Search Results (28)

Fluidized solidified soil (FSS) has emerged as a promising material for marine pile scour remediation, yet its limited construction window and vulnerability to hydraulic erosion before sufficient curing constrain its broader application. This study systematically evaluates FSS formulations based on dredged sediment, cement partially replaced by silica fume (i.e., 0%, 4%, 8%, and 12%), and quicklime activation under three water–solid ratios (WSR, i.e., 0.525, 0.55, and 0.575). Experimental assessments included flowability tests, unconfined compressive strength, direct shear tests, and microstructural analysis via XRD and SEM. The results indicate that SF substitution significantly mitigates flowability loss during the 90–120 min interval, thereby extending the operational period. Moreover, the greatest enhancement in mechanical performance was achieved at an 8% SF replacement: at WSR = 0.55, the 3-day UCS increased by 22.78%, while the 7-day cohesion and internal friction angle rose by 13.97% and 2.59%, respectively. Microscopic analyses also confirmed that SF’s pozzolanic reaction generated additional C-S-H gel. However, the SF substitution exhibits a pronounced threshold effect, with levels above 8% introducing unreacted particles that disrupt the cementitious network. These results underscore the critical balance between flowability and early-age strength for stable marine pile scour repair, with WSR = 0.525 and 8% SF substitution identified as the optimal mix. Full article

Traditional landfill cover materials have low strength and poor dry–wet durability. Municipal solid waste incineration fly ash (MSWI FA) can be used to partially replace cement solidification dredging sediment (DS). This article investigates the possibility of using MSWI FA and ordinary Portland cement (OPC) composite cured DS as a covering material. The mechanical properties, permeability, and wet–dry durability of the cured system were investigated under the conditions of MSWI FA content ranging from 0% to 60% and OPC content ranging from 10% to 15%. The microscopic mechanism was analyzed by scanning electron microscopy and X-ray diffraction. The results showed that when the OPC and MSWI FA contents were 15% and 20%, respectively, the comprehensive performance of the cured specimens was best after 28 days of natural curing. The unconfined compressive strength reached 1993.9 kPa, and the permeability coefficient decreased to below 1 × 10⁻⁷ cm/s, fully meeting the requirements for landfill coverage. C-S-H gel is the main strength source of the solidified body, while Friedel salt and ettringite enhance the compactness of the matrix. An excessive moisture environment promotes the water absorption of soluble salts produced by MSWI FA hydration, leading to sample expansion and reduced strength. MSWI FA and OPC cured DS exhibit good compression performance in the intermediate cover system of landfills, and can maintain good engineering performance under periodic dry–wet cycles. This dual strategic synergy solves the hazardous disposal problem of MSWI FA and the resource utilization demand of DS, demonstrating enormous application potential. Full article

Stabilized/solidified (S/S) sediments are eroded by dry–wet cycles (DWs) when applied in an atmospheric environment. The microporous structures of S/S sediments, including their size, shape, and distributions, are sensitive to DWs and closely related to their macro properties. Therefore, multiscale micropore measurements, including scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and nitrogen adsorption porosimetry (NAP), were conducted on S/S sediment samples subjected to different DWs to elucidate the micro-damage mechanisms of S/S sediments under DWs, in conjunction with unconfined compression strength (UCS) tests. The results indicated that, as DWs increased, the strength of the S/S sediments decreased, and pores/cracks developed due to the expansion of the calcium silicate hydrate (CSH) skeleton pore structures and the shrinkage of the sediment aggregate pore structures. Pores that accounted for most of the volume were those in the sediment aggregates in the range of 10² nm < d < 10⁴ nm (d represents the pore diameter), while smaller pores in the range of d < 10² nm contributed 90% of the pore area. Pores in the CSH skeletons (d > 10⁴ nm) increased with DWs, while those in the sediment aggregates decreased with DWs due to the expansion and shrinkage forces originating from the sediment particles with pore sizes of d < 10 nm. The plastic deformation of the pores in the CSH skeletons and sediment aggregates jointly controlled the strength of S/S sediments, and the adjustment of those pores gradually reduced the decrease rate of UCS. The revealed damage mechanisms of S/S during DWs provide theoretical foundations for optimizing S/S additives and expanding the engineering applications of the S/S sediments. Full article

This study investigates efficient dehydration and solidification techniques for waste mud generated from loess pile foundations during highway construction in Lanzhou, Northwest China. The waste mud, characterized by high viscosity (85% moisture content) and alkalinity (pH 11.2), poses environmental risks if untreated. Dehydration experiments identified an optimal composite flocculant mixture of 3.5 g polyaluminum chloride (PAC) and 22 mL anionic polyacrylamide (APAM) per 500 mL waste mud, accelerating sedimentation and reducing the supernatant pH to 8.65, compliant with discharge standards. Solidification tests employed a composite curing agent (CG-T1+cement), demonstrating enhanced mechanical properties. The California Bearing Ratio (CBR) of the solidified sediment reached 286%, and the unconfined compressive strength (UCS, 7-day) exceeded 2.0 MPa, meeting roadbed specifications. The combined use of PAC-APAM for dehydration and CG-T1–cement for solidification offers an eco-friendly and economically viable solution for reusing treated waste mud in construction applications, addressing regional challenges in mud disposal and resource recovery. Full article

(1) Background: The construction industry continuously seeks sustainable alternatives to traditional materials for subgrade material in pavement construction, aiming to mitigate environmental impact while maintaining performance standards. This study investigates the feasibility of incorporating phosphogypsum (PG) and contaminated sediment into subgrade materials, focusing on their physico-chemical and physico-mechanical properties. (2) Methods: The physico-chemical and physico-mechanical properties, performance, and mechanisms of solidified sediment with phosphogypsum (3% and 5% of phosphogypsum in mixture) were studied using long-term leaching tests (ANS 16.1), uniaxial compressive strength (UCS), California Bearing Ratio (CBR), X-ray fluorescence (XRF), and thermogravimetric analysis (TGA). (3) Results: Based on the pseudo-total metal content (Cr, Ni, Cu, Zn, As, Cd, Pb), the sediment is classified as third- and fourth-class, indicating it is polluted and requires treatment before disposal in the environment. To assess the long-term behavior of the sediment treated with phosphogypsum (S/S), a semi-dynamic ANS 16.1 leaching test was performed. The results showed that the metals exhibit moderate mobility, with average diffusion coefficients (De) ranging from 10⁻⁸ cm²/s for Zn (in both mixtures) to 10⁻¹² cm²/s for Cr (in mixture F-3). The leaching index (LX) values for both mixtures were above 9 for most metals, confirming their suitability for “controlled” use. Granulometric analysis indicated a predominance of fine particles, which enhances the material’s plasticity and mechanical properties. Atterberg consistency tests showed that increasing phosphogypsum content improved both the Liquid Limit and Plastic Index. However, UCS tests indicated that neither the 3% nor 5% phosphogypsum mixtures met the minimum strength requirements for subgrade material. On the other hand, CBR values demonstrated promising performance, with 12.5% for the 3% phosphogypsum mixture and 22.9% for the 5% phosphogypsum mixture. Overall, phosphogypsum positively influenced the strength development of the sediment-PG mixtures, as confirmed by XRF and TGA analyses. (4) Conclusions: Environmental considerations, such as leachability of contaminants, were investigated to ensure the sustainability of the proposed subgrade materials. Leaching tests indicated minimal pollutant release, suggesting the potential for safe utilization of PG and sediment in subgrade material. This study provides valuable insights into the physico-chemical and physico-mechanical properties of pavement mixes incorporating PG and sediment, supporting the feasibility of using these alternative materials in sustainable subgrade material for pavement construction and offering a viable solution to mitigate waste generation while enhancing pavement performance. Full article

This study presents the results of investigating the interaction between the CeF₃–EuF₃ system and the NaCl–KCl salt melt using spectroscopic methods. It was found that CeF₃ ions undergo no significant changes upon dissolution in the NaCl–KCl melt. In contrast, the dissolution of EuF₃, both individually and within the CeF₃–EuF₃ system, is accompanied by redox reactions leading to the formation of Eu²⁺. The diffuse reflectance spectra of both the bottom (insoluble sediment) and upper parts of the solidified salt melt in the UV range indirectly indicate photoluminescence excitation from Ce³⁺ and Eu²⁺ ions. In addition, absorption bands in the near-IR region (1900–2300 cm⁻¹) confirm the retention of some Eu³⁺ ions in the salt melt. The study explored the effects of various factors—including sample composition, excitation wavelength, prior and subsequent heat treatment, and medium composition—on the excitation and emission spectra of the samples. Intense 5d-4f luminescence of Ce³⁺ and Eu²⁺ ions (at 330 and 430 nm, respectively) was observed predominantly in the upper part of the salt melts, along with much weaker 4f-4f luminescence from Eu³⁺ ions. Certain parameters were optimized to reduce the luminescence contribution from Ce³⁺ and especially Eu³⁺ ions while enhancing the luminescence of Eu²⁺ ions. Solidified salt solution-melts of the NaCl–KCl–CeF₃–EuF₃ system show promise as materials for developing solar ultraviolet radiation detectors. Full article

Engineering sludge, industrial waste, and construction waste are marked by high production volumes, substantial accumulation, and significant pollution. The resource utilization of these solid wastes is low, and the co-disposal of multiple solid wastes remains unfeasible. This study aimed to develop an effective impermeable liner material for landfills, utilizing industrial slag (e.g., granulated blast furnace slag, desulfurized gypsum, fly ash) and construction waste to consolidate lake sediment. To assess the engineering performance of the liner material based on solidified lake sediment presented in landfill leachate, macro-engineering characteristic parameters (unconfined compressive strength, hydraulic conductivity) were measured using unconfined compression and flexible wall penetration tests. Simultaneously, the mineral composition, functional groups, and microscopic morphology of the solidified lake sediment were analyzed using microscopic techniques (X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy + energy dispersive spectroscopy). The corrosion mechanism of landfill leachate on the solidified sediment liner material was investigated. Additionally, the breakdown behavior of heavy metal Cr(VI) within the solidified sediment liner barrier was investigated via soil column model experiments. The dispersion coefficient was computed based on the migration data of Cr(VI). Simultaneously, the detection of Cr(VI) concentration in pore water indicated that the solidified sediment liner could effectively impede the breakdown process of Cr(VI). The dispersion coefficient of Cr(VI) in solidified sediments is 5.5 × 10⁻⁶ cm²/s–9.5 × 10⁻⁶ cm²/s, which is comparable to the dispersion coefficient of heavy metal ions in compacted clay. The unconfined compressive strength and hydraulic conductivity of the solidified sediment ranged from 4.90 to 5.93 MPa and 9.41 × 10⁻⁸ to 4.13 × 10⁻⁷ cm/s, respectively. This study proposes a novel approach for the co-disposal and resource utilization of various solid wastes, potentially providing an alternative to clay liner materials for landfills. Full article

The routine dredging of waterways produces huge volumes of sediments. Handling contaminated dredged sediments poses significant and diverse challenges around the world. In recent years, novel and sustainable ex situ remediation technologies for contaminated sediments have been developed and applied. This review article focuses on cement-based binders in stabilizing contaminants through the stabilization/solidification (S/S) technique and the utilization of contaminated sediments as a resource. Through S/S techniques, heavy metals can be solidified and stabilized in dense and durable solid matrices, reducing their permeability and restricting their release into the environment. Industrial by-products like red mud (RM), soda residue (SR), pulverized fly ash (PFA), and alkaline granulated blast furnace slag (GGBS) can immobilize heavy metal ions such as lead, zinc, cadmium, copper, and chromium by precipitation. However, in a strong alkali environment, certain heavy metal ions might dissolve again. To address this, immobilization in low pH media can be achieved using materials like GGBS, metakaolin (MK), and incinerated sewage sludge ash (ISSA). Additionally, heavy metals can be also immobilized through the formation of silicate gels and ettringites during pozzolanic reactions by mechanisms such as adsorption, ion exchanges, and encapsulation. It is foreseeable that, in the future, the scientific community will increasingly turn towards multidisciplinary studies on novel materials, also after an evaluation of the effects on long-term heavy metal stabilization. Full article

MgO carbonization is a green and low-carbon soil improvement technology. The use of MgO carbonization to solidify dredged sediment and transform it into road-building materials has significant environmental sustainability advantages. A series of microscopic characterization tests, including X-ray Diffraction (XRD), Scanning Electron Microscope–Energy Dispersive Spectrometer (SEM-EDS), and Mercury-in-Pressure (MIP) tests, were conducted to elucidate the evolution characteristics of mineral composition, microscopic morphology, and pore structure of sediment under carbonation. Based on the results, the mechanism of MgO carbonation–solidification of dredged sediment was explored. In order to verify the improvement of carbonation on the road performance of sediment, comparative tests were carried out on sediment, non-carbonated sediment, and carbonated sediment. The results indicate a significant improvement in the solidification of MgO-treated sediment through carbonation, with enhanced macroscopic strength and densified microscopic structure. This can be attributed to the encapsulation, cementation, and pore-filling effects of the hydration products and carbonation products of MgO on soil particles. The rebound modulus and splitting strength of carbonated sediment were 3.53 times and 2.16 times that of non-carbonated sediment, respectively. Additionally, the carbonated sediment showed improved saturated stability, resistance to salt solution wet–dry cycles, and resistance to freeze–thaw cycles. Full article

River and lake dredging projects inevitably produce significant quantities of wastewater and sediment. This accumulation results in dredged soil with high moisture content, characterized by low strength, rendering it unsustainable for use. To facilitate environmentally friendly utilization of wastewater and sediment, solidifying agents and basalt fibers are introduced to solidify the wastewater within the dredged sediment. This process transforms the wastewater, sediment, solidifying agents, and basalt fibers into a novel, strengthened material. This transformation allows for their application as stabilized soil for engineering endeavors. Indoor experiments and scanning electron microscope analyses were performed to examine the deformation characteristics of fiber-stabilized soil and analyze its micro-mechanisms. Research findings suggest that as the curing age increases, the curing agent’s reaction becomes more comprehensive. Fibers have the potential to ameliorate soil damage. The proposed binary-medium model’s applicability and accuracy were validated through the analysis of triaxial test results employing the reinforcement principle. These findings establish a theoretical foundation for the resourceful utilization of wastewater and sediment. Full article

In the past, due to improper sludge treatment technology and the absence of treatment standards, some municipal sludge was simply dewatered and then sent to landfills, occupying a significant amount of land and posing a serious threat of secondary pollution. To free up land in the landfill area for the expansion of a large-scale wastewater treatment plant (WWTP) in Shanghai, in this study, we conducted comprehensive pilot research on the entire chain of landfill sludge reprocessing and resource utilization. Both the combination of polyferric silicate sulfate (PFSS) and polyetheramine (PEA) and the combination of polyaluminum silicate (PAS) and polyetheramine (PEA) were used for sludge conditioning before dewatering, resulting in dewatered sludge with approximately 60% moisture content. The combined process involved coagulation and sedimentation, flocculation, and oxidation to treat the leachate generated during dewatering. The treatment process successfully met the specified water pollutant discharge concentration limits for the leachate, with the concentration of ammonia nitrogen in the effluent as low as 15.6 mg/L. Co-incineration in a power plant and modification were applied to stabilize and harmlessly dispose of the dewatered sludge. The coal-generating system ran stably, and no obvious problems were observed in the blending process. In the modification experiment, adding 5% to 7% of the solidifying agent increased the sludge bearing ratio by 53% and 57%, respectively. This process effectively reduced levels of fecal coliforms and heavy metals in the sludge but had a less noticeable effect on organic matter content. The modified sludge proved suitable for use as backfill material in construction areas without requirements for organic matter. The results of this study provide valuable insights for a completed full-scale landfill sludge reclamation and land resource release project. Full article

The decomposition of hydrates can cause serious sand production and collapse problems, hindering the long-term effective production of hydrates. This study proposes a theory for framework reconstruction and reinforcement for deep-water hydrate layers based on grouting fracturing technology and chemical sand control principles. The setting liquid was injected via fracturing and grouting to form several cracks with a certain depth and width. The setting liquid remains in the fracture and solidifies to form a “reconstruction body.” Simultaneously, the setting liquid permeates and diffuses from the cracks to the surrounding hydrate layer, bonding with the sediment and forming a gradient solidification zone to achieve solidification and reinforcement of the hydrate layer. To achieve effective production of hydrates, the reconstruction body must consider internal reinforcement, sand control, and good permeability. The parameters of the reconstruction body were designed based on the geological characteristics of hydrate formation in a certain area. In order to effectively support the hydrate layer, the reconstruction body was designed with a 24 h compressive strength of at least 3.20 MPa and a long-term compressive strength of at least 17.70 MPa. To ensure that the permeability characteristics of the reconstructed body meet production needs, the permeability of the reconstructed body must be greater than that of the hydrate layer. The maximum concentrated pore size of the skeleton reconstruction body is designed to be 9 μm based on the particle characteristics of shale sand in hydrate reservoirs. This study provides a new approach to solving sand production and collapse. Full article

Occupation of land and damage to the surrounding ecosystem may occur due to the accumulation of dredged lake sediments. In order to solve the large amount of dredged lake sediments, industrial wastes (slag, desulfurization gypsum) and urban construction waste were used to solidify the lake substrate, obtained a new construction material. Water content, volumetric shrinkage, unconfined compressive strength and flexural strength parameters and hydraulic conductivity coefficients of the solidified sediment were obtained from water content determination tests, volumetric shrinkage tests, unconfined compressive strength tests, flexural tests and permeation tests. Mineralogical composition and microstructural characterization of the solidified sediment using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were obtained. The solidification mechanism of lake sediment under the coupling of industrial waste and urban construction waste was revealed. The water content of the specimens decreased rapidly, and shrinkage deformation occurred in curing for 7 d. The volumetric shrinkage of 28 d was eventually maintained at 1.27–5.19%. The trend of specimen strength changed with the extension of time in the overall increase state, the compressive strength and flexural strength within 28 d were 3.15–10.96 MPa and 0.64–2.69 MPa, respectively. The solidified sediment material showed excellent anti-seepage performance, the hydraulic conductivity reached stability at 1.22 × 10⁻⁸–55.4 × 10⁻⁸ cm/s. Gismondine, gypsum, calcite, scawtite and fibrous C-S-H phases were generated in the solidified material. Full article

To optimize the workflow of civil engineering construction in a harbour, this paper developed a framework of the contaminant leaching assessment carried out on the stabilized/solidified dredged soil material. The specimens included the sampled sediments collected from the in situ fieldwork in Arendal and Kongshavn. The background levels of the concentration of pollutants were evaluated to assess the cumulative surface leaching of substances from samples over two months. The contamination of soil was assessed using a structured workflow scheme on the following toxic substances, heavy metals—As, Pb, Cd, Cr, Hg, Ni, and Zn; organic compounds—PAH-16 and PCB; and organotin compounds—TBT. The numerical computation and data analysis were applied to the results of geochemical testing creating computerised solutions to soil quality evaluation in civil engineering. Data modelling enabled the estimation of leaching of the contaminants in one year. The estimated leaching of As is 0.9153 mg/m², for Ni—2.8178 mg/m², for total PAH-16 as 0.0507 mg/m², and for TBT—0.00061 mg/m² per year. The performance of the sediments was examined with regard to permeability through a series of the controlled experiments. The environmental engineering tests were implemented in the Swedish Geotechnical Institute (SGI) in a triplicate mode over 64 days. The results were compared for several sites and showed that the amount of As is slightly higher in Kongshavn than for Arendal, while the content of Cd, Cr, and Ni is lower. For TBT, the levels are significantly lower than for those at Arendal. The algorithm of permeability tests evaluated the safety of foundation soil for construction of embankments and structures. The optimized assessment methods were applied for monitoring coastal areas through the evaluated permeability of soil and estimated leaching rates of heavy metals, PHB, PACs, and TBT in selected test sites in harbours of southern Norway. Full article

Near the coast of China, a large amount of sediment is produced during construction work. In order to mitigate the environmental damage caused by sediment and enhance the performance of rubber-modified asphalt effectively, solidified silt material and waste rubber were prepared to modify asphalt, and its macroscopic properties, such as viscosity and chemical composition, were determined via a routine physical test, DSR, Fourier Transform Infrared Spectroscopy (FTIR), and Fluorescence Microscopy (FM). The results show that, with the increase in powder particles and the addition of a certain amount of hardened mud, the mixing and compaction temperature of modified asphalt can be significantly increased—still reaching the design standard. In addition, the high thermal stability and fatigue resistance of the modified asphalt were clearly better than those of the ordinary asphalt. From the FTIR analysis, rubber particles and hardened silt only exhibited mechanical agitation with the asphalt. Considering that excessive silt might result in the aggregation of matrix asphalt, the addition of an appropriate amount of hardened solidified silt material can eliminate the aggregation. Therefore, the performance of modified asphalt was optimum when solidified silt was added. Our research can provide an effective theoretical basis and reference values for the practical application of compound-modified asphalt. Therefore, 6%HCS(6:4)-CRMA have better performance. Compared to ordinary rubber-modified asphalt, the composite-modified asphalt binder has better physical properties and a more suitable construction temperature. The composite-modified asphalt uses discarded rubber and silt as raw materials, which can effectively protect the environment. Meanwhile, the modified asphalt has excellent rheological properties and fatigue resistance. Full article