There has been a growing interest in controlled low strength material CLSM due to its engineering features, such as self-leveling and early strength development, as well as it potential for utilizing industrial waste. Still, the dynamic properties on CLSM are rarely studied. This study evaluates the feasibility of red mud as a partial aggregate replacement in foamed-lightweight CLSM, incorporating high-carbon fly ash and preformed foam. We varied both the red mud contents RMc and foam volume ratio FVR within the mixtures and examined their impact on unconfined compressive strength and dynamic properties including shear modulus G and damping ratio D. The results reveal that the red mud enhances foam stability, leading to more uniform pore structures and increased porosity, which reduces bulk densities. Despite higher porosity, red mud serves as a strong alkaline activator, enhancing geopolymer reactions of high-carbon fly ash and thereby increasing both compressive strength and initial shear modulus G0. Interestingly, increasing FVR had minimal impact on the D, while higher RMcnotably increased D, highlighting its distinct role in energy dissipation. The red mud-incorporated foamed CLSM exhibits strain-dependent normalized shear modulus G/G0 comparable to that of gravel, while its D is 40-100 % higher than gravel or gravelly soil at shear strain of 1.10-5, which corresponds to typical traffic-induced vibration levels. Moreover, theoretical volumetric-gravimetric relationships are introduced to account for the combined effects of FVR and RMcon CLSM behavior. These findings demonstrate that the red mud included foamed CLSM can be utilized as advanced structural backfill material capable of effectively mitigating the vibrations induced by traffic, low-amplitude seismic events, and mechanical sources.

The environmental impact of red mud leachate, particularly from tailings ponds, has become a significant concern due to its highly alkaline nature and potential to cause widespread soil and water contamination. Addressing this issue requires effective strategies for mitigating the leakage of contaminants, such as heavy metals and hazardous alkalis, into surrounding ecosystems. This study explores the use of fly ash-modified clay liners as a solution to contain and treat red mud leachate pollutants, including heavy metals and alkalis. Macro-scale tests, such as permeation and unconfined compression tests, combined with micro-scale analyses (XRD, SEM, BET), investigate the influence of varying fly ash content on the hydraulic conductivity, mechanical properties, and microstructure of the clay liners. The findings show that fly ash significantly reduces the hydraulic conductivity of the liners, improving their effectiveness in preventing seepage. It also enhances the liners' ability to adsorb heavy metal ions and increases their mechanical strength, especially cohesion, with optimal performance at a 9 % fly ash content. The study further reveals that pozzolanic reactions in the alkaline environment of red mud lead to the formation of cementitious gel binders (C-S-H, C-A-H), which reduce pore sizes and create a denser, more impermeable structure. These improvements in both physical and chemical stability demonstrate the potential of fly ash-modified clay liners as an effective, sustainable solution for managing red mud tailings ponds. This study provides valuable support for environmental management of red mud tailings ponds and the sequestration of red mud leachate waste.

Foamed lightweight soil with red mud (FLS-RM), a new type of subgrade material commonly used in projects such as bridge backfill. In engineering applications, FLS-RM tends to crack after pouring to weaken its properties, which limits its further application, and this situation can be improved by adding fiber into FLS-RM. Thus, this study developed a new type of FLS-RM reinforced by polypropylene fibers, polyester fibers, and kenaf fibers to investigate the changes in the mechanical properties of FLS-RM and its deterioration mechanism. The experimental results showed that the mechanical properties of FLS-RM could be enhanced by the fibers, and the compressive and flexural strengths of FLS-RM specimens reinforced by polypropylene fiber reached 0.87 MPa and 0.85 MPa, respectively, when the fiber length was 12 mm and the content was 0.75 wt% and 1.00 wt%. Design Expert was used to analyze the experimental data to obtain the pattern of the effect of different fiber conditions on the strength of FLS-RM and optimal fiber conditions, and to establish the strength equation. The EDS results revealed that the red mud can be excited to generate an aluminosilicate gel filling in the skeleton under alkaline conditions. The results of the microscopic analysis indicated that the close bonding between the fibers and the matrix increased the friction and mechanical bite between the independent blocks and enhanced the strength of the specimens.

Red mud is a kind of solid waste, which can be used as engineering roadbed filler after proper treatment. Due to the special physical and chemical properties of red mud, such as high liquid limit and high plasticity index, it may affect the stability of soil. Therefore, red mud can be improved by adding traditional inorganic binders such as lime and fly ash to improve its road performance as roadbed filler. Red mud-based modified silty sand subgrade filler will be affected by dry-wet alternation caused by various factors in practical application, thus affecting the durability of the material. In order to study the strength degradation characteristics and microstructure changes of red mud, lime and fly ash modified silty sand subgrade filler after dry-wet cycle, the samples of different curing ages were subjected to 0 similar to 10 dry-wet cycles, and their compressive strength, microstructure and environmental control indexes were tested and analyzed. The results show that the sample cured for 90 days has the strongest toughness and the best ability to resist dry and wet deformation. With the increase of the number of dry-wet cycles, the mass loss rate of the sample is in the range of 6 similar to 7 %, and the unconfined compressive properties and tensile properties decrease first and then increase. There are continuous hydration reactions and pozzolanic reactions in the soil, but the degree of physical damage in the early stage of the dry-wet cycle is large, and the later cementitious products have a certain offsetting effect on the structural damage. The internal cracks of the sample without dry-wet cycle are less and the structure is dense. After the dry-wet cycle, the microstructure of the sample changed greatly, and the cracks increased and showed different forms. Through SEM image analysis, it was found that the pore structure of the sample changed during the dry-wet cycle, which corresponded to the change law of mechanical properties. After wetting-drying cycles, the leaching concentration of heavy metals in the modified soil increased slightly, but the overall concentration value was low, which was not a toxic substance and could be used as a roadbed material. The study reveals the influence of dry-wet cycle on the strength characteristics and microstructure of red mud, lime and fly ash synergistically improved silty sand, which provides a technical reference for the engineering application of red mud-based materials.

This study investigated the dynamic properties of red mud (RM)-reinforced volcanic ash (VA) by dynamic triaxial tests. The effects of stress state (dynamic stress sigma d, confining stress sigma 3), dynamic frequency (f) and load waveform (F) on the accumulative plastic strain (epsilon p) have been investigated. The findings indicate a significant influence of the stress state on epsilon p. When sigma d reaches 120 kPa, the specimens exhibit insufficient strength, leading to shear failure. As sigma 3 increases, the dynamic stresses that lead to specimen destabilization also exhibit an upward trend. The effect of f on epsilon p is limited. The epsilon p does not exhibit a clear or consistent developing pattern with increasing f. As for the F, the epsilon p exhibited by the specimens subjected to sinusoidal wave loads is less than that observed under trapezoidal wave loads. Shakedown theory classifies deformation responses into plastic shakedown, plastic creep and incremental collapse. The epsilon p curve patterns of RM-reinforced VA exhibit plastic shakedown and incremental collapse without significant plastic creep characteristics under cyclic loading. A predictive model for epsilon p under cyclic loading is established, which has good predictability. This study presents a novel application of VA and RM, offering substantial research insights into waste recycling.

This study investigates the potential application of a blend, termed GGRM, consisting of red mud (RM) and ground-granulated blast furnace slag (GGBS), for stabilizing subgrade expansive soil. RM, an industrial waste from aluminium refineries, poses environmental concerns due to its high alkalinity and presence of heavy metals. Despite its increased utilization in construction sector, research on its role in soil stabilization is limited. With this in mind, RM has been used as an activator for GGBS, to create synergy between these industrial wastes with an objective to utilize this blend for stabilization of black cotton soil (BCS). Therefore, laboratory investigations were conducted to assess the strength of BCS stabilized with GGRM comprising varying proportions of GGBS and RM (0:100, 70:30, 50:50, 30:70, and 100:0 by weight). Further, the optimal GGRM quantities were evaluated by mixing it in different proportions (5-30% by weight). This study also examined the effect of curing on strength properties and leaching behaviour and investigated the associated mechanisms through microstructural studies (XRD, XRF, SEM, and FTIR analysis). The leachate potential was assessed using ICP-OES analysis. Results indicated a maximum sevenfold improvement in unconfined compressive strength of BCS, from 131 to 920 kPa, after 28 days of curing in 70:30 combinations with 25% GGRM content. Furthermore, leaching of heavy metals from stabilized soils are within the permissible limits of hazardous waste management regulations. In conclusion, RM-activated GGBS blends emerged as a potentially sustainable binder, enhancing the strength of expansive soil for subgrade applications.

Red mud (RM) is a strongly alkaline waste residue produced during alumina production, and its high alkali and fine particle characteristics are prone to cause soil, water, and air pollution. Phosphogypsum (PG), as a by-product of the wet process phosphoric acid industry, poses a significant risk of fluorine leaching and threatens the ecological environment and human health due to its high fluorine content and strong acidic properties. In this study, RM-based cemented paste backfill (RCPB) based on the synergistic curing of PG and ordinary Portland cement (OPC) was proposed, aiming to achieve a synergistic enhancement of the material's mechanical properties and fluorine fixation efficacy by optimizing the slurry concentration (63-69%). Experimental results demonstrated that increasing slurry concentration significantly improved unconfined compressive strength (UCS). The 67% concentration group achieved a UCS of 3.60 MPa after 28 days, while the 63%, 65%, and 69% groups reached 2.50 MPa, 3.20 MPa, and 3.40 MPa, respectively. Fluoride leaching concentrations for all groups were below the Class I groundwater standard (<= 1.0 mg/L), with the 67% concentration exhibiting the lowest leaching value (0.6076 mg/L). The dual immobilization mechanism of fluoride ions was revealed by XRD, TGA, and SEM-EDS characterization: (1) Ca2(+) and F- to generate CaF2 precipitation; (2) hydration products (C-S-H gel and calixarenes) immobilized F- by physical adsorption and chemical bonding, where the alkaline component of the RM (Na2O) further promotes the formation of sodium hexafluoroaluminate (Na3AlF6) precipitation. The system pH stabilized at 9.0 +/- 0.3 after 28 days, mitigating alkalinity risks. High slurry concentrations (67-69%) reduced material porosity by 40-60%, enhancing mechanical performance. It was confirmed that the synergistic effect of RM and PG in the RCPB system could effectively neutralize the alkaline environment and optimize the hydration environment, and, at the same time, form CaF2 as well as complexes encapsulating and adsorbing fluoride ions, thus significantly reducing the risk of fluorine migration. The aim is to improve the mechanical properties of materials and the fluorine-fixing efficiency by optimizing the slurry concentration (63-69%). The results provide a theoretical basis for the efficient resource utilization of PG and RM and open up a new way for the development of environmentally friendly building materials.

To enhance the applicability of multiple solid waste road base materials in seasonally frozen soil areas and reduce the negative impact of red mud (RM) on the environment owing to its strong alkalinity, this paper utilizes untreated bayer method RM, fly ash (FA), and phosphogypsum (PG) as raw materials for preparing the road base materials. The mechanical properties, leaching characteristics, and Freeze-thaw (F-T) resistance of the materials from different solid waste systems were investigated through F-T cycle tests, unconfined compressive strength (UCS) tests, and leaching tests. The hydration, sodium solidification, and F-T deterioration mechanisms were revealed using an X-ray diffractometer and a scanning electron microscope. Results indicated that when the mix ratio of RM: FA: PG: cement was 64:28:2:6 (RFP2), the specimen exhibited the best F-T resistance. After 10 F-T cycles, the compressive strength retention rate (BDR) of the specimen was 91.43 %, and the Na+ leaching concentration was 390 mg/L, which still met the Chinese standard. The main hydration products of the material include C-S-H gel and ettringite crystals. These crystals and gels are intertwined and connected to form a dense mesh structure, which improves the material's F-T resistance and sodium solidification effect. The F-T cycle results in the expansion of cracks within the material, which leads to the destruction of the adhesion of the cementitious products, thus causing a deterioration of the strength of the specimen and the reduction of the sodium solidification effect.

A self-designed water level control system was used to simulate the collapse of a red mud dam in a dry storage yard under varying water levels. The study unveiled the distribution patterns of seepage lines, pore water pressure, soil pressure, and crack evolution in red mud dams with varying slope ratios (1:2 and 1:1) under changing water levels. Experimental findings show that the rise of the infiltration line is initially rapid, then slows down, exhibiting a lag effect. The area with the highest pore water pressure beneath the infiltration line also experiences the highest horizontal soil pressure. Under different slope ratios, the reasons for the formation of main cracks are different. When the slope ratio is 1:2, under the combined action of gravity and hydraulic forces, slope cracks are generated due to the formation of a through channel extending from the interior of the red mud dam body to the slope surface. When the slope ratio is 1:1, cracks appear at the dam crest due to the traction effect of the sliding slope below the infiltration line on the upper slope. The stress and seepage fields of red mud dams with different slope ratios were analyzed using the finite element software ABAQUS, revealing the stress and displacement distribution patterns on the dam slope surface.

The preparation of geopolymer for solidification/stabilization of heavy metal contaminated soils using industrial solid waste was a sustainable method. In this study, a binary geopolymer curing agent was synthesized from red mud and fly ash for the treatment of copper- and cadmium- contaminated soils. The changes in the properties of the cured soil were investigated by analyzing compressive strength, permeability coefficient, pH value, toxicity leaching, and the chemical forms of heavy metals. These parameters were examined under varying amounts of curing agent and curing time. The solidification mechanism of contaminated soil was revealed by microscopic experiments such as X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS). The results showed that geopolymer could significantly improved the mechanical properties and environmental safety of contaminated soil. Compressive strengths of Cu and Cd contaminated soils after 28d of curing with 30 % geopolymer were 1.27 and 1.44 MPa, the permeability coefficients were 4.2 and 3.8-6cm/s, and toxic leaching amounts of Cu2+ and Cd2+ were 4.8 and 0.21 mg/L, and pH values were 10.9 and 10.6, respectively. Geopolymer gel structures not only filled the voids between soil particles but also physically encapsulated, chemically bonded, precipitated and ion-exchanged to achieve solidification/stabilization of contaminated soils. This research provided a new technology for the management of heavy metal contaminated soil and promoted the sustainable use of industrial solid waste.