Search Results (731)

This study developed a sustainable low-carbon cementitious material using calcium carbide residue (CCR) as an alkali activator, combined with ground granulated blast furnace slag (GGBS) and fly ash (FA) to form a composite. The objective was to optimize the CCR dosage and the GGBS-to-FA ratio to enhance the unconfined compressive strength (UCS) of the composite, providing a viable alternative to traditional Portland cement while promoting solid waste recycling. Experiments were conducted with a water-to-binder ratio of 0.55, using six GGBS-to-FA ratios (0:10, 2:8, 4:6, 6:4, 8:2, and 10:0) and CCR contents ranging from 2% to 12%. Results indicated optimal performance at a GGBS-to-FA ratio of 8:2 and an 8% CCR dosage, achieving a peak UCS of 18.04 MPa at 28 days, with 79.88% of this strength reached within just 3 days. pH testing showed that with 8% CCR, pH gradually decreased over the curing period but increased with higher GGBS content, indicating enhanced reactivity. Microstructural analyses (XRD and SEM-EDS) confirmed the formation of hydration products like C-(A)-S-H, significantly improving density and strength. This study shows CCR’s potential as an effective and environmentally friendly activator, advancing low-carbon building materials and resource recycling in construction. Full article

This paper aims to define and identify the Honey Bee Welfare Practices (HBWPs) that beekeepers should adopt within a modern framework for sustainable apiculture. Once identified, HBWPs were categorized according to the Five Domains Model used in other animal species. Drawing on findings of the European BPRACTICES Horizon 2020 project, we identified, for the first time, 243 HBWPs: while all practices were considered impacting the mental state domain, 38 were assigned to nutrition/hydration, 90 to environment, 220 to health, and 50 to behavior. The proposed HBWPs aim to fill existing gaps by introducing a new approach that more fully respects honey bee behavior and helps prevent unnecessary suffering for each bee and the whole beehive at the same time. Future efforts should focus on maximizing welfare benefits within the One Welfare framework, moving beyond the previously considered One Health perspective. This welfare-oriented focus benefits honey bees, supports beekeepers, and promotes environmental sustainability, aligning with the principles of One Welfare. Full article

Using solid waste-based materials, such as recycled building aggregate (RCA), preparing 3D-printed materials can reduce costs but increase the water–cement ratio of the printed material, which reduces its mechanical performance. In order to solve the problem of mechanical properties decline caused by an increase in the w/c ratio, this experiment found that adding calcined salt mud (CSM) to the printing materials and changing the water-to-cement ratio from 0.37 to 0.4 CSM can ensure that the compressive strength of the printing materials remains basically unchanged. Moreover, through TG, SEM, and other microscopic data, it can be seen that calcium hydroxide in CSM can not only participate in the synergistic reaction of ethylene/vinyl acetate copolymer (EVA) and dust ash (DA), produce more NaOH, and promote the hydration of granulated blast furnace slag (GBFS) but also promote the formation of ettringite together with SO₄²⁻ in solution, optimizing pore size distribution. Full article

Nano metakaolin (NMK) has attracted considerable interest for its potential to improve the durability of cementitious materials. However, the effect of NMK on the splitting tensile performance of concrete has not been systematically investigated. This study investigates the splitting tensile performance of NMK concrete and analyzes its failure behavior under splitting load. Different NMK dosages (0%, 1%, 3%, 5%, and 7%) were considered, and splitting tensile tests were conducted. The crack propagation process, crack width, and crack growth rate on the surface of NMK concrete during the splitting tensile test are analyzed using the Digital Image Correlation (DIC) method. The mechanisms by which NMK affects the splitting tensile performance of concrete were examined using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), and Thermogravimetric Analysis (TG). The results indicate that the incorporation of NMK enhances the splitting tensile performance of concrete. Concrete with 5% NMK addition exhibited the highest splitting tensile strength, with an increase of 17.4% compared to ordinary concrete. NMK improved the cracking resistance and overall integrity under splitting tensile load. With 5% NMK addition, the surface crack length, width, and main crack propagation rate of the concrete decreased by 4.5%, 35.3%, and 29.6%, respectively. NMK contributed to a denser internal structure of the concrete, promoted the formation of C-S-H gel, and increased the degree of cement hydration. Moreover, a lower thickness and Ca/Si ratio of interfacial transition zone (ITZ) were observed in NMK concrete. The ITZ thickness and Ca/Si ratio of concrete with 5% NMK were reduced by 64.4% and 85.4%, respectively, compared to ordinary concrete. In summary, the influence mechanism of NMK addition on the splitting tensile strength and failure behavior of concrete is explored in this study, providing experimental data to support the application of NMK concrete in practical engineering. Full article

Hydraulic fracturing of deep, high-temperature reservoirs poses challenges due to elevated temperatures and high fracture pressures. Conventional polymer fracturing fluid (QCL) has high viscosity upon adding cross-linking agents and significantly increases wellbore friction. This paper examines a polymer fracturing fluid with pH response and low friction. Experimental results indicate that cross-linking occurs quickly in acid, while alkali can slow the cross-linking process and reduce friction. Sodium carbonate (Na₂CO₃) serves as an effective candidate. An optimized formulation consisting of “salt + pH + polymer + cross-linking agent” is proposed in two stages: low viscosity for fracture generation and high viscosity for sand transport. PH control enhances polymer hydration, increasing sand-carrying in the low-viscosity stage. Scanning electron microscopy (SEM) reveals that the fluid’s structure varies with pH, showing that alkali promotes a stable network structure. Infrared spectroscopy (IR) shows that higher pH increases negative charges of the polymer chains, which enhances their hydrodynamic radius, slightly raises viscosity, and enhances sand carrying. Field tests confirm the formulation’s effectiveness, leading to lower operating pressures, stable sand transport, and notable production, averaging 107.57 m³ of oil and 276 m³ of gas per day. Overall, this research provides low-friction solutions for the efficient development of deep reservoirs. Full article

Fly ash–cement composite backfill slurry, prepared by partially replacing cement with fly ash, has been demonstrated to effectively reduce the mine backfill costs and carbon emissions associated with cement production. However, the use of fly ash often results in insufficient early and medium-term strength of the backfill material. To address the demand for high medium-term strength in backfill materials under continuous mining and backfilling conditions, this study developed a silica fume–fly ash–cement composite backfill slurry. The effects of varying silica fume contents on the slurry’s flowability, uniaxial compressive strength, microstructure, and pore characteristics were systematically investigated. The results showed that increasing the silica fume content significantly reduced the slurry’s flowability. However, at a silica fume content of 5%, the slurry achieved optimal medium-term strength, with a 14-day uniaxial compressive strength of 3.98 MPa, representing a 25% improvement compared to the control group. A microstructural analysis revealed that a moderate silica fume content promoted the formation of calcium silicate hydrate gel, filled micropores, and optimized the pore structure, thereby enhancing the overall strength and durability of the material. Conversely, an excessive silica fume content above 5% led to a marked decrease in both flowability and strength. Based on a comprehensive evaluation of silica fume’s effects on the flowability, strength, and microstructure, the optimal silica fume content was determined to be 5%. This study provides a theoretical basis and practical guidance for improving the efficiency of continuous mining and backfilling operations, and for designing high-performance backfill materials suitable for continuous mining and filling conditions. Full article

An alternative approach to reducing the clinker factor, i.e., worldwide CO₂ emissions resulting from the production of composite cement, is to replace these materials with supplementary aluminosilicate-based materials that promote the formation of alkali-activated cements, whose elevated temperature resistance, limited permeability, strong binding properties, excellent durability, high chemical corrosion resistance, confinement of toxic waste, and environmentally low impact have attracted a lot of attention in the cement industry. The principal aluminosilicate-based supplementary materials (SCMs) used in the cement industry are fly ash and blast-furnace slag. Recently, limestone has been proposed for use in alkali-activated cement to improve mechanical resistance and promote nucleation sources for the hydration of hybrid gels. In the current research work, the effect of 5 and 10 wt% limestone additions to slag and fly ash/slag alkali-activated cements with NaOH-4M was studied to evaluate the mechano-chemical and microstructural properties of alkali-activated cement. The effect of limestone was studied using mechanical resistance, XRD, FTIR, SEM-EDS, and calorimetry methods. The XRD, FTIR, and SEM-EDS results demonstrated the formation of portlandite Ca(OH)₂ after the activator solution’s reaction with limestone. The limestone’s dissolution in Ca²⁺ contributes to hybrid gel formation ((N, C)-A-S-H, N-A-S-H, and C-A-S-H), resulting in compressive strength higher than 20 MPa, the recommended resistance for commercial cement. Full article

Understanding the enhancing mechanisms of graphene oxide (GO) on the pore structure characteristics in the interfacial transition zone (ITZ) plays a crucial role in cemented waste rock backfill (CWRB) nanoreinforcement. In the present work, an innovative method based on metal intrusion techniques, backscattered electron (BSE) images, and deep learning is proposed to analyze the micro/nanoscale characteristics of microstructures in the GO-enhanced ITZ. The results showed that the addition of GO reduced the interpore connectivity and the porosity at different pore throats by 53.5–53.8%. GO promotes hydration reaction in the ITZ region; reduces pore circularity, solidity, and aspect ratio; enhances the mechanical strength of CWRB; and reduces transport performance to form a dense microstructure in the ITZ. Deep learning-based analyses were then proposed to classify and recognize BSE image features, with a high average recognition accuracy of 95.8%. After that, the deep Taylor decomposition (DTD) algorithm successfully located the enhanced features of graphene oxide modification in the ITZ. The calculation and verification of the typical pore optimization area of the location show that the optimization efficiency reaches 9.6–9.8%. This study not only demonstrated the deepening of the enhancement effect of GO on the pore structure in cement composites and provided new insights for the structural modification application of GO but also revealed the application prospect of GO in the strengthening of CWRB composites and solid waste recycling. Full article

The Ethylene Diamine Tetra-acetic Acid (EDTA) titration test is widely used for determining cement content, but its reliability is influenced by the hydration process of cement, which is affected by factors such as water content and hydration time. Despite their importance, these factors have received limited attention in existing research. This study explores the relationships between the volume of titrant required for stabilization, cement content, water content, and hydration time. Using a regression orthogonal test, the primary and secondary relationships, as well as the interdependencies among these factors, are analyzed. Results reveal a negative linear relationship between the titrant volume and both water content and hydration time. Cement content, water content, and hydration time are identified as the most significant factors, with minimal interdependencies observed. Within the test parameters, calculated values exhibit an error margin below 2.4%. Deviations of 2.9% in water content and 86 min in hydration time correspond to an approximate 0.5% change in cement content. These findings offer valuable insights for optimizing cement content detection in Controlled Low-Strength Material (CLSM) mixes, promoting more sustainable construction practices. Full article

This study examines the impact of sodium citrate and a plasticizing additive, along with their sequential introduction into a cement slurry or concrete mix, on the heat evolution of the cement slurry, the microstructure, phase composition of the cement paste, and the compressive strength of fine-grained concrete. The binder used in this research was a blended binder consisting of 90% Portland cement and 10% calcium aluminate cement. This type of binder is characterized by an increased heat evolution and accelerated setting time. The addition of sodium citrate at 5% of the binder mass alters the phase composition of newly formed compounds by increasing the quantity of AFt and AFm phases. The presence of sodium citrate significantly delays the hydration process of tricalcium silicate by a factor of 3.3. Initially, it accelerates belite hydration by 31.6%, but subsequently slows it down, with a retardation of 43.4% observed at 28 days. During the hardening process, the hydration of tricalcium aluminate and tetracalcium aluminoferrite is accelerated throughout the hardening process, with the maximum acceleration occurring within the first 24 h. During the first 24 h of hydration, the dissolution rates of tricalcium aluminate and tetracalcium aluminoferrite were 40.7% and 75% faster, respectively. Sodium citrate enhances heat evolution during the initial 24 h by up to 4.3 times and reduces the induction period by up to 5 times. Furthermore, sodium citrate promotes early strength development during the initial curing period, enhancing compressive strength by up to 6.4 times compared to the reference composition. Full article

This research investigates the use of recycled diatomaceous earth (diatomite) from the wine, beer, and oil industries as supplementary cementitious materials in cement-based mixtures. This study aims to reduce embodied energy and promote circular economy practices by incorporating these industrial by-products. The research evaluates the compressive strength, durability, and pozzolanic activity of the mixtures over 7, 28, and 90 days of hydration. The results demonstrate that uncalcined diatoms from wine and oil showed lower compressive strength than natural diatomite, whereas calcination at 500 °C significantly improved performance. Beer diatoms exhibited the lowest mechanical strength because of the organic matter content in their composition. The incorporation of quicklime failed to induce pozzolanic activity in uncalcined diatoms; however, calcination at 500 °C led to improved long-term performance, highlighting the importance of heat treatment for activating diatoms’ pozzolanic properties. This study concludes that recycled diatoms, particularly when calcined, have potential as sustainable cementitious materials. Full article

The cement industry significantly contributes to global CO₂ emissions, posing several challenges for a future low-carbon economy. In order to achieve the target established by the European Sustainable Development Goals of reaching carbon neutrality by 2050, the European Cement Association (Cembureau) has devised a comprehensive roadmap based on five key approaches, referred to as the 5C strategies. Portland clinker is one of the crucial concerns, since its production emits over 60% of the cement manufacturing emissions. Therefore, supplementary cementitious materials (SCMs) to partially replace clinker content in cement have gained significant attention in providing alternatives to traditional clinker in cement production. This paper evaluates the potential of Portuguese calcined clays (CCs) as viable substitutes for clinker to enhance sustainability in cement manufacturing. More than 50 clays were characterised through chemical and mineralogical analyses to assess their reactivity and suitability for calcination using the strength activity index (SAI), along with XRD, XRF, and TGA techniques. This study investigated the calcination conditions that provide the best clay reactivity, which were subsequently used for calcination. This investigation is part of a project to evaluate the behaviour of calcined clays through mechanical, hydration, and durability properties. The findings indicate that Portuguese calcined clays exhibit promising pozzolanic activity. Furthermore, these clays could significantly reduce CO₂ emissions and raw material consumption in cement production. This research underscores the potential of local calcined clays as a sustainable clinker substitute, promoting eco-friendly practices in the construction industry. Full article

Research progress of carbon dioxide applied for methane exploitation from hydrates is summarized, with a focus on advances in molecular dynamics simulations and their application in understanding the mechanism of carbon dioxide replacement for hydrate exploitation. The potential of carbon dioxide in enhancing energy recovery efficiency and promoting carbon capture and storage is emphasized. An overview is provided of the advancements made in utilizing carbon dioxide for methane hydrate exploitation, highlighting its significance. Subsequently, the theoretical foundations and techniques of molecular dynamics simulations are delved into, encompassing key elements such as statistical ensembles, molecular force fields, and numerical solution methods. Through simulations, various characterization parameters including mean square displacement, radial distribution functions, coordination numbers, angular order parameters, and hydrogen bonds are computed and analyzed, which are crucial for understanding the dynamic changes in hydrate structures and the replacement process. Thorough research and analysis have been conducted on the two possible and widely debated mechanisms involved in the replacement of methane hydrates by carbon dioxide, with a particular emphasis on guest molecular replacement and hydrate reconfiguration. These processes encompass the intricate interactions between carbon dioxide molecules and the cage-like structure of hydrates, as well as the rearrangement and stabilization of hydrate structures. Several key issues surrounding the application of carbon dioxide for methane hydrate exploitation are identified, including the influence of thermodynamic conditions, the selection of auxiliary gases, and other potential factors such as geological conditions and fluid properties. Addressing these issues is crucial for optimizing the extraction process and enhancing economic and environmental benefits. A theoretical foundation and technical reference for the application of carbon dioxide in methane hydrate exploitation are provided, while future research directions and priorities are also outlined. Full article

Carbon capture, utilization and storage are facilitated through carbon dioxide (CO₂) transport. Pipe transportation is the main method for transporting CO₂. However, hydrate blockages reduce transport efficiency in the pipelines, and the throttling devices are the main location of hydrate blockages. In this paper, the mechanism of hydrate formation in the throttling of CO₂-containing trace moisture was investigated. The throttling device in a pipe was mimicked using a cylindrical orifice plate. The work also studied the effects of moisture content, upstream pressure and upstream temperature on hydrate formation. The results indicate that the Joule–Thomson cooling effect is a key contributor, and promotes the condensation of trace moisture, resulting in the free water necessary for hydrate nucleation. Under the effect of gas flow back-mixing, it is easy for the hydrate to adhere to the inner surface of the pipe behind the orifice plate. When the moisture content in the gas increases from 123 μmol/mol to 1024 μmol/mol, the hydrate induction time decreases from infinity to 792 s. However, the moisture content has no effect on the adhesion strength of the hydrate to the inner surface of the pipe. When the initial upstream pressure increases from 2.0 MPa to 3.5 MPa, the hydrate induction time decreases from infinity to 306 s. When the upstream temperature decreases from 291.15 K to 285.15 K, the hydrate induction time decreases from infinity to 330 s. With the decrease in the initial upstream temperature, the adhesion of hydrate particles to the inner surface of the pipe is promoted. This study provides experimental evidence for the characteristics of hydrate formation in the process of CO₂ throttling. Full article

Silica fume (SF) has been widely used in engineering; however, its densification during transportation reduces its original pozzolanic activity. This paper investigates the effects of wet grinding and chemical activation on the mechanical properties and hydration products of silica fume in cement-based materials, revealing the mechanism by which wet grinding improves these properties. The results indicate that wet grinding effectively reduces the particle size of silica fume. Under optimal excitation conditions (250 r/min, 20 min), the median particle size is reduced to 12.1 μm, 2.27 times smaller than before excitation. The 28-day compressive strength of the silica fume cement paste reaches 60.8 MPa, 23.7% higher than that of the reference group. This approach effectively mitigates nano-agglomeration, enhances the pozzolanic activity of silica fume, and promotes AFt and C-S-H gel formation. The findings demonstrate that wet grinding activation can further enhance the utilization rate of silica fume. Full article