Search Results (912)

The valorisation of significant quantities of wood biomass ash (WBA) in the production of building and construction materials is a sustainable approach to waste management. Due to their low chemical reactivity, the challenge for WBA-based alkali-activated materials (AAM) is improving their mechanical properties. To address this issue, WBA, containing wood biomass bottom ash and wood biomass fly ash, was used as the primary precursor. One aluminosilicate-rich material (coal fly ash (CFA), metakaolin (MK), or natural zeolite (NZ)) was added as a binary precursor at 10, 20, 30, and 40% of the total precursor mass (the mass of WBA plus the binary precursor) to compare its effectiveness. In the overall composition, the proportion of these aluminosilicate precursors was only 3.3–13.3%. Alkali activators consisted of 10% calcium hydroxide, 7 mol/L sodium hydroxide, and sodium silicate with the same solute mass as sodium hydroxide. Compressive strength and microstructural examinations (SEM-EDS, TG-DTA, XRD, XRF, and FTIR) were conducted on the produced AAM to analyse the mechanical performance and reaction mechanisms. A cradle-to-gate lifecycle assessment (LCA) was performed to evaluate the environmental impacts, including greenhouse gas emissions and energy consumption. The results show that NZ increased compressive strength by up to 57.62% when used at 6.6% in the composition. At the same time, MK and CFA increased strength by 33.05% and 47.15%, respectively. Binary precursors increased the greenhouse gas emissions and energy demands of AAM products, especially the MK, due to its energy-intensive calcination process. From a comprehensive view, NZ is the most efficient choice based on both mechanical and environmental insights. Full article

The accumulation of copper smelting slags generated by non-ferrous metallurgy represents both an environmental challenge and a potential source of technogenic raw materials for value-added products. In this study, the feasibility of producing magnesia–quartz proppants from secondary copper smelting slag formed after the pyrometallurgical extraction of iron and zinc was investigated. The slag, primarily composed of oxides of the SiO₂–CaO–Al₂O₃–MgO system, was processed by centrifugal melt granulation to obtain spherical granules suitable for proppant applications. The initial granules exhibited an amorphous glassy structure and insufficient mechanical strength, with up to 70% of particles destroyed under a pressure of 34.5 MPa. Controlled heat treatment within the temperature range of 300–1000 °C induced crystallization of silicate and aluminosilicate phases, leading to a significant improvement in mechanical performance. Optimal properties were achieved after holding at 800 °C for 60 min, where the fraction of crushed granules decreased to 10%, meeting the requirements of GOST R 54571-2011. The influence of MgO content on microstructure and strength was also examined. Increasing the MgO concentration from 5 to 16 wt.% resulted in grain refinement and improved crushing resistance, reducing the fraction of destroyed granules to 3%. To enhance chemical durability, a phenol–formaldehyde protective coating was applied, decreasing proppant solubility in a hydrochloric–hydrofluoric acid mixture from 19% to 2%. These results demonstrate that secondary copper smelting slag can serve as a promising raw material for producing standard-compliant proppants while contributing to the efficient utilization of metallurgical waste. 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

In recent years, phosphorus (P) nanoparticles have emerged as promising alternatives to conventional fertilizers. This study evaluated zeolite-fixed hydroxyapatite nanoparticles (nHAP) for greenhouse tomato cultivation, comparing their efficiency with phosphate rock (positive P input) and quartz sand (negative P Carrier). Material characterization by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and zeta potential analysis revealed that zeolite was identified predominantly as clinoptilolite, phosphate rock as phosphate-bearing aluminosilicates, and quartz sand as crystalline quartz; in all cases, the materials exhibited negatively charged surfaces. Hybrid fertilizers were formed through electrostatic interactions between zeolite and nHAP, confirming the successful development of a zeolite-based carrier for nanohydroxyapatite delivery. Application of 0.01 g·L⁻¹ nHAP increased the effective quantum yield of Photosystem II by 0.64 compared to the control at midday. Fruit firmness showed no significant differences among treatments. The highest sugar and soluble solids content was observed with 0.1 g·L⁻¹ nHAP (6.84 °Brix), whereas the 1 g·L⁻¹ treatment enhanced pigment concentrations, reaching 5.9 mg·g⁻¹/g chlorophyll a, 2.92 mg·g⁻¹ chlorophyll b, and 2.82 mg·g⁻¹ carotenoids. The 0.01 g·L⁻¹ dose of nHAP maintained quality characteristics and marginally increased yield; however, yield decreased at higher nHAP concentrations, opening new research opportunities to optimize this nanofertilizer. Full article

The limited high-temperature resistance of Ordinary Portland Cement (OPC) remains a critical challenge for fire-exposed and industrial concrete structures. Its performance deterioration above 500 °C is associated with dehydration and recrystallization of hydration products, leading to structural degradation of the cement matrix. To address this limitation, partial clinker replacement with fly ash combined with sodium water glass activation was proposed to enhance thermal stability. Physico-chemical analysis revealed the absence of portlandite and the formation of C-A-S-H and zeolite-like N–C–A–S–H phases in the fly ash-containing alkali-activated Portland cement. Upon heating, C-A-S-H phases sintered into stable high-temperature calcium aluminosilicate phases and zeolite-like phases underwent topotactic recrystallization into feldspathoid-type structures, preserving matrix integrity at high temperatures. The optimized composition region of cement system (fly ash—12.0–16.5 wt. %, density of water glass—1220–1240 kg/m³) was characterized by residual strength ≥ 50%, while compressive strength at 28 days was ≥80 MPa, exceeding the residual performance typically reported for conventional OPC systems under similar conditions (5–35%). The study was devoted to revealing the potential of low-emission Portland cements in high-temperature-resistant concretes through the utilization of fly ash. The mechanism that controls the compressive strength and temperature resistance of such cements has been demonstrated. Full article

This study investigates the feasibility of using calcined pumice as a sustainable precursor for geopolymer production. Natural pumice was calcined at different temperatures (600, 750, and 900 °C) and durations (1, 2, and 4 h). The effects of calcination were evaluated through color change, particle size distribution, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The results showed that calcination induced structural and mineralogical modifications in pumice, including increased disorder in the aluminosilicate network and partial recrystallization, which enhanced its reactivity. Consequently, geopolymer mortars produced with calcined pumice exhibited significantly improved compressive strength, with the highest strength of 53.5 MPa obtained for the sample calcined at 750 °C for 1 h, corresponding to an 84.5% increase compared to the mortar produced with raw pumice. In addition, calcination at 600 °C and 900 °C significantly improved water resistance. Considering mechanical performance, durability-related properties, and energy efficiency together, the calcination condition of 600 °C for 2 h was identified as the optimum treatment. These findings demonstrate that calcined pumice is a promising and sustainable precursor for geopolymer production. Full article

Geopolymer coatings exhibit outstanding corrosion resistance, high-temperature performance and thermal insulation. This thus holds broad application prospects in anti-corrosion of metals, protection of building structures, and functional coatings. However, the large-scale application of geopolymers is constrained by the availability of precursor materials. In South China, construction waste soil is predominantly composed of weathered residual soil of granite (WRSG), which is rich in silicate and aluminosilicate minerals. This soil can serve as a precursor for geopolymer synthesis upon activation. In this study, geopolymers were prepared using activated WRSG as the precursor material. The mix proportion of the geopolymers was optimized through single-factor experiments. Additionally, the hydration process and products of the geopolymer were characterized. The experimental results show that both high alkali content and low water-to-soil ratio contribute to achieving high compressive strength. The geopolymer has early strength characteristics. Its one-day compressive strength can reach 48% of 28-day value. The hydration products of the geopolymer mainly consist of amorphous sodium–aluminum–silicate–hydrate gel and primary minerals such as quartz and albite. With the increasing age, the content of chemically combined water and gel clusters grows, which densifies the microstructure and elevates the degree of hydration reaction of geopolymers. 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

Analyzing the hydrochemical characteristics and formation mechanism of metasilicic acid (H₂SiO₃) enrichment in the groundwater of Sanjiang Plain is conducive to guiding the rational development and utilization of mineral water resources in this region. Taking the groundwater in the typical black soil area of the northeastern Sanjiang Plain (from Qindeli Farm to Chuangye Farm) as an example, 104 groups of groundwater samples were collected to analyze enrichment and controlling factors of H₂SiO₃ by comprehensive methods such as hydrochemical analysis, rock geochemistry, water–rock interaction analysis, and ion ratio analysis. The results showed that the groundwater was generally in a reducing environment with low mineralization and weak acidity. The main cations were Ca²⁺ and Mg²⁺, and the main anion was HCO₃⁻. The hydrochemical types were mainly HCO₃–Ca and HCO₃–Ca·Mg, followed by HCO₃·Cl–Ca·Mg mixed type, and the H₂SiO₃ enrichment rate of groundwater reached 80.77%. The enrichment of H₂SiO₃ in the groundwater was related to the local geological structure and specific hydrogeochemical processes, and mainly controlled by the hydrolysis process of silicate rock minerals (such as albite, plagioclase, and olivine). The silicates and aluminosilicates contained in the basalt, diorite, and gneiss distributed in the area provided a rich material basis for the enrichment of H₂SiO₃. Its migration and distribution were simultaneously affected by leaching and cation exchange, while NO₃⁻ and SO₄²⁻ input from anthropogenic sources also participated in the rock weathering, specifically the enrichment process of H₂SiO₃ in the groundwater. From the perspective of mineralization conditions, Qinglongshan Farm and Qindeli Farm are potential areas for developing H₂SiO₃-rich mineral water. However, the main direction for the development and utilization of groundwater in this area should be to explore natural H₂SiO₃-rich groundwater with good comprehensive water quality. Full article

The construction sector is currently tasked with the critical challenge of minimizing CO₂ emissions associated with cement manufacturing. To support a sustainable building environment, this research developed cement-free alkali-activated composites by leveraging industrial by-products, specifically fly ash and blast furnace slag. The study experimentally evaluated how aluminosilicate material-based capsules (AMCs) composed of a mixture of fly ash, blast furnace slag, and ferronickel slag powder affect the composites’ durability, mechanical properties, and self-healing capabilities, alongside microstructural investigations. Results indicated that specimens incorporating 10% AMC reached a compressive-strength recovery range of 112–118%, which represents an improvement of approximately 10% compared to the control sample. Furthermore, the 28-day resistance to chloride ion penetration was enhanced by 79.4%, successfully meeting the ‘very low’ permeability criteria defined by ASTM C 1202. These results suggest that cement-free self-healing composites incorporating AMCs are a viable alternative for reducing carbon emissions and minimizing environmental impact in the construction industry. Furthermore, the recycling of industrial byproducts, as demonstrated herein, contributes to sustainable development in response to climate change. Full article

Red mud, a major solid waste from the alumina industry, suffers from an extremely low utilization rate due to its high alkalinity, complex chemistry, and particularly low cementitious activity, which drives the need for novel activation strategies. This study presents a new method for red mud activation through electrochemical treatment, which simultaneously enables iron recovery as a valuable by-product. The electrochemical activation was systematically investigated by performing experiments in alkaline, neutral, and acidic electrolytes. The alkaline system showed a pronounced enhancing effect on the electrochemical process. Under alkaline conditions, the average Faradaic efficiency exceeded 80%. The electrochemical treatment modified the microstructure of red mud particles and transformed iron oxides into magnetic species, which could be effectively separated via magnetic separation. More importantly, this activation process significantly enhanced the cementitious activity of the treated red mud by removing iron oxide that encapsulates reactive aluminosilicate phases and increasing surface reactivity. When used as a supplementary cementitious material with ordinary Portland cement and gypsum, the electrochemically activated red mud demonstrated remarkably improved mechanical properties, with 28-day compressive strength reaching up to 69 MPa. Characterization analysis revealed that the electrochemical activation promoted the formation of key hydration products, including C-S-H gel (formed through both OPC hydration and pozzolanic reactions between activated red mud and portlandite), ettringite, and portlandite. This work provides a green and low-carbon pathway for the stepwise utilization of red mud through activation and resource recovery. Full article

Geopolymers, a class of alkali-activated aluminosilicate binders, have emerged as a sustainable alternative for expansive soil stabilization. In this study, the swelling behavior of geopolymer-treated bentonite was systematically investigated using a Taguchi orthogonal design, complemented by XRD, FTIR, and SEM analyses to elucidate the underlying mechanisms. Specimens were compacted to an initial void ratio of e = 1.1, sealed, and cured under controlled conditions (22 ± 2 °C and 70 ± 2% relative humidity) prior to testing. The free swell ratio (FSR) was determined using a standardized free swelling test in accordance with GB/T 50123-2019, which is technically consistent with ISO 17892-13, under zero vertical surcharge. Each orthogonal condition was tested using a single specimen, and the reported values represent individual measurements. The results show that NaOH concentration is the dominant factor controlling swelling response, with a quantified contribution of 55.04%. The swelling behavior exhibits a distinct two-stage trend, characterized by an initial enhancement at low alkali concentrations followed by a significant suppression beyond a critical threshold of approximately 3 mol/dm³. Microstructural analyses reveal that this transition is governed by a progressive interlayer cation exchange, the structural dissolution of clay minerals, and the formation of geopolymer gel, which densifies the soil matrix and restricts interlayer expansion. These findings provide quantitative and mechanistic insight into the role of alkali activation in expansive clay stabilization and establish a practical concentration threshold for optimizing swelling suppression. Full article

The present study evaluates the electrochemical behaviour of reinforcing steel embedded in an alkali-activated eco-cellular geopolymer concrete designed for applications in environments with high chloride exposure. The material was formulated using a ternary precursor composed of fluid catalytic cracking residue (FCC), Class F fly ash, and ground granulated blast furnace slag (BFS), activated with an alkaline solution and combined with preformed foam to generate a microstructure characterised by predominantly closed porosity and low capillary connectivity. The electrochemical response of the system was assessed through open circuit potential (OCP) measurements, Tafel polarisation curves, electrochemical impedance spectroscopy (EIS), and potentiodynamic tests under accelerated exposure to NaCl solutions. The results demonstrate a markedly improved electrochemical performance, evidenced by shifts in OCP towards more noble values, reductions of 45–65% in corrosion current density (Icorr), and increases of up to fourfold in charge transfer resistance (Rct), together with the development of broader and more stable passive regions. This behaviour is attributed to the synergistic interaction between the formation of dense N-(C)-A-S-H (sodium/calcium–aluminosilicate hydrate) and C-(A)-S-H (calcium–aluminosilicate hydrate) gels, the eco-cellular architecture with low capillary connectivity, and the stable high alkalinity of the activated matrix, which collectively restrict ionic transport and promote the passive stability of the reinforcing steel—defined here by noble OCP values, low Icorr, high Rct, and sustained passive domains in polarisation curves. Overall, the findings position the developed eco-cellular geopolymer concrete as a sustainable, high-performance alternative for infrastructure exposed to chloride-rich environments. Full article

The growing accumulation of coal beneficiation waste represents a significant environmental and technological challenge while simultaneously creating opportunities for the resource recovery within circular economy frameworks. This study presents the development and process-oriented evaluation of an environmentally safe technology for converting coal beneficiation waste into potassium humate, with the simultaneous recovery of molybdenum compounds via alkaline extraction. The proposed solution is designed to improve resource efficiency, reduce the volume of waste directed to landfilling, and generate a high value-added product for agricultural and technological applications. The process flow includes preliminary characterization and preparation of the waste, determination of moisture, ash, and organic matter content, and the separation of metal-bearing fractions. Alkaline extraction was carried out using potassium hydroxide under controlled temperature and reaction time conditions, followed by purification and concentration of the humate solution. The process management strategy focuses on optimizing key technological parameters, including alkali concentration, solid-to-liquid ratio, temperature, and reaction time, to maximize humate yield while preserving functional groups responsible for biological activity. Comprehensive physicochemical, thermal, and mineralogical analyses confirmed the stability of the aluminosilicate matrix and the suitability of the material for alkaline processing without adverse structural degradation. Biological tests using oat (Avena sativa) demonstrated that potassium humate derived from coal beneficiation waste exhibits higher growth-stimulating effectiveness than a conventional commercial humate. Economic analysis revealed a strong correlation between humic acid content and added value, confirming the feasibility of transforming coal beneficiation waste from an environmental burden into a valuable secondary resource. Full article

Mullite (Al₆Si₂O₁₃), an aluminosilicate with remarkable thermal and dielectric properties, is a promising material for advanced electronic applications. This study focuses on a sintered mullite composite and examines its structural, morphological, dielectric, and electrical properties. X-ray diffraction and scanning electron microscopy analyses confirm a well-defined crystalline structure and a homogeneous microstructure. Impedance spectroscopy measurements reveal a high relative permittivity at low frequencies, dominated by interfacial and jump polarization mechanisms. Electrical conductivity follows Jonscher’s double-power law, reflecting mixed ionic and electronic conduction due to contributions from grains and grain boundaries. Analysis of the Nyquist diagrams shows a marked decrease in resistances with increasing temperature: The grain resistance decreases from 21.87 MΩ to 4.85 MΩ, while that of the grain boundaries decreases from 89.44 MΩ to 5.94 MΩ between 450 °C and 900 °C. In addition, the relative permittivity increases sharply with temperature, from 25 × 10³ to 350 × 10³ at 1 kHz and from 200 to 1 × 10³ at 1 MHz over the same temperature range, highlighting the dominant influence of temperature and low frequencies on polarization mechanisms. These results confirm the strong potential of sintered mullite for electronic applications. The activation energy of the grain and grain boundary were determined to be E_a,g = 0.18 eV and E_a,bg = 0.22 eV, respectively. Full article