Search Results (445)

The transition toward low-carbon and resource-efficient construction materials has intensified interest in geopolymer binders incorporating industrial and post-consumer wastes. Waste glass powder (WGP), a silica-rich component of the global glass waste stream, has emerged as a promising circular-economy precursor in alkali-activated systems; however, reported durability trends remain inconsistent and are often interpreted without mechanistic integration. This review synthesises current knowledge of WGP reactivity, gel chemistry, and long-term performance through an explicit reaction–transport–ageing (R–T–A) framework that links dissolution behaviour and phase assemblage development to pore connectivity, ion ingress, and time-dependent degradation. Under alkaline activation, the amorphous structure of WGP promotes silica release, modifying Si/Al ratios and governing the formation of N-A-S-H or hybrid N-A-S-H/C-(A)-S-H gels. These reaction products determine transport characteristics and ageing evolution, which collectively control chemical resistance, chloride ingress, alkali–silica reaction-type instability, and dimensional stability. Variability across studies is shown to arise from imbalances in particle fineness, replacement level, precursor chemistry, and activator design rather than intrinsic inconsistency in WGP behaviour. The R–T–A framework clarifies how reaction completeness, pore network architecture, and long-term phase stability interact to produce system-dependent durability outcomes. WGP demonstrates strong potential as a circular-economy precursor in alkali-activated binders; however, reliable structural application requires durability-informed mix design grounded in coupled reaction–transport–ageing mechanisms and supported by extended exposure testing under realistic service conditions. Full article

By adding Ce to high-strength low-alloy steel, the effects of heating parameters and Ce on grain growth were examined through in situ observation and dynamic analysis of grain growth behavior during heating, combined with precipitated phase analysis and pinning force calculations. In situ observation of the heating process revealed the behavior of grain growth and grain boundary migration in real time, providing an intuitive and accurate illustration of the effect of Ce on grain growth behavior. The mechanism of Ce’s role in refining austenite grains was clarified. The results revealed that at 1050 °C, Ce had little effect on grain growth. Ce delayed the grain coarsening temperature from 1050–1150 °C to 1150–1250 °C, resulting in grain refinement. The predicted results from the established dynamic model were consistent with the grain growth process, demonstrating high predictive accuracy. After Ce treatment, the activation energy for grain growth increased from 172.058 to 193.703 kJ/mol, representing a 12.58% rise, rendering grain growth more difficult. Within the holding temperature range, small spherical Nb-rich (Nb, Ti)(C, N) and large rectangular Ti-rich (Nb, Ti)(C, N) existed. The addition of 0.0070% Ce delayed the dissolution of Nb-rich carbonitrides. Finer precipitated phases and high-melting-point, fine Ce₂O₂S and CeAlO₃ inclusions at grain boundaries provided greater pinning force, inhibiting grain growth. Full article

To enhance the early-age properties of steel slag cement mortar and promote the resource utilization of metallurgical solid waste, in this study, nano-SiO₂ (KH-NS) was modified using a KH550 silane coupling agent. The hydration kinetics and microstructure evolution were systematically analyzed by means of a macroscopic performance test (setting time and compressive strength) and multi-scale microscopic characterization (characterized by Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, X-ray Diffraction, Thermogravimetry-Differential Thermal Analysis, and isothermal calorimetry). The influence mechanism of its content on the early performance of the steel slag cement system was systematically studied. Research findings indicate that at a given dosage, increasing the proportion of KH-NS results in a shorter setting time for steel slag mortar. When the KH-NS dosage reaches 1.5%, the initial and final setting times of steel slag mortar decrease by 24.21% and 21.20%, respectively. The addition of KH-NS effectively enhances the compressive strength of mortar, with a particularly pronounced effect on early strength prior to 14 h of curing. At a KH-NS dosage of 1.5%, the onset of the accelerated phase of hydration heat release in steel slag cement mortar is advanced by 2.5 h. Mechanistic studies indicate that KH-NS accelerates cement hydration by promoting C₃S dissolution and C-S-H gel nucleation through interactions between surface silanol groups (Si-OH) and amino groups (-NH₂). Furthermore, KH-NS refines the pore structure via a micro-aggregate filling effect, reducing the number of harmful pores and improving the pore size distribution. KH-NS continuously consumes Ca(OH)₂ through pozzolanic reactions to generate C-S-H, with its reactivity increasing with higher dosage. Research confirms that KH-NS significantly enhances the early strength and density of steel slag mortar, providing both theoretical justification and technical support for developing low-carbon building materials based on solid waste with high dosage. Full article

To investigate the deterioration law of the mechanical properties of PVA-fiber-reinforced rubber concrete under the combined action of high-temperature and salt erosion, physical index tests, dynamic mechanical property experiments, and microstructural morphology observations were carried out on specimens subjected to different temperatures (ambient temperature, 100 °C, 300 °C) and various solution attacks (water, 5% NaCl, 5% Na₂SO₄, and 5% NaCl + 5% Na₂SO₄ mixture). The results show that, after exposure to 300 °C, the PVA fibers melt and the rubber pyrolyzes, since this temperature exceeds their melting points. A residual pore network is formed inside the matrix, and the damage degree of ultrasonic pulse velocity is about 2.3 times that of the 100 °C group. Although salt solution and its crystallization products can physically fill the pores and cause a partial recovery of pulse velocity, this change is mainly due to the alteration of the pore medium and does not represent a substantial restoration of the microstructure. The effects of different salt solutions on dynamic mechanical properties vary significantly: Sulfate erosion improves the dynamic performance significantly at ambient temperature by forming gypsum and ettringite to fill pores, but this strengthening effect disappears after 300 °C. Sodium chloride attack generates Friedel’s salt and consumes C₃A, leading to general strength deterioration. In composite salt erosion, the competitive and synergistic effects of Cl⁻ and SO₄²⁻ destabilize erosion products and weaken interfacial bonding, resulting in consistent decreases in dynamic compressive strength and elastic modulus under all temperatures and impact pressures. The strength reduction reaches 66.2% after 300 °C. Microscopic analysis confirms that composite salt erosion leads to the dissolution of ettringite and loose structure, which verifies the synergistic deterioration law of macroscopic properties. This study systematically reveals the damage evolution mechanism of PVA-fiber-reinforced rubber concrete under the coupled action of high-temperature and salt erosion, and provides a theoretical basis for the dynamic bearing capacity evaluation and durability design of concrete structures in such coupled environments. Full article

Blast furnace cement-dolomite mortars prepared from commercial cement (CEM-III/B) containing ~75% of slag and natural dolomite were aged under accelerated conditions at 60 °C in 1 M NaOH for 0–24 months. The hydration products and microstructure features of the mortars were studied using XRD, TGA and SEM-EDS methods, with blast furnace cement paste for comparison. The results showed that the presence of dolomite enhanced slag hydration, as the carbonates released during dedolomitisation promoted Ca and Si dissolution from the slag grains. After prolonged ageing, a multi-rim structure was observed around the slag particles: the inner rim primarily consisted of a hydrotalcite-like phase mixed with C-S(A)-H gel, while the outer rims were richer in C-S(A)-H gel, with varying calcium content. Monocarbonate phase was additionally detected at the slag–paste interface in the presence of dolomite. The observed increase in mechanical strength during ageing had to do with two reasons: (i) the increase in hydration product content and (ii) the densification of microstructure due to the formation of calcium carbonate, which filled pores and microcracks and the possible carbonation of C-S (A)-H gel in the binding paste. Under the investigated alkaline ageing conditions, dolomite acts as a chemically active component rather than an inert filler, influencing both slag hydration kinetics and the composition of the resulting hydration products. Full article

To promote the high-value utilization of fly ash (FA) and address the prolonged setting time and limited strength associated with conventional single-alkali activation, this study proposes a synergistic dual-alkali activation strategy using Ca(OH)₂ and Na₂SiO₃ in combination with microwave-assisted curing for low-calcium fly ash. Samples containing varying amounts of Ca(OH)₂ were systematically characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), compressive strength testing, and pore structure analysis. The results show that Ca(OH)₂ facilitates the formation of calcium aluminosilicate hydrate (C-A-S-H) gel, while Na₂SiO₃ sustains the alkaline environment and enhances the dissolution of SiO₂ and Al₂O₃ from FA. The dual-alkali synergistic system, when coupled with microwave treatment, markedly refines the pore structure, increases the degree of polymerization, and improves compressive strength from 0.5 MPa to 1.7 MPa with increasing Ca(OH)₂ content. In addition, the prepared fly ash-based geopolymer (FABG) demonstrates pronounced pH-buffering capacity in acidic environments and exhibits antibacterial activity, primarily attributable to its sustained release of alkalinity. This work highlights that integrating dual-alkali activation with microwave curing can simultaneously enhance microstructural development, chemical stability, and functional performance in low-calcium FA systems, thereby offering a viable route for the development of sustainable and multifunctional green building materials derived from industrial solid waste. Full article

This monograph evaluates the scientific and regulatory underpinnings for bioequivalence (BE) waiver of immediate-release (IR) solid oral meloxicam formulations, as a surrogate for in vivo pharmacokinetic trials. In compliance with ICH (The International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use), FDA (Food and Drug Administration), and PMDA (Pharmaceuticals and Medical Devices Agency) bioequivalence guidelines, a systematic characterization was performed on meloxicam’s critical attributes, encompassing solubility, permeability, dissolution behavior, pharmacokinetic profiles, therapeutic index, and drug-excipient compatibility. Classified as BCS Class II (low solubility, high permeability), meloxicam nonetheless exhibits a broad therapeutic window and pharmacokinetic characteristics aligning with BE Category I, thus enabling generic product approval via BE waiver with negligible risks of systemic exposure inequivalence. It is noteworthy that current in vitro methodologies are not consistently capable of capturing C_max disparities of BCS Class II weak acids. BE waiver eligibility for meloxicam IR formulations necessitates three prerequisites: (a) excipient composition identical to the reference listed drug and validated by regulatory authorities; (b) ≥85% dissolution within 30 min at pH 1.2, 4.5, and 6.8; (c) comparable dissolution profiles across these pH conditions. Non-adherence mandates a mandatory in vivo BE assessment. Full article

This study is based on isotope (δ¹⁸O, δ²H, ¹⁴C), hydrochemical, and groundwater-level data from the past 47 years in the central North China Plain (NCP). It uses methods such as mathematical statistics, Piper diagrams, Gibbs models, and ion ratios to investigate the characteristics of changes in the groundwater flow field, hydrochemistry, and isotopes across various aquifers in the Hengshui funnel area before and after the implementation of groundwater exploitation reduction measures (GWER). Furthermore, it reveals the driving mechanisms of these measures’ effects on hydrochemical characteristics and isotopic variations. The results show the following: (1) The hydrochemical type of shallow groundwater (SG) before GWER was primarily Cl▪SO₄-Na▪Ca, which diversified to Cl▪SO₄-Na and SO₄▪Cl-Na types after GWER; the deep groundwater (DG) type changed from Cl▪SO₄-Na to Cl-Na. (2) Before GWER, the hydrochemical composition of SG and DG was primarily controlled by the dissolution of silicates, salt rocks, and evaporites. After GWER, the hydrochemical composition of DG primarily originated from the dissolution of evaporites and salt rocks, accompanied by enhanced cation exchange. (3) The δ¹⁸O of SG was affected by the recharge of irrigation return water, changing from enrichment to depletion before and after the GWER. The δ¹⁸O value in DG changed from depletion to enrichment, and the groundwater age changed from older to younger after the GWER. The GWER altered the hydrodynamics, weakened the hydraulic connectivity, and led to changes in the evolution of the hydrochemistry. The findings have direct implications for water quality and promoting the sustainable utilization of deep groundwater in the NCP’s central funnel area. Full article

The cement industry is a major contributor to global CO₂ emissions, necessitating the development of low-carbon alternatives, such as alkali-activated slag cement (AAS). This study investigates the feasibility of using NaCl and NaOH as co-activators for granulated blast furnace slag (GBFS), focusing on the alkali-equivalent-dependent role of NaCl. At a low-alkali equivalent (2% Na₂O), incorporation of ≤4 wt% NaCl enhanced ionic strength, promoted slag dissolution, and accelerated C-(A)-S-H gel formation, increasing 28-day compressive strength by up to 21%. In contrast, at a high-alkali equivalent (4% Na₂O), NaCl addition induced competitive binding of Cl⁻ with aluminate species, inhibiting C-(A)-S-H formation and reducing strength by up to 18% at 10 wt% NaCl. The optimal NaCl dosage for strength improvement was 1–4 wt% under low alkalinity and 1–2 wt% under high alkalinity. Microstructural analyses (XRD, FTIR, TG-DTG, SEM-EDS) confirmed that NaCl promotes Friedel’s salt formation under both conditions, but its effect on the primary gel phase is alkalinity dependent. This work provides a theoretical basis for utilizing industrial NaCl by-products in low-carbon cement design and highlights the importance of alkalinity control in achieving synergistic activation. Full article

Calcium silicate hydrate (C(-A)-S-H) and its aluminosilicate counterpart (C-A-S-H) constitute the principal binding phases in Portland cement and blended systems, governing mechanical strength and durability. This paper presents a summary of the work related to dehydration of C(-A)-S-H and rehydration of dehydrated C(-A)-S-H. Their thermal dehydration, a key process for cement recycling, induces profound multi-scale transformations: at the atomic level, it alters calcium and aluminum coordination environments and disrupts chemical bonding; at the chain-structure level, it causes depolymerization of the silicate/aluminosilicate networks; and at the microstructural level, it leads to changes in nanoscale particle morphology, aggregation state, and pore structure, creating a metastable, defect-rich, high-energy state distinct from the original C(-A)-S-H. The subsequent rehydration of this dehydrated C(-A)-S-H, which is not a simple reversal but a distinct dissolution–precipitation process, enables microstructural reconstruction and restored reactivity upon contact with water. This rehydration capacity is fundamentally exploited in thermally activated recycled cement—a novel binder concept that leverages dehydration-induced metastability for renewed strength development. Understanding these interconnected processes, influenced by factors like temperature, humidity, rate, and aluminum content, is critical for advancing sustainable cement technology, enabling the design of high-performance recycled cement and concrete, and facilitating the recycling of cementitious materials. Full article

This study addresses the dual challenges of low copper recovery and persistent arsenic pollution in the bioleaching of low-grade, high-arsenic copper ores containing enargite (Cu₃AsS₄). Through integrated electrochemical, chemical, and biological investigations, a selective and environmentally sustainable two-stage hybrid leaching process was developed. Electrochemical analysis identified a critical oxidation threshold of ~750 mV governing enargite dissolution. Chemical leaching and X-ray Photoelectron Spectroscopy (XPS) analysis revealed a temperature-dependent sulfur transformation pathway, enabling a staged thermal strategy: flotation below 40 °C to maximize hydrophobic elemental sulfur (S⁰) formation, and bioleaching at 40–55 °C to promote complete sulfur oxidation to sulfate. Optimization produced a two-stage process comprising 10-day chemical pre-leaching with FeSO₄ (10.0 g/L Fe²⁺) followed by bioleaching, achieving 78.3% copper extraction while suppressing arsenic dissolution to approximately 10%. The use of FeSO₄ instead of Fe₂(SO₄)₃ reduces reagent costs by ~70%, saving an estimated CNY 47,250 daily at 1000 t/d scale. Leaching toxicity tests confirm residue As < 0.10 mg/L, meeting non-hazardous waste standards (GB5085.3-2007). This work provides the first integrated demonstration of electrochemical threshold control combined with temperature-dependent sulfur speciation for selective copper extraction from arsenic-bearing enargite ores, offering a scalable, reagent-economical, and environmentally sustainable metallurgical route. Full article

Under dual challenges of global infrastructure expansion and industrial solid waste management, alkali-activated polymers (AAP), as industrial solid-waste-based low-carbon cementitious materials, exhibit immense potential in grouting engineering applications. This review synthesizes current research progress through three critical dimensions: reaction mechanisms, performance characteristics, and grouting applications (grouting for reinforcement and water-blocking). The reaction mechanism universally comprises three stages: dissolution, depolymerization, and polycondensation. Key performance determinants include precursor composition (e.g., slag, fly ash, metakaolin) and alkaline activator properties (type, modulus, concentration). The multifunctional advantages of AAP are fundamentally governed by their microstructural evolution. Specifically, the rapid formation of highly cross-linked C-(A)-S-H and N-A-S-H gels directly contributes to rapid setting and high early strength development, with high-calcium precursors such as slag exhibiting faster strength gain than low-calcium systems, such as fly ash and metakaolin. Furthermore, the absence of vulnerable calcium hydroxide phases, combined with a densified, low-porosity aluminosilicate network, provides superior thermal stability, corrosion resistance, frost durability, and low permeability. Nevertheless, pronounced autogenous shrinkage and drying shrinkage, driven by mesopore moisture loss and the highly viscoelastic solid skeleton, remain primary constraints for field implementation. In grouting reinforcement, AAP can effectively enhance the strength and structural integrity of weak soils, such as soft clay, loess, and sulfate-rich saline soils. For grouting water-blocking, particularly in sodium-silicate-based binary systems, AAP achieves rapid gelation, superior washout resistance, and high anti-seepage pressure, proving optimal for groundwater inflow control. Future research must prioritize (i) standardized mix design protocols for performance consistency, (ii) advanced shrinkage mitigation strategies, (iii) systematic durability assessment under coupled environmental stressors (e.g., wet–dry cycling, chemical attack, thermal fatigue), and (iv) cross-disciplinary collaboration for industrial-scale validation. Full article

To promote the resource utilization of oilfield solid waste and facilitate the green and low-carbon transformation of transportation infrastructure, this study employed drilling cuttings from the Maye area of the Xinjiang oilfield and coal-fired furnace ash as primary raw materials. NaOH, Na₂O·nSiO₂, and Ca(OH)₂ were used as alkali activators to prepare alkali-activated solidification materials for oilfield road base applications. The optimal curing system identified in this study (4 wt.% NaOH + 20 wt.% furnace ash) falls within the commonly reported dosage ranges for alkali-activated solid-waste materials, where NaOH contents are typically 3%–8% and furnace ash contents 15%–30%. Considering the distinct chemical characteristics of the Xinjiang oilfield solid wastes, a targeted optimization strategy was adopted to achieve a balance between mechanical performance and economic feasibility. Based on mix-proportion experiments, macroscopic mechanical properties were evaluated. In combination with X-ray diffraction (XRD), laser particle size analysis, simultaneous thermal analysis (TG–DSC), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS), the influence of activator type on both mechanical performance and microstructural evolution was systematically investigated. The results indicate that the system containing 4 wt.% NaOH + 20 wt.% furnace ash exhibits the best overall performance, achieving a 28-day compressive strength of 4.81 MPa and a splitting tensile strength of 0.41 MPa, which are significantly higher than those of the Na₂O·nSiO₂ system (3 wt.% Na₂O·nSiO₂ + 20 wt.% furnace ash) and the Ca(OH)₂ system (4 wt.% Ca(OH)₂ + 15 wt.% furnace ash). The primary hydration products were identified as C-(N)-A-S-H and C-S-H gels. The type of alkali activator plays a decisive role in regulating hydration reaction kinetics and the spatial distribution of Ca and Si elements, thereby governing the hierarchical differences in macroscopic mechanical properties. In particular, NaOH generates a highly alkaline environment that promotes the dissolution of active Si/Al components in both drilling cuttings and furnace ash, enhances gel polymerization, and results in a denser microstructure. This study provides theoretical and technical support for the high-value utilization of oilfield solid wastes in highway base engineering. Full article

Magnesium phosphate cement (MPC) is widely used in rapid repair applications due to its fast setting, high early strength, and high-temperature resistance. However, the high cost of magnesium oxide (MgO) and the rapid hydration reaction make it challenging to control the setting time. In this study, steel slag powder (SSP) and ground granulated blast furnace slag (GGBS) were incorporated to partially replace MgO. The reactivity of SSP and GGBS was enhanced by an alkaline activator, promoting the dissolution of their glassy phases, which facilitated the formation of C-(A)-S-H gels and improved the performance of MPC. Experimental methods, including compressive strength testing, water resistance measurements, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), mercury intrusion porosimetry (MIP), and thermogravimetric analysis (TG), were used to evaluate the 28-day compressive strength and the microstructural characteristics of the modified MPC. When both SSP and GGBS were incorporated at 10 wt.%, the modified MPC achieved a 7-day compressive strength of 37.2 MPa, with the 28-day strength increasing to 50.2 MPa. The addition of an alkali activator with a modulus of 1.3 significantly boosted the 28-day strength to 62.3 MPa, while maintaining high flowability (215 mm). Microscopic characterization revealed that C₂S and C₃S in SSP undergo continuous hydration under alkaline conditions, while reactive silica-aluminum in GGBS reacted with phosphate to form a water-resistant C-(A)-S-H gel phase, optimizing the pore structure of MPC. This study provides a novel approach to developing low-cost, high-durability modified MPC with improved performance. Full article

This study presents the electrochemical characterization of a novel, binder-free, plasma-treated aluminum/carbon electrode (“Surge”) using lithium metal half-cells. The low operating potential near 0 V vs. Li/Li⁺ enables the investigation of the electrode’s charge storage mechanisms and stability limits. We compare its electrochemical behavior in coin cells (CR2032) against two reference configurations: (i) the Surge electrode with a thin copper backer (Surge + Cu-backer) and (ii) a commercial graphite electrode on an aluminum current collector (C-REF). The Surge electrode demonstrated ultra-high initial specific capacities of up to approximately 4500 mAh/g (cycle 1) with Coulombic efficiencies exceeding 85% after the formation cycle. The observed capacity significantly exceeds the theoretical value for Li-Al alloying (993 mAh/g), indicating that lithium plating within the porous carbon scaffold contributes substantially to the total charge storage. However, this high performance was limited to approximately 8 to 9 stable cycles. Post-cycling analysis via scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM/EDX) revealed a dominant failure mechanism: partial dissolution and consumption of the Al current collector leading to material redistribution. Quantitative EDX analysis showed a decrease in Al content from 45 at.% to 12 at.% alongside an increase in oxygen content from 8 at.% to 38 at.%, suggesting extensive Al-oxide formation. Critically, in the absence of a backer, Al-containing material deposited onto the stainless-steel cell components. The Cu backer served to redirect these deposits, improving current collection and modestly extending the short-term durability to approximately 1800 mAh/g at cycle 14 (approximately 75% capacity retention). In contrast, the C-REF control cell reached only approximately 1000 mAh/g (cycle 4) before failing within 5 to 6 cycles, underscoring the inherent instability of bare Al at low potentials. This characterization study establishes the Surge architecture as a successful proof-of-concept for ultra-high capacity charge storage and identifies Al dissolution as the dominant degradation mechanism. Future optimization must focus on stabilizing the Al substrate through protective interphases, alloying, or electrolyte engineering. Full article