Search Results (206)

The utilization of recycled concrete aggregate presents an effective solution for construction waste mitigation. However, concrete service in sulfate environments leads to sulfate ion retention in recycled aggregates, substantially impairing their quality and requiring modification approaches. A critical question remains whether traditional recycled aggregate modification techniques can effectively enhance the performance of these sulfate-containing recycled aggregates (SRA). Cement paste wrapping in various proportions was used in this investigation to enhance SRA. The performance of both SRA and modified aggregates was systematically assessed through measurements of apparent density, water absorption, crushing value, and microhardness. Microstructural analysis of the cement wrapping modification mechanism was conducted by scanning electron microscopy coupled with mercury intrusion porosimetry. Results revealed that internal sulfate addition decreased the crushing value and increased the water absorption of recycled aggregates, primarily due to micro-cracks formed by expansion. Additionally, the pores were occupied by erosion products, leading to a slight increase in the apparent density of aggregates. The performance of SRA was effectively enhanced by cement paste wrapping at a 0.6 water–binder ratio, whereas it was negatively impacted by a ratio of 1.0. The modifying effect became even more effective when 15% fly ash was added to the wrapping paste. Scanning electron microscopy observations revealed that the interface of SRA was predominantly composed of gypsum crystals. Cement paste wrapping greatly enhanced the original interface structure, despite a new dense interface formed in the modified aggregates. Full article

The aim of this study was to improve the efficiency of in situ uranium leaching by developing a specialized methodology for selecting rational parameters for the chemical treatment of production wells. This approach was designed to enhance the filtration properties of ores and extend the uninterrupted operation period of wells, considering the clay content of the productive horizon, the geological characteristics of the ore-bearing layer, and the composition of precipitation-forming materials. The mineralogical characteristics of ore and precipitate samples formed during the in situ leaching of uranium under various mining and geological conditions at a uranium deposit in the Syrdarya depression were identified using an X-ray diffraction analysis. It was established that ores of the Santonian stage are relatively homogeneous and consist mainly of quartz. During well operation, the precipitates formed are predominantly gypsum, which has little impact on the filtration properties of the ore. Ores of the Maastrichtian stage are less homogeneous and mainly composed of quartz and smectite, with minor amounts of potassium feldspar and kaolinite. The leaching of these ores results in the formation of gypsum with quartz impurities, which gradually reduces the filtration properties of the ore. Ores of the Campanian stage are heterogeneous, consisting mainly of quartz with varying proportions of clay minerals and gypsum. The leaching of these ores generates a variety of precipitates that significantly reduce the filtration properties of the productive horizon. Effective compositions and concentrations of decolmatant (clog removal) solutions were selected under laboratory conditions using a specially developed methodology and a TESCAN MIRA scanning electron microscope. Based on a scanning electron microscope analysis of the samples, the effectiveness of a decolmatizing solution based on hydrochloric and hydrofluoric acids (taking into account the concentration of the acids in the solution) was established for the destruction of precipitate formation during the in situ leaching of uranium. Geological blocks were ranked by their clay content to select rational parameters of decolmatant solutions for the efficient enhancement of ore filtration properties and the prevention of precipitation formation. Pilot-scale testing of the selected decolmatant parameters under various mining and geological conditions allowed the optimal chemical treatment parameters to be determined based on the clay content and the composition of precipitates in the productive horizon. An analysis of pilot well trials using the new approach showed an increase in the uninterrupted operational period of wells by 30%–40% under average mineral acid concentrations and by 25%–45% under maximum concentrations with surfactant additives in complex geological settings. As a result, an effective methodology for ranking geological blocks based on their ore clay content and precipitate composition was developed to determine the rational parameters of decolmatant solutions, enabling a maximized filtration performance and an extended well service life. This makes it possible to reduce the operating costs of extraction, control the geotechnological parameters of uranium well mining, and improve the efficiency of the in situ leaching of uranium under complex mining and geological conditions. Additionally, the approach increases the environmental and operational safety during uranium ore leaching intensification. Full article

Phosphogypsum, a by-product of phosphate fertilizer production, was predominantly used as a supplementary additive in recycled construction materials. However, there are few detailed studies on utilizing phosphogypsum as the primary component in inorganic cementing materials while achieving cost-effective detoxification. This study aimed to develop a harmless phosphogypsum-based inorganic cementing material (PICM) mainly based on phosphogypsum, in which cement, quicklime, and a stabilizer were used as additives. Harmful ions and acidity were first detected through X-ray fluorescence and ion chromatography and then harmlessly treated with quicklime. Compaction parameters, mechanical performance, X-ray diffraction analysis, moisture, and freezing resistance were characterized successively. The results illustrated that fluoride and phosphate ions were the primary soluble contaminants, whose leaching solution concentration can be reduced to 15.31 mg/L and undetectable with 2% quicklime through the mass proportion of phosphogypsum added and mixed. Meanwhile, the corresponding pH value was also raised to over 8. Cement content and quicklime were positively correlated with PICM’s maximum dry density. PICM with 25% cement and 2.5% stabilizer presented the highest unconfined compression strength, and flexural strength did not show significant regularity. PICM was mainly composed of quartz, gypsum, ettringite, and calcite, whose content decreased as cement content and quicklime content increased. Stabilizer, quicklime and cement content were positively correlated with PICM’s freezing and moisture resistance. Full article

The aim of this study is to determine the characteristics of the chemical and mineral composition of sediment layers in a technogenic settling pond. This pond is located on urban land in Berezniki (Perm Krai, Russia), outside the territory of operating industrial facilities, and contains alkaline saline industrial wastes. The origin of this waste was related to sludge from the Solvay soda production process, which had been deposited in this pond over a long period of time. However, along with the soda waste, the pond also received wastewater from other industries. As a result, the accumulated sediment is characterized by variation in morphological properties both in depth and laterally. Five undisturbed columns were taken to study the composition of the accumulated sediment. The obtained samples were analyzed by X-ray diffraction (XRD), synchronous thermal analysis (STA), and X-ray fluorescence (XRF) analysis. The results showed that the mineral composition of bottom sediments in each layer of all studied columns is characterized by the predominance of calcite precipitated from wastewater. Along with calcite, due to the presence of magnesium and sodium in the solution, other carbonates precipitated—dolomite and soda (natron), as well as complex transitional carbonate phases (northupite and trona). Together with carbonate minerals, the chloride salts halite and sylvin, sulfate minerals gypsum and bassanite, and pyrite and nugget sulfur were established. The group of terrigenous mineral components is represented by quartz, feldspars, and aluminosilicates. The chemical composition of sediments in the upper part of the section generally corresponds to the mineral composition. In the lower sediment layers, the role of amorphous phase and non-mineral compounds increased, which was determined by the results of thermal analysis. The content of heavy metals and metalloids also increases in the middle and lower sediment layers. When categorized according to the Igeo value, an excessive degree of contamination (class 6) was observed in all investigated columns for copper content (Igeo 5.2–6.1). Chromium content corresponds to class 5 (Igeo 4.1–4.6), antimony to class 4 (Igeo 3.0–4.0), and lead, arsenic, and vanadium to classes 2 and 3 (moderately polluted and highly polluted). The data obtained on variations in the mineral and chemical composition of sediments represent the initial information for the selection of methods of accumulated waste management. Full article

To investigate the influence of the water–cement ratio and erosion patterns on the deterioration of concrete in a sulfate corrosion environment, concrete specimens with different water–cement ratios were immersed in Na₂SO₄ solutions of varying concentrations (0%, 5%, and 8%). The immersion times were set at 0 days, 30 days, 60 days, and 90 days. Macro-scale compressive strength tests and micro-scale performance tests were conducted to obtain the damage morphology, micro-scale elastic modulus, and hardness of eroded concrete. Additionally, K-means clustering analysis was used to analyze the micro-mineral phases of the specimens, and SEM and XRD were employed to reveal the degradation mechanisms of sulfate erosion on the microstructure of concrete. The results indicated that the erosion products of calcium aluminate and gypsum in concrete gradually increased with the increase in Na₂SO₄ solution concentration and immersion time. In the early stages of erosion, the compressive strength and corrosion resistance coefficient of concrete showed a temporary upward trend, which then decreased as the erosion depth increased. From a microstructural perspective, erosion had a significant impact on the internal structure of concrete, while the elastic modulus and hardness of hydrated calcium silicate and calcium hydroxide under erosion showed relatively minor changes, both exhibiting a gradual decrease. The volume fraction of microporous pores gradually increased, further exacerbating the depth and extent of erosion. Full article

This study demonstrated the effectiveness of using autoclaved aerated concrete AAC waste as a low-cost filtering material for removing hydrogen sulfide (H₂S) from gas streams. A long-term experiment (89 days) was conducted in a packed bed reactor to purify synthetic biogas composed of N₂, CO₂, H₂S, and O₂. Optimal H₂S removal efficiencies, reaching up to 100%, were achieved under highly acidic conditions (pH ≈ 1–3) and low oxygen concentrations (<1%). In the presence of oxygen, calcium oxides in the AAC waste react with H₂S to form gypsum (CaSO₄ 2H₂O). The simultaneous removal of both oxygen and H₂S by AAC waste, following an approximate 2:1 molar ratio, may be particularly beneficial for biogas streams containing unwanted traces of oxygen. The transformation and lifespan of AAC waste were monitored through sulfur accumulation in the material and pressure drop measurements, which indicated structural changes in the AAC waste. At the end of its lifespan, the AAC waste exhibited an H₂S removal capacity of 185 g_H2S kg_AAC⁻¹. This innovative and sustainable process not only provides a cost-effective and environmentally sound solution for the simultaneous removal of H₂S and O₂ from biogas, but also promotes waste valorization and aligns with circular economy principles. Full article

Ultra-high-performance concrete (UHPC) is known for its outstanding strength and durability but is often limited by the high cost of traditional materials, like cement, fine aggregates, and silica fume. This review examines the use of industrial by-products—specifically, iron tailings, steel slag, and desulfurization gypsum—as sustainable alternatives in UHPC mix design. These materials serve as supplementary cementitious components and fine aggregates, helping reduce environmental impacts and production costs. This study highlights the synergistic hydration mechanisms between Portland cement and waste-based materials, leading to improved microstructure and long-term strength. The role of steel fibers in enhancing crack resistance is also discussed. Challenges related to workability, cost, and lack of standardization are addressed, along with opportunities for innovative mix designs, low-carbon binders, and 3D printing. Overall, this paper underscores the potential of industrial by-products to advance sustainable, high-performance UHPC solutions. Full article

Foamed geopolymer materials are increasingly studied due to their inherent fire resistance. To date, these materials have primarily been produced by casting into moulds, with foaming occurring during mixing or within the moulds, shortly before setting. For practical applications, however, it is advantageous to apply these materials directly onto surfaces with complex geometries. Although several techniques for geopolymer spraying have been described in the literature, many exhibit limitations that restrict their practical implementation. This study presents a novel spraying technology developed on a dedicated process line, enabling in situ dosing of the foaming agent immediately before application. The system integrates infrared heating to ensure controlled curing of the geopolymer. This paper outlines the design of the process line and its core functionalities while presenting selected results of material tests conducted on the obtained geopolymer coatings. Tests performed on approximately 200 m² of surface confirmed the functionality of the process. The thermal conductivity of the sprayed foams was about 0.07 W/m-K. The inclusion of a phase-change material (PCM) in the geopolymers further enhanced their ability to store and regulate thermal energy. The adhesion strength results, consistently exceeding 1 MPa across various substrates (steel, geopolymer, gypsum board), confirmed the practical suitability of the proposed solution. This was also demonstrated by the homogeneous foamed structure obtained. Full article

With the aim of reducing the environmental impact of buildings, the appropriate selection of building materials is essential, as a building is a complex system composed of various materials. With this background, a multi-criteria decision-making approach has recently gained traction. This study demonstrated the effect of building material selection on both environmental and economic parameters of a building in the context of Japan. A comparative analysis of five structural frame options was conducted utilizing a reference building model to assess the implication of material choices. The findings indicated that wooden frame options are advantageous in environmental aspects compared to non-wooden frames, provided that sustainable forestry practices and appropriate recycling scenarios are implemented. Conversely, it was found that a Cross Laminated Timber (CLT) frame is the most expensive option. This suggests that a hybrid approach, which combines various frame materials, could yield a more effective solution in terms of both environmental and economic sustainability. In addition, it was highlighted that building envelopes, such as foundation, exterior wall, and roof, should be prioritized to enhance the sustainability of a building from a material perspective. Furthermore, gypsum board, commonly used for sheathing building elements, should be selected with careful consideration of its environmental impact. Full article

In this study, a novel calcium phosphate/polyacrylamide copolymer/$\alpha$-type hemihydrate gypsum (CPO/PAM/$\alpha$-HHG) composite material was prepared by polymerising a stable inorganic CPO precursor, end-capped with triethylamine (TEA), with an organic polyacrylamide (PAM) hydrogel to form a CPO/PAM precursor solution. Subsequently, this precursor solution was mixed with inorganic $\alpha$-hemihydrate gypsum. The effects of CPO/PAM precursor addition and CPO addition on the slurry flowability, initial setting time, and mechanical properties of hardened specimens of the CPO/PAM/$\alpha$-HHG composite were investigated. The structural characteristics of the composites were analysed by XRD, FE-SEM, and TGA. The results show that the initial setting time of the CPO/PAM/$\alpha$-HHG composites was 26.7 min, which was 140.5% longer than that of the pure water $\alpha$-HHG system and 3.9% longer than that of the PAM/$\alpha$-HHG system; additionally, the oven-dried specimens had a flexural strength of 27.59 MPa and a compressive strength of 68.48 MPa, which were 77.2% and 102.0% higher than those of the pure water $\alpha$-HHG system and 38.8% and 14.1% higher than those of the PAM/$\alpha$-HHG system, respectively. The wet compressive strength of the CPO/PAM/$\alpha$-HHG composites was improved by 11.8% compared to that of the PAM/$\alpha$-HHG system. A structural analysis showed that CPO promoted the gelation process of PAM and allowed the hydration reaction process of $\alpha$-HHG to be fully carried out by slowing down the gelation process of the organic network, which led to the full development of both organic and inorganic networks, ultimately forming an interspersed inorganic/organic dual-network structure, which enhanced the comprehensive mechanical properties of the composites. This study provides a new idea for the modification of $\alpha$-type hemihydrate gypsum and a new method for the preparation of high-utilisation and high-performance gypsum-based composites. Full article

With the intensifying global energy crisis, ensuring robust and reliable energy reserves has become crucial, and underground energy storage offers a safe, large-scale, and cost-effective solution. Among various options, salt cavern gas storage is recognized for its excellent sealing capacity and geological stability; however, many natural salt domes contain inherent fissures and interlayers (e.g., gypsum) that can jeopardize operational safety. Hence, this study aims to clarify how different fissure angles and bedding plane dip angles affect the mechanical behavior of salt–gypsum composites, providing insights for enhancing safety measures in underground gas storage facilities. Based on practical engineering demands, we employ finite element software (RFPA2.0) under a confining pressure of 25 MPa to investigate the compressive strength, fractur patterns, and acoustic emission responses of salt–gypsum composites with varying bedding plane and fissure angles. The results indicate that (1) the composite’s compressive strength gradually increases with the fissure angle, being lowest at 0° and highest at 90°; (2) as the bedding plane angle increases, the compressive strength first rises, then decreases, and finally rises again, with its minimum at 60° and maximum at 90°; and (3) when the bedding plane angle exceeds 60°, cracks preferentially develop along the bedding plane, dominating the overall fracture process. These findings provide theoretical guidance for optimizing the design and ensuring the long-term safety and stability of underground salt cavern gas storage systems. Full article

The construction industry generates approximately 45% of the world’s total waste, highlighting the need for sustainable solutions. This study investigates the incorporation of quartzite waste (QW) and fiberglass waste (FW) into the production of gypsum plasterboard to reduce its environmental impact while maintaining its structural performance. The optimum formulation (MQ-20) was determined by replacing 20% of the gypsum with QW, based on the observed free water loss and crystallization water. The physical, mechanical, and thermal properties of the reference and modified boards were evaluated. The results showed that the MQ-20 samples exhibited a 30% reduction in flexural strength compared to the reference, while still exceeding regulatory standards. In addition, the MQ-20 samples had a lower thermal conductivity (0.54 W/(m∙K)) than the reference (0.58 W/(m∙K)). Fire-resistance tests showed that the inclusion of QW and FW reduced the size and number of cracks, improving the structural stability of the plasterboard at high temperatures. This research demonstrates that the incorporation of industrial waste into plasterboard is a viable and environmentally friendly approach, providing both mechanical and thermal performance benefits. These findings provide a basis for future studies aimed at developing sustainable building materials with improved functional properties. Full article

In western Jilin Province, China, the presence of soda saline–alkali soil poses a significant threat to the raising of rice seedlings due to its harsh soil properties. The scarcity of suitable seedling-raising soil resources has become increasingly pronounced. A short-term soil-improvement experiment was conducted using the original saline–alkali soil sourced from the rice-growing region of Jilin Province, followed by the rice-seedling-raising test in the improved soil to identify an effective soil-improvement strategy. Four distinct treatments were established: no amendment (JCK); gypsum and straw (JCW); gypsum, straw, and sulfuric acid (JCWH); and gypsum, straw, and chemical fertilizer (JCWF). The effects of these amendment treatments on the soil physicochemical properties (pH, electrical conductivity, exchangeable sodium, total alkalinity) were evaluated, as well as the effects on soil organic carbon (SOC) and its components including humic acid carbon (HAC), and fulvic acid carbon (FAC). The results indicated that, compared to the control group, all amendment treatments effectively reduced the average soil pH by 0.53 to 0.79 units and decreased exchangeable sodium by 56.7% to 74.8%. Furthermore, the average SOC, HAC, and FAC increased by 48.3%, 89.4%, and 56.0%, respectively. Among the treatments, JCWH proved to be the most effective. After two years of improvement, the rice seedlings in the JCWH-treated soil exhibited the highest dry weight and plant height, surpassing those grown in the farmer’s seedling-raising soil. The scheme of utilizing soda saline–alkali soil for rice-seedling raising, following a short-term improvement treatment with corn straw, gypsum, and sulfuric acid (JCWH), provides technical support and an effective solution to the soil scarcity issue faced by seedling farmers in saline–alkali regions. Full article

Fire has been proven to threaten human lives and buildings significantly. Extensive research is being conducted globally to reduce fire risks, particularly in high-rise buildings that incorporate steel for structural support, timber for decorative elements, and cladding for insulation. Traditional passive fireproofing materials, such as concrete coverings, gypsum boards, and cementitious coatings, often lack aesthetic appeal. Intumescent coatings offer a promising solution to this issue. These coatings require a thin layer on the substrate to protect from fire, and the thin layer expands up to many times its original thickness when exposed to fire, forming an insulating char that acts as a barrier between fire and the substrate. This barrier prevents the steel from reaching critical temperature and helps maintain its integrity during a fire incident. Hence, intumescent coatings are a great choice for passive fire protection of load-bearing steel, wooden structures, timber, and cementitious buildings. Although some research articles discuss intumescent coating types, application methods, fabrication processes, cost-effectiveness, bonding performance, toxicity, and various uses, a comprehensive study encompassing all these topics still needs to be conducted. This review paper explores different types of intumescent coatings, their formulation and manufacturing methods, their application processes, and their use on various substrates. It also covers the key intumescent coating materials and their interactions during fire. Challenges and issues, such as fire protection time, char-forming temperature, and toxicity, are discussed. Full article

Super sulfate cement (SSC) serves as a sustainable alternative to ordinary Portland cement, offering lower carbon emissions and superior performance. Magnesium oxide (MgO) and building gypsum (BG) were utilized as activators for granulated blast furnace slag (GBFS), and together they formed SSC, which was employed to stabilize the waste soft clay (SC). The mechanical strength development characteristics of solidified clay and the types of its hydration products were investigated through mechanical experiments, including unconfined compressive strength (UCS) tests as well as microscopic experiments, such as X-ray diffraction tests and scanning electron microscopy tests. The mass ratios of GBFS, MgO, and BG were 8:2:0 (A2) and 6:2:2 (B1), respectively; these ratios were employed to stabilize the clay, resulting in solidified clay samples designated as S-A2 and S-B1. The UCS of S-B1 increased by 36.5% to 49.3% compared to S-A2 at the curing time from 7 to 91 days. The strength residual coefficients were 34.5% and 39.1% for S-A2 and S-B1, respectively, after ten wet–dry cycles. After soaking in sodium sulfate solution, the UCS of S-A2 and S-B1 decreased by 49.1% and 29.8%, respectively, compared to the unsoaked condition. The results of microscopic tests showed that the hydration products of S-B1 mainly included needle-like calcium silicate hydrate (C-S-H) gel, flaky hydrothermal gel, and ettringite (AFt) crystals. BG promoted the formation of AFt, while MgO facilitated the generation of C-S-H gel. In this study, SSC was used to stabilize the waste clay, which provided a way for the application of waste SC and SSC. Full article