coefficients ranging from 9.51 x 10- 8 to 5.68 x 10- 7 cm/s. Portions of the gelatinous hydration products in the solidified sludge experienced discrete damage, leading to an increase in microporous volume. However, the overall structural integrity of the solidified sludge was maintained. The 3-layer landfill cover system was constructed using engineering soil, coarse construction waste aggregate, and solidified sludge and resisted strong precipitation. The 40 cm thick solidified sludge acted as an impermeable layer and yielded a good water-blocking effect. This study provides data support the application and technical advancement of solidified sludge as a landfill cover material.

The environmentally friendly magnesium oxychloride cement (denoted as MOC thereinafter) shows promising application prospects. Meanwhile, more emphasis is being paid to the environmental issues created by CO2 emissions. In this paper, carbonation-composite solidification technology is adopted to introduce MOC-lime cementitious material into sludge solidification. The effects of initial water content (H2O/MgCl2 molar ratio), lime content, MgO/MgCl2 molar ratio, and carbonation time on the mechanical properties and micromechanisms of sludge solidification were investigated using unconfined compressive strength (UCS), pH value, carbonation depth, mass loss rate, scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The results show that the UCS of sludge solidification decreases with an increase in H2O/MgCl2 molar ratio, and increases first and then decreases with an increase in lime content, reaching a maximum value at H2O/MgCl2 molar ratio of 24.3 and lime content of 4 %. Notably, carbonation significantly improves the UCS of the samples, and with an increase in carbonation time, the mass loss rate and carbonation depth increase, while the pH value decreases. Additionally, uncarbonated samples show an increase in compressive strength with an increase in MgO/MgCl2 molar ratio, as the hydration products gradually transform from amorphous gel to crystalline phases 3, phases 5, and brucite (Mg(OH)2). Finally, XRD and SEM results indicate that the underlying mechanism for the significant improvement in strength and microstructure of the samples after carbonation is the formation of a block-like crystalline network with good binding ability, consisting of chlorartinite, nesquehonite, calcium carbonate, and C-S-H gel. This study promotes the use of MOC-based gel materials as a green stabilizer for sludge solidification, and the carbonation technique employed can improve the mechanical properties of solidified soil and significantly reduce the curing time.

In order to investigate the influence of the CaO and fly ash (FA) dosage and proportion on the mechanical properties, durability, and microstructure of solidified sludge, freeze-thaw (F-T) cycles and dry-wet (D-W) cycles are conducted to study the change in appearance and the strength attenuation of CaO-FA solidified sludge. Low-field nuclear magnetic resonance (LF-NMR) is used to analyze the microstructure of the solidified sludge with various dosages and ratios of CaO-FA. The results demonstrate that the unconfined compressive strength (UCS) and direct shear strength of solidified sludge increase with the prolongation of the curing age. Furthermore, the mechanical properties of solidified sludge are improved as the ratio of CaO-FA increases. As the curing age increases, the distribution of transverse relaxation time (T2) becomes narrow, the spectral area decreases, and the amplitude of the LF-NMR signal shows a downward and leftward tendency. Additionally, with the increase in the number of F-T cycles and D-W cycles, the UCS of solidified sludge declines and the degree of pore deterioration increased gradually. This study offers a theoretical foundation and empirical data for the dredging and treatment of sludge in cold regions.