Search Results (750)

In the era of increasing generation of various waste streams, the possibility of utilizing them as secondary resources is of utmost importance and fully corresponds to the goals of the circular economy. Industrial residues from the pulp and paper industry, such as biomass combustion ash (FARP) and sludge from industrial wastewater treatment (PPWS), together with natural zeolite as a modifying additive, represent valuable sources enabling their integrated valorization. The present study aims to investigate the potential for their reuse through the development of sustainable material blends. A comprehensive analysis of the chemical composition and morphology of the obtained mixtures was carried out using inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate a tendency for the formation of mineral matrices dominated by calcium–sulfur–oxygen (Ca–S–O) phases, with the presence of calcium sulfate and aluminosilicate structures. The blends are associated with the formation of stable crystalline structures exhibiting potential pozzolanic activity. In this way, carbon is captured and fixed in a stable mineral form. The obtained results suggest the potential of these blends for use in low-carbon systems focused on waste valorization and carbon retention. The materials may be suitable for applications in construction, soil remediation, and environmental technologies, contributing to closing the resource loop “from farm to table and back again”. Full article

The Qianlong Stone Classics are the largest and best-preserved ensemble of officially commissioned stone inscriptions of Confucian classics extant, yet their stele bases are currently threatened by salt efflorescence. Fluctuations in ambient temperature and humidity contribute significantly to this deterioration. Taking Stele 17 as a representative case, this study assesses the risks of surface condensation and moisture-induced salt phase transitions through integrated temperature–humidity monitoring, infrared thermography, and soluble salt analysis. The risk of condensation remains low under typical conditions, as the stele base surface temperature exceeds the dew point by at least 0.5 °C. However, risks of salt deliquescence and hydration are substantial. The stone surface contains elevated levels of soluble salts, including four highly soluble species (sodium sulfate, calcium nitrate, sodium nitrate, and sodium chloride) and one moderately soluble species (calcium sulfate). Deliquescence phase transition humidities are approximately 50.5% for calcium nitrate, 74.3% for sodium nitrate, and 75.4% for sodium chloride, while sodium sulfate exhibits a hydration phase transition near 81%. Exhibition Hall humidity fluctuates around these critical thresholds, driving repeated dissolution–crystallization and hydration–dehydration cycles that progressively erode the stone microstructure. These hygrothermal cycles exhibit pronounced seasonal patterns, with frequent air-conditioning operation in summer amplifying thermal and humidity impacts. This study elucidates an air-moisture-driven salt deterioration mechanism distinct from classical capillary rise, clarifies the persistent progression of efflorescence in transitional seasons, and provides a scientific basis for optimizing environmental control strategies. Full article

Gypsum-based fire protection relies on thermally activated dehydration, where chemically bound water is released and evaporated, thereby providing an endothermic heat sink that delays heat penetration through assemblies. In parallel, inorganic hydrated salts are increasingly used as flame-retardant additives in gypsum-based systems to enhance heat absorption over specific temperature ranges. Fire simulation tools and performance-based fire engineering approaches require reliable kinetic data and reaction enthalpies that can be implemented as coupled thermal–chemical source terms. However, additive-specific kinetic datasets remain limited, particularly under restricted vapor exchange conditions representative of porous construction materials. This work investigates the thermal decomposition behavior and dehydration kinetics of Aluminum Trihydrate (Al(OH)₃, ATH), Magnesium Hydroxide (Mg(OH)₂, MDH), Calcium Aluminate Sulfate (3CaO·Al₂O₃·3CaSO₄·32H₂O, CAS), and Magnesium Sulfate Heptahydrate (MgSO₄·7H₂O, ESM) with emphasis on vapor-restricted conditions representative of confined porous systems. Differential scanning calorimetry (DSC) experiments were conducted at three heating rates (2, 10, and 20 K/min for MDH, CAS and ESM and 20, 40 and 60 K/min for GB-ATH) up to 600 °C using pinhole crucibles to simulate autogenous vapor pressure. The thermal analysis indicates that ATH and MDH exhibit predominantly single-step dehydration behavior, while ESM shows a complex multi-step mechanism. Although CAS presents a single dominant thermal peak in the DSC signal, the isoconversional analysis reveals a multi-stage reaction behavior, demonstrating that peak-based interpretation alone may be insufficient for such systems. Kinetic parameters were determined using both model-free (Starink) and model-fitting approaches in accordance with the recommendations of the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). All reactions were consistently described using the Avrami–Erofeev model as an effective phenomenological representation of the conversion behavior. The extracted kinetic triplets were validated through numerical simulations, showing good agreement with experimental conversion and reaction rate data. The resulting kinetic parameters and dehydration enthalpies provide a physically consistent dataset for the description of dehydration processes under restricted vapor exchange. These results support the development of thermochemical models for gypsum-based systems; however, their transferability to full-scale assemblies remains subject to validation under coupled heat- and mass-transfer conditions. Full article

Local antibiotic delivery has gained a central role as an adjunct to radical debridement in chronic osteomyelitis, allowing high antimicrobial concentrations at the infection site while reducing systemic toxicity. This narrative review summarizes the current clinical evidence on commercially available antibiotic-loadable bone substitutes, with particular focus on calcium sulfate (CaSO₄)-based systems and biphasic calcium sulfate/hydroxyapatite (CaS/HA) composites. Nineteen studies were included. Differences in formulation, resorption kinetics, antibiotic elution profile and osteoconductive behavior are discussed, alongside clinical outcomes including recurrence of infection, reoperation rates and complication patterns. Finally, based on the currently available evidence and expert recommendations, practical guidance is proposed to support carrier selection in different clinical scenarios (cavitary vs. corticomedullary defects; high-risk soft tissue; polymicrobial or resistant infections). Across published series, although heterogeneous, infection eradication rates are generally high when local carriers are integrated into structured surgical protocols. Calcium sulfate carriers provide rapid resorption and robust early antibiotic release but are associated with higher rates of sterile wound drainage. In contrast, CaS/HA biocomposites demonstrate more gradual remodeling and radiographic integration, potentially improving defect consolidation and reducing wound-related morbidity, although leakage and cost considerations remain relevant. Full article

Coal-fired power plants can adversely affect aquatic ecosystems through wastewater discharge, waste landfills, and the atmospheric deposition of toxic substances released during coal combustion. These processes degrade the water quality of nearby surface and underground water bodies. The study presents the impact of the coal-fired power plant Contour Global Maritza East 3 on the ecological status of the Sokolitsa River, reflected by changes in the composition and structure of the sensitive phytobenthos and macrozoobenthos communities and supporting environmental variables, including water temperature, pH, dissolved oxygen, conductivity, nutrients, sulfates, calcium, and calcium carbonate hardness. Methods for monitoring and assessing the ecological status of surface water bodies compliant with European and national legislation were applied to the studied biological quality elements and key physicochemical variables. Historical monitoring data from a ten-year period, 2013–2022, together with data collected during the study in 2023 and 2024 were analyzed and evaluated. The results indicated a significant increase in most physicochemical variables downstream of the CFPP compared with the upstream site, including water temperature, conductivity, calcium carbonate hardness, calcium, sulfates and nitrogen (N) nutrients (ammonium N, nitrite N, nitrate N, total N). The ecological status of the river deteriorated, as indicated by the negatively affected aquatic habitats and the changes in the taxonomic richness and abundance of the studied organism groups. Full article

Precise water quality forecasting is vital for sustainable resource management and public health, especially in semi-arid environments. This study investigates the predictive capabilities of ten Machine Learning (ML) algorithms using a dataset of 308 drinking water samples collected from various districts in Şanlıurfa Province, Türkiye. We evaluated ten predictive models, including Support Vector Regressor (SVR) and Extreme Gradient Boosting (XGBoost), both integrated with dimensionality reduction and hyperparameter optimization. Nineteen physicochemical and microbiological parameters—Temperature, chlorine (Cl⁻), pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), nitrite (NO₂⁻), nitrate (NO₃⁻), ammonium (NH₄⁺), sulfate (SO₄²⁻), Free Chlorine (Cl₂), calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), potassium (K⁺), fluoride (F⁻), trihalomethanes (THMs), Escherichia coli, Enterococci, Total Coliform—were used as input features. The dataset was split into training (75%) and testing (25%) subsets, and model performance was assessed through 10-fold cross-validation and hold-out testing procedures. To improve model generalization and mitigate the effects of class imbalance, we implemented the Adaptive Synthetic Sampling (ADASYN) technique. ML algorithms were evaluated using standard regression metrics: Mean Absolute Error (MAE), Mean Squared Error (MSE), Root Mean Squared Error (RMSE), and the Coefficient of Determination (R²). The LSTM model optimized using Randomized Search outperformed the SVR and XGBoost models, demonstrating the highest accuracy and generalization capability, as evidenced by the superior R² value of 0.999 following ADASYN balancing and the lowest RMSE (1.206). These findings underscore the effectiveness of the LSTM framework in modeling the complex variance of the Weighted Arithmetic Water Quality Index (WAWQI). The findings of this study are expected to support future water quality monitoring strategies, inform policy development, and contribute to sustainable water resource management in arid and semi-arid regions. Full article

To upgrade the mechanical properties and reduce the high brittleness of coral aggregate concrete (CAC), calcium sulfate whisker (CSW) has been innovatively used as a reinforcing material in this study. Five incorporation levels (0–4%) were designed to systematically investigate the evolution mechanism of CAC mechanical, microstructure, and pore characteristics at different curing ages. The results showed that CSW incorporation can significantly improve the mechanical properties of CAC; 1% CSW can bring 36.7% enhancement to 14-day compressive strength, and 11.9% improvement to 28-day splitting tensile strength with 2% CSW. Mechanism analysis revealed that appropriate CSW content effectively suppressed microcrack propagation through whisker bridging effects and remarkably enhanced the cement paste–coral aggregate interfacial bond strength by 71%, promoting a transition in failure mode from interfacial failure to aggregate fracture. At the same time, CSW improved the pore structure by reducing the proportion of macropores and increasing the micropore proportion to 76% with 1% CSW content. However, the performance deterioration of CAC caused by CSW excess (4%) was mainly due to the defect formation resulting from whisker agglomeration. The proposed strength prediction models (R² > 0.93) based on experimental data can reliably describe the enhancement effect of CSW. Full article

The buildings and construction sector is a major contributor to global environmental impact, accounting for 34% of global energy demand and 37% of energy- and process-related CO₂ emissions in 2022. This context motivates the development of alternative construction materials with lower embodied energy and reduced environmental impact. In this study, vibrocompressed calcium sulfate prefabricated elements were developed and experimentally evaluated as an alternative to conventional concrete-based units. Unlike traditional gypsum molding processes, the proposed vibrocompression route enables the production of semi-dry mixtures with reduced water content, allowing rapid demolding and palletization within 10–20 min. The study was designed as a process-validation campaign under real industrial production conditions (LOREV 1010/A), combined with an initial technical characterization of the manufactured units. The experimental program focused on manufacturing feasibility and on the initial physical and mechanical characterization of the prefabricated elements, including aggregate granulometric control, dry density, normalized compressive strength, and microstructural observations. Under the selected process conditions, the units reached normalized compressive strength values of up to 2.90 N/mm² and dry density values of approximately 1228 kg/m³, indicating technical suitability for non-load-bearing applications. From a process-route perspective, the cement-free formulation and the use of gypsum-based aggregates support the technical plausibility of a more circular construction system. The environmental and economic implications of the proposed system are discussed from a preliminary process perspective and should be quantified in future life cycle and techno-economic assessments. Full article

Inorganic magnesium potassium phosphate (MKP) coatings offer rapid, zero-volatile organic compound (VOC) corrosion protection for steel structures. However, their application is impeded by insufficient mechanical strength and limited barrier durability. This study integrates calcium sulfate whiskers (CSWs) into a sprayable MKP matrix. Unlike conventional polymeric or metallic fibers, CSWs demonstrate excellent chemical compatibility with the MKP matrix, enabling a dual-enhancement mechanism. The optimal formulation, containing 15 wt.% CSWs, boosts the 28-day compressive strength by 35% and the bond strength by 39%. Electrochemical analysis shows a 93.6% increase in coating resistance (R_f), indicating an improved physical barrier against corrosive species, along with a 52% reduction in corrosion current density. These improvements result from fiber bridging and a dissolution–reprecipitation process that densifies the whisker–matrix interface. Nevertheless, an excessive amount of CSW (20 wt.%) disrupts the matrix continuity and reduces performance. This work presents a high-strength, zero-VOC, spray-applied coating with a novel dual-enhancement mechanism for durable steel protection in aggressive environments. 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

Ferronickel slag, as a major solid waste in the stainless-steel industry, poses a serious threat to the environment due to its large-scale production and low utilization rate. In this study, magnesium oxide in the ferronickel slag was leached out and converted into high-purity magnesium sulfate, while the leach residue was utilized for cement clinker production. During the complete utilization of ferronickel slag, the Mg leaching efficiency reached 90.75% and was significantly enhanced by reducing the particle size of the ferronickel slag with H₂SO₄ solution as the sole solvent. High-purity magnesium sulfate with a purity of 99.92% was prepared from the leachate through a multi-step process involving primary crystallization, purification, and secondary crystallization. The leach residue, accounting for 68.20% of the original mass, was primarily composed of 79.4 wt% SiO₂ and less than 6.1 wt% MgO and is used as a key raw material in the production of Portland cement. Sintering temperature significantly influenced the structure and properties of the resulting cement. Both the Portland clinker and cement were successfully produced at sintering temperatures of 1400 °C and 1450 °C when the leach residue was used as a primary raw material, with well-developed cementitious phases of calcium silicate and aluminate formed during calcination. The setting time, soundness, and compressive and flexural strengths of the hardened C1400 and C1450 mortars met the requirements specified in relevant standards. Through this integrated process, the overall utilization rate of the ferronickel slag reached 100%. Based on a preliminary estimate, full utilization of the annual ferronickel slag production in China could substitute at least 19.5 million tons of magnesite and 15.0 million tons of silica and reduce CO₂ emissions by 10.3 million tons. Full article

Expansive or soft soils cause significant geotechnical issues for foundations and subgrades because they show swell–shrink behaviour under wet and dry conditions. These volume changes can result in cracking, heaving, uneven settlement, and structural or pavement damage, ultimately increasing maintenance and repair costs. While traditional Portland cement and lime stabilisers effectively enhance soil strength and reduce swell–shrink behaviour, the cement production process is responsible for only approximately 7%–8% of global CO₂ emissions, prompting a transition toward sustainable alternatives. This comprehensive review consolidates recent advancements in soil stabilisation using industrial by-products, such as fly ash, ground granulated blast furnace slag (GGBS), steel slag, cement kiln dust, silica fume, bottom ash, red mud, waste foundry sand, brick dust, calcium carbide residue, water treatment sludge, etc. These materials leverage pozzolanic and latent hydraulic properties to form C-A-H, C-S-H, and N-A-S-H gels, thereby densifying the soil microstructure, improving CBR (%), UCS, and reducing plasticity and swelling potential. Optimisation studies indicate that industrial waste stabilisers often match or exceed conventional binder performance, GGBS-steel slag combinations yielding 105% higher UCS than ordinary Portland cement, and silica fume enhances cement-stabilised soils by 22% at reduced dosages. However, inherent compositional variability, long-term durability concerns including sulfate attack and freeze–thaw degradation, and the absence of standardised design guidelines restrict large-scale implementation. This review integrates mechanistic, microstructural, and sustainability insights, highlighting the need for durability research, standardised methods, and large-scale field validation to advance industrial waste-based stabilisation within circular construction practices in geotechnical engineering. Full article

Phosphogypsum is one of the most widely produced gypsum-containing wastes. Therefore, researchers worldwide are exploring ways to recycle them. It is most often considered as an alternative to natural gypsum in the production of calcium sulfate hemihydrate. There are also isolated studies aimed at producing insoluble anhydrite (CaSO₄ II) from phosphogypsum. Compared to hemihydrate, anhydrite is characterized by greater strength and water resistance, and compared to Portland cement, it demonstrates lower energy consumption and CO₂ emissions during production. This study examined the possibility of phosphoanhydrite binder (CaSO₄ II) synthesis by calcination at 600, 800, and 1000 °C of phosphogypsum from four different industrial plants. Phosphoanhydrite binders capable of self-hardening, without the use of special additives, were synthesized. Their maximum strength at 28 days reached 57 MPa, and 69 MPa at 90 days. New data have been obtained regarding the influence of initial phosphogypsum characteristics and calcination temperature on the properties of CaSO₄ II and the hardened phosphoanhydrite paste. Full article

Synthetic biomaterials used as bone graft extenders (BGE) in spinal fusion surgery can supplement but do not replace autologous bone. This pilot study evaluated a calcium sulfate/hydroxyapatite (CaS/HA) material as an antibiotic-eluting BGE and a carrier for bone morphogenetic protein-2 (BMP-2) in a rabbit posterolateral lumbar (L4–L5) spinal fusion model (PLF). Pre-set CaS/HA beads were loaded with tobramycin (TOB) and tested for in vitro antibiotic release and antibacterial activity against Staphylococcus aureus. For the in vivo PLF study, CaS/HA beads were used in two treatment strategies: (1) CaS/HA + TOB + autograft (left side) and (2) CaS/HA + BMP-2 (right side). Serum levels of TOB were quantified and spinal fusion was evaluated after 12 weeks. TOB exhibited a rapid initial release, followed by a decline below detectable levels after 6 h in vitro and 48 h in vivo. TOB-loaded CaS/HA beads demonstrated in vitro antibacterial activity for 19 days. In the PLF study, 5/6 and 6/6 specimens were fused radiologically in the TOB and BMP groups, respectively, and 100% using mechanical testing. Micro-CT analysis showed no significant difference in bone volume between the TOB and BMP-2 groups (364 ± 84 vs. 479 ± 95 mm³). Histology verified continuous bone bridging in both groups. Our in vitro findings indicate that locally added TOB could protect the CaS/HA material from bacterial colonization and did not adversely impact the CaS/HA material negatively to act as BGE. The addition of low-dose BMP-2 to the CaS/HA material proved effective in building bone without the need to harvest autologous bone. In summary, this pilot PLF study demonstrates that the tested CaS/HA material combined with BMP-2 could replace autologous bone harvesting in spinal fusion surgery. Addition of TOB could potentially protect the material from bacterial colonization during the early post-operative period but further studies in infection models are warranted. Full article

Calcareous interbeds are widely developed in marine clastic sequences, where laterally continuous, tight calcareous interbeds act as critical controls on the formation of lithologic traps and the distribution of oil. However, the genetic mechanisms and development models of these interbeds, particularly under deep-burial conditions subject to complex fluid interactions, remain poorly understood. Using the Donghe Sandstone in the Hade Oilfield (Tarim Basin) as a case study, this paper investigates the genetic evolution of calcareous interbeds via an integrated approach combining core observation, thin-section petrography, scanning electron microscopy (SEM), stable isotope analysis, fluid inclusion microthermometry, and heavy fraction analysis. The results indicate that: (1) The carbonate cements within the interbeds are compositionally complex, dominated by calcite but characterized by a diagnostic assemblage of anhydrite, ferroan calcite, and ankerite. (2) During the depositional to shallow burial stages, seawater evaporation and meteoric freshwater influx led to the supersaturation of calcium-rich pore waters near the surface. This facilitated the precipitation of early cement assemblages, which are predominantly of freshwater origin and consist mainly of non-ferroan calcite nodules, dolomite, and anhydrite. (3) During the deep burial stage, the injection of high-salinity brines and organic acid decarboxylation triggered Thermochemical Sulfate Reduction (TSR). This process caused the extensive consumption of the pre-existing anhydrite and the formation of authigenic pyrite, followed by the tight occlusion of remaining porosity through the precipitation of late-stage ferroan calcite and ankerite. (4) In the broad slope setting, these tight calcareous interbeds constitute effective flow barriers, resulting in a stepped distribution of the oil–water contact. Within the reservoir compartments segmented by these interbeds, crude oil maturity exhibits a distinct inversion (i.e., higher maturity below the interbeds and lower maturity above), confirming the critical sealing capacity of the interbeds during hydrocarbon accumulation. Ultimately, this study establishes a genetic model coupling calcareous interbed development with deep-burial fluid alteration, providing new geological insights for predicting subtle traps in marine sandstone reservoirs. Full article