Alkali-activated concrete (AAC) is a focal point in green building material research due to its low carbon footprint and superior performance. This study seeks to enhance the impact resistance of recycled aggregate concrete (RAC) by elucidating the synergistic mechanisms of alkali activation, nano-modification, and fiber reinforcement. To this end, four mix designs, incorporating NaOH and NaOH-Na2SiO3 systems with 2 % nano-SiO2(NS), were developed and assessed through setting time, compressive strength, drop hammer impact tests, and XRD/ SEM analyses. The NaOH-Na2SiO3 system exhibited a 23.5 % increase in compressive strength over NaOH, achieving 28.41 MPa, while NS refined pore structures, elevating strength to 32.2 MPa; XRD/SEM analyses confirmed mechanisms of pore refinement and interfacial enhancement. In the optimized system, the NT12-C5 formulation, incorporating polypropylene fiber (PPF) and recycled carbon fiber (RCF), exhibited superior impact resistance, with NS enhancing interfacial bonding between carbon fiber and the matrix, resulting in a 47.8 % increase in initial crack impact energy. The Weibull model validated the reliability of impact performance. Furthermore, life cycle assessment revealed that Soil Solidification Rock Recycled aggregate concrete (SSRRAC) substantially reduced carbon emissions compared to ordinary Portland cement (OPC), while maintaining competitive economic costs. This study's innovations include: (1) synergistic optimization of low-carbon AAC performance using NaOH-Na2SiO3 and NS; (2) optimized PPF/RCF formulations promoting the reuse of waste carbon fiber; and (3) application of the Weibull model to overcome conventional statistical constraints. Collectively, these findings establish a theoretical and practical foundation for the global development of sustainable building materials.

The increasing production of waste glass fiber reinforced polymer (GFRP) is causing severe environmental pollution, highlighting the need for an effective treatment method. This study explores recycling waste GFRP powder to substitute ground granulated blast furnace slag (GGBS) in synthesizing geopolymers, aiming to rapidly stabilize clayey soil. The impact of GFRP powder replacement, alkali solution concentration, alkaline activator/precursor (A/P) ratio, and binder content on the geomechanical properties and permeability of stabilized soil was thoroughly examined. The findings revealed that replacing GFRP powder from 20 wt% to 40 wt% lowered the unconfined compressive strength (UCS). However, soil stabilized with 30 wt% GFRP powder displayed the highest shear strength. This indicates that the incorporation of an appropriate amount of GFRP powder elevates clay cohesion. Furthermore, an increase in GFRP powder replacement improved permeability coefficient in the early stages, with minimal impact observed after 28 days. Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) analysis revealed a microstructural evolution of the stabilized soil, transitioning from a porous to a denser, more homogeneous composition over the curing period, which can be attributed to the formation of cluster gels enveloping the soil particles. Life cycle assessment (LCA) analysis indicated that the GFRP powder/GGBS geopolymer presents an alternative option to traditional Ordinary Portland Cement (OPC) binder, featuring a global warming potential (GWP)/strength ratio reduction of 6 %-40 %. This research offers a practical solution for effectively utilizing GFRP waste in a sustainable manner, with minimal energy consumption and pollution, thereby contributing to the sustainable development of soil stabilization.

Photovoltaic panels (PVPs) in grasslands are arranged in such a way that they capture rainfall, which subsequently drips from the edges and causes splash erosion in the grassland, ultimately destroying the natural ecological environment. As such, PVPs can adversely affect fragile saline-alkali habitats, but the precise ecological impact of PVP-caused rainfall splash erosion on saline-alkali grassland has yet to be quantified. To explore the impact of splash erosion on the saline-alkali grassland under PVPs, an investigation was performed here on various surfaces commonly underneath PVPs. These surfaces were typical bare saline-alkali surface (B), Suaeda glauca surface (S) and Leymus chinensis surface (L), and all were positioned under PVPs in the Songnen Plain saline-alkali grassland. The soil splash erosion ditch morphology, the plant community status, and the field-measured soil properties of the three underlying surfaces were all analyzed as part of this investigation in accordance with the observed impact of splash erosion on the three underlying surface ecosystems. Ultimately, the splash erosion generated four ditches in the underlying surfaces, with the degree of soil loss ranked from greatest to smallest as B > S > L. According to the RDA results, vegetation coverage was the main factor affecting splash ditch morphology. The vegetation of the S. glauca surface was fragmented following splash erosion. Much of the S. glauca in the splash erosion ditch died, resulting in a 33.47 %-64.66 % reduction in coverage. In contrast, L. chinensis maintained a higher coverage, which means that it inhibited splash erosion more effectively. For the bare surface, the rainfall splash reduced pH and Ec, and S. glauca began to grow along the edge of the ditch. Collectively, our study quantified the impact of rain splash erosion under PVPs in a saline-alkali grassland ecosystem, comparing the difference in the degree of splash erosion among three different underlying surfaces.

Resourceful utilisation of tailings waste remains a hotspot in global research. While silica-aluminate-rich copper tailings can serve as raw materials for geopolymer preparation, their high Si/Al ratio significantly limits the geopolymerization degree. This study investigates the feasibility of developing copper tailings-based geopolymers for road base applications, using copper tailings as the primary raw material supplemented with 30 % soft soil, 15 % fly ash, and 5 % cement. The effect of NaOH content on the strength characteristics of copper tailings-based geopolymers was explored by the unconfined compressive strength test and triaxial test. The mineral composition and microstructure of copper tailings-based geopolymers specimens were characterised based on the microscopic technique. The results show that: (1) With the increase of NaOH content, the unconfined compressive strength of the copper tailings base polymer increases and then decreases, and reach the maximum value when the NaOH content is 1 %. Compared with the sample without NaOH, the addition of 1 % NaOH increased the unconfined compressive strength by 47 % at the early stage and 69 % at 28d curing age. (2) An optimal NaOH content significantly improves the shear performance of the copper tailings-based polymer, primarily by enhancing its cohesion. Triaxial test results demonstrate that 1 % NaOH addition increases cohesion by 73 % at 28d curing age. (3) The NaOH promotes the formation of geopolymer gel, refines the pore structure, and increases sample density, thereby enhancing strength. Overall, the research results can provide a reference for the application of copper tailings solid waste in roadbed materials.

Activated coke waste (ACW), a byproduct of industrial desulfurization and denitrification, consists of fine particles ( Na+ > Cl-. Isothermal adsorption analysis revealed that Na+ and Cl- adsorption aligned with the Langmuir model, whereas SO42- adsorption adhered to the Freundlich model. Application of SACW (>= 10 g kg(-1)) effectively improved saline-alkali soil properties by lowering pH and salinity, enhancing soil aggregate stability, and promoting nutrient utilization efficiency. Notably, SACW-treated soils supported maize plants with significantly increased height and biomass (13.94% and 159.28% higher, respectively; P <= 0.05) compared to untreated controls. These benefits stemmed from improved nutrient availability and reduced salt stress-induced plasma membrane damage. These findings validate SACW as a sustainable, functional amendment for reclaiming saline-alkali ecosystems and boosting crop productivity.

To address scour hazards surrounding offshore foundations, a new method employing novel alkali-activated cementitious grout (AACG) has been proposed for improvement of seabed soil. Ground granulated blastfurnace slag (GGBFS) was replaced by fly ash (FA), steel slag (SS) or FA + SS to prepare precursors, the replacement amounts were 10 %, 20 %, 30 % and 40 %. Fresh-state and mechanical properties, minerals and microstructures were investigated. A novel scour simulation test device was developed to simulate engineering conditions of scour and remediation. Flow-soil coupled scour resistance tests were conducted, shear tests and SEM measurements of solidified soil were carried out. The results showed that the optimal ratio of GGBFS:FA:SS was 6:2:2 for AACG. The optimized AACG has better fluidity and lower brittleness, and its 28 d unconfined compressive strength (UCS) achieves 13.5 MPa. For AACG solidified soil, the maximum scour depth was reduced by 33.3 % and the maximum sediment transport amount was decreased by 53.2 %, which were compared to those of cement - sodium silicate (C-S) double slurry. Moreover, the increase degrees of internal friction angle, cohesion and critical shear stress were 700 %, 7.9 % and 786 %, respectively. The scour resistance of AACG solidified soil was superior. The inherent relationship between UCS and critical shear stress was discussed. UCS can be used to rapidly assess the scour resistance of consolidated soil. This study introduced an eco-friendly AACG as an innovative stabilizer for soil reinforcement around offshore structural foundations, offering significant application and environmental values for scour control.

Research on the performance of solidified soil in capillary water absorption seawater environments is necessary to reveal the durability under conditions such as above seawater level in coastal zones. Taking soda residue-ground granulated blast furnace slag-carbide slag (SR-GGBS-CS) and cement as marine soil solidifiers, the deterioration characteristics of solidified soil resulting from capillary seawater absorption were elucidated systematically through a series of tests including capillary water absorption, unconfined compressive strength, swelling, local strain, and crystallization. The microscopic mechanism was analysed through nuclear magnetic resonance and X-ray diffraction tests. The results showed that cement-solidified soil exhibited higher water absorption and faster swelling compared with SR-GGBS-CS solidified soil in the one-dimensional seawater absorption state. In the three-dimensional seawater absorption state, solidified soil with low GGBS dosage experienced a significant transition from vertical shrinkage to swelling during the capillary water absorption process, leading to a substantial decrease in strength after 7 days of crystallization. Cement-solidified soil displayed non-uniform and anisotropic swelling, along with the formation of more external salt crystals. Overall, the soil solidified with 25% SR, 10% GGBS, and 4% CS demonstrated robust resistance to capillary absorption deterioration in a seawater environment due to its minimal water absorption and swelling, uniform surface strain, weak salt crystallization, and limited strength deterioration caused by capillary water absorption.

Although significant theoretical and technological advancements have been made in the application of concrete in saline soil regions over the past two decades, newly constructed reinforced concrete structures in these areas still face severe issues of corrosion and degradation. This is due to the complex deterioration environment in saline soil regions, characterized by the combined effects of salt corrosion, dry-wet cycles, and freeze-thaw conditions. The reduced service life of concrete structures in this region is closely related to the diffusion and distribution patterns of high-concentration chloride salts and various corrosive ions within the concrete. These patterns affect the content, transformation, and microstructure of corrosion products, ultimately leading to a shorter service life compared to other environments. This paper simulates the saline-alkali soil environment using solutions of different concentrations of chloride sulfates and magnesium salts, studies the diffusion and distribution patterns of chloride ions and sulfate ions in concrete under this environment, and analyzes the mechanism of action in conjunction with changes in microstructure. The experimental system adopts a dry-wet cycle test that can represent the characteristics of the semi-arid continental climate in Western China. The results show that although the content of free chloride ions and total chloride ions entering the concrete in the saline-alkali soil simulation solution is the lowest, the binding capacity of chloride ions is significantly greater than that of sulfate ions and far exceeds that in other environments. Under the action of high-concentration chlorides alone, the content of chloride ions in concrete is the highest, and the binding capacity of chloride ions also increases with the concentration of chlorides. The content of free sulfate ions and total sulfate ions entering the concrete in the saline-alkali soil simulation solution and their binding capacity are higher than in the control solution. Due to the ability of sulfate ions to hinder the diffusion of chloride ions in concrete, magnesium ions play a hindering role in the early stage and an accelerating role in the later stage. This results in concrete corroded by the saline-alkali soil environment, which has a characteristic of low chloride ion content and high sulfate ion content. The ions in the saline-alkali soil solution that cause concrete damage are Cl-, SO42-, and Mg2+. These ions react with the concrete to form Friedel's salt, Aft and AFm phase calcium aluminate, gypsum, Mg-S-H, and Mg(OH)2, among other substances. These corrosion products significantly impact the microstructure of concrete, causing the microstructure of concrete to transition from dense to loose to cracked much earlier than in other environments.

Saline-alkaline stress is a common problem in Akebia trifoliata cultivation. In this study, the enhancing effects of 5-azacytidine (5-AzaC) on the resistance of A. trifoliata to saline-alkaline stress and the underlying mechanisms were investigated. Plant height, stem diameter, biomass, root length, fresh weight of root, and root/shoot ratio of 6-month-old A. trifoliata seedlings were measured after saline-alkaline stress with or without 5-AzaC treatment. Moreover, the contents of photosynthetic pigments, malondialdehyde (MDA), H2O2, sodium, soluble sugar, and proline; activities of superoxide dismutase, peroxidase (POD), and catalase (CAT); and anatomical structures of root, stem, and leaf were assessed. Furthermore, comparative transcriptome sequencing was performed. The results demonstrated that growth and development of A. trifoliata were severely inhibited under saline-alkaline stress, suggesting that the seedlings were exposed to severe oxidative and osmotic stresses. Treatment with exogenous 5-AzaC could significantly relieve the symptoms of saline-alkaline stress in A. trifoliata. Under saline-alkaline stress, 5-AzaC could increase the stem diameter, biomass, root length, fresh weight of root, and root/shoot ratio and minimize damages to the anatomical structure. Moreover, absorption of Na+ was reduced; ionic balance was maintained; POD and CAT activities were significantly improved; proline and soluble sugar contents increased, and H2O2 and MDA contents decreased. Transcriptome analysis revealed that 5-AzaC functioned via regulating KEGG pathways such as plant hormone signal transduction, phenylpropanoid biosynthesis, photosynthesis, amino sugar and nucleotide sugar metabolism, and glutathione metabolism under saline-alkaline stress. Particularly, enhanced expression of genes from the auxin pathway in plant hormone signal transduction; the lignin synthetic pathway in phenylpropanoid biosynthesis; and photosystem II, photosystem I, photosynthetic electron transport, and F-type ATP pathway in photosynthesis may be related to 5-AzaC-induced saline-alkaline resistance. The results provided theoretical references for A. trifoliata cultivation in saline-alkaline soil and application of 5-AzaC to improve saline-alkaline tolerance in plants.

Alkali-activated materials have gained increasing popularity in the field of soil barrier materials due to their high strength and low environmental impact. However, barrier materials made from alkali-activated materials still suffer from long setting times and poor barrier performance in acidic, alkaline, and saline environments, which hinders the sustainable development of green alkali-activated materials. Herein, coconut shell biochar, sodium silicate-based adhesives, and polyether polyol/polypropylene polymers were used for multi-stage material modification. The modified materials were evaluated for barrier performance, rapid formation, and resistance to acidic, alkaline, and saline environments, using metrics such as compressive strength, permeability, mass loss, and VOC diffusion efficiency. The results indicated that adhesive modification reduced the material's setting time from 72 to 12 h. Polymer modification improved resistance to corrosion by 15-20%. The biochar-containing multi-stage modified materials achieved VOC diffusion barrier efficiency of over 99% in both normal and corrosive conditions. These improvements are attributed to the adhesive accelerating calcium silicate hydration and forming strength-enhancing compounds, the polymer providing corrosion resistance, and biochar enhancing the volatile organic compounds (VOC) barrier properties. The combined modification yielded a highly effective multi-stage green barrier material suitable for rapid barrier formation and corrosion protection. These findings contribute to evaluating multi-level modified barrier materials' effectiveness and potential benefits in this field and provide new insights for the development of modified, green, and efficient alkali-activated barrier materials, promoting the green and sustainable development of soil pollution control technologies.