Search Results (265)

Quarry dust (QD) landfill causes environmental issues that cannot be ignored. In this study, we systematically explore its potential application as a supplementary cementitious material (SCM) in cemented paste backfill (CPB), revealing the activated mechanism of modified QD (MQD) and exploring the hydration process and workability of CPB containing QD/MQD. The experimental results show that quartz, clinochlore and amphibole components react with CaO to form reactive dicalcium silicate (C₂S) and amorphous glass phases, promoting pozzolanic reactivity in MQD. QD promotes early aluminocarbonate (M_c) formation through CaCO₃-derived CO₃²⁻ release but shifts to hemicarboaluminate (H_c) dominance at 28 d. MQD releases active Al³⁺/Si⁴⁺ due to calcination and deconstruction, significantly increasing the amount of ettringite (AFt) in the later stage. With the synergistic effect of coarse–fine particle gradation, MQD-type fresh backfill can achieve a 161 mm flow spread at 20% replacement. Even if this replacement rate reaches 50%, a strength of 19.87 MPa can still be maintained for 28 days. The good workability and low carbon footprint of MQD-type backfill provide theoretical support for—and technical paths toward—QD recycling and the development of low-carbon building materials. Full article

This study focuses on the clastic reservoir in the first member of Yaojia Formation within Qijia-Gulong Sag, Songliao Basin. The results indicate that the reservoir in the study area develops within a shallow-water delta sedimentary system. The dominant sedimentary microfacies comprise underwater distributary channels, mouth bars, and sheet sands. Among these, the underwater distributary channel microfacies exhibits primary porosity ranging from 15.97% to 17.71%, showing the optimal reservoir quality, whereas the sheet sand microfacies has a porosity of only 7.45% to 12.08%, indicating inferior physical properties. During diagenesis, compaction notably decreases primary porosity via particle rearrangement and elastic deformation, while calcite cementation and quartz overgrowth further occlude pore throats. Although dissolution can generate secondary porosity (locally up to 40%), the precipitation of clay minerals tends to block pore throats, leading to “ineffective porosity” (permeability generally < 5 mD) and overall low-porosity and low-permeability characteristics. Carbon–oxygen isotope analysis reveals a deficiency in organic acid supply in the study area, restricting the intensity of dissolution alteration. Reservoir quality evolution is dominantly governed by the combined controls of sedimentary microfacies and diagenesis. This study emphasizes that, within shallow-water delta sedimentary settings, the material composition of sedimentary microfacies and the dynamic equilibrium of diagenetic processes jointly govern reservoir property variations. This insight provides critical theoretical support for understanding diagenetic evolution mechanisms in clastic reservoirs and enabling precise prediction of high-quality reservoir distribution. Full article

Red sandstones of the Cambrian age are globally distributed and represent an important sedimentation phase during this critical time interval. Their sedimentology and geochemistry can provide key information about the sedimentation style, paleoclimatic conditions, and weathering trends during the Cambrian. In the Salt Range of Pakistan, the Khewra Sandstone constitutes the Lower Cambrian strata and consists of red–maroon sandstones with minor siltstone and shale in the basal part. Cross-bedding, graded bedding, ripple marks, parallel laminations, load casts, ball and pillows, desiccation cracks, and bioturbation are the common sedimentary features of the formation. The sandstones are fine to medium to coarse-grained with subangular to subrounded morphology and display an overall coarsening upward trend. Petrographic analysis indicates that the sandstones are sub-arkose and sub-lithic arenites, and dolomite and calcite are common cementing materials. X-ray Diffraction (XRD) analysis indicates that the main minerals in the formation are quartz, feldspars, kaolinite, illite, mica, hematite, dolomite, and calcite. Geochemical analysis indicates that SiO₂ is the major component at a range of 53.3 to 88% (averaging 70.4%), Al₂O₃ ranges from 3.1 to 19.2% (averaging 9.2%), CaO ranges from 0.4 to 25.3% (averaging 7.4%), K₂O ranges from 1.2 to 7.4% (averaging 4.8%), MgO ranges from 0.2 to 7.4% (averaging 3.5%), and Na₂O ranges from 0.1 to 0.9% (averaging 0.4%), respectively. The results of the combined proxies indicate that the sedimentation occurred in fluvial–deltaic settings under overall arid to semi-arid paleoclimatic conditions with poor to moderate chemical weathering. The Khewra Sandstone represents the red Cambrian sandstones on the NW Indian Plate margin of Gondwana and can be correlated with contemporaneous red sandstones in the USA, Europe, Africa, Iran, and Turkey (Türkiye). Full article

Quality requirements for mineral aggregate for concrete used to construct pavement for busy highways are high because of the fatigue traffic loads and environmental exposure. The use of local aggregate for infrastructure projects could result in important sustainability improvements, provided that the concrete’s durability is assured. The objective of this study was to identify the potential alkaline reactivity of local greywacke aggregate and select appropriate mitigation measures against the alkali–silica reaction. Experimental tests on concrete specimens were performed using the miniature concrete prism test at 60 °C. Mixtures of coarse greywacke aggregate up to 12.5 mm with natural fine aggregate of different potential reactivity were evaluated in respect to the expansion, compressive strength, and elastic modulus of the concrete. Two preventive measures were studied—the use of metakaolin and slag-blended cement. A moderate reactivity potential of the greywacke aggregate was found, and the influence of reactive quartz sand on the expansion and instability of the mechanical properties of concrete was evaluated. Both crystalline and amorphous alkali–silica reaction products were detected in the cracks of the greywacke aggregate. Efficient expansion mitigation was obtained for the replacement of 15% of Portland cement by metakaolin or the use of CEM III/A cement with the slag content of 52%, even if greywacke aggregate was blended with moderately reactive quartz sand. It resulted in a relative reduction in expansion by 85–96%. The elastic modulus deterioration was less than 10%, confirming an increased stability of the elastic properties of concrete. 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

In this study, the possibility of using cement bypass dust as a cement additive was investigated. The utilization of cement bypass dust remains a major problem in cement production, as huge amounts of it are stored in landfills. In this study, a hydrothermal treatment is proposed to modify the properties of this dust and to expand its use. Hydrothermal treatment with pure bypass dust and quartz was carried out to achieve a CaO/SiO₂ ratio of 1 to 2. Samples were synthesized at 200 °C for 2, 4, 8, and 24 h. To examine the influence of the hydrothermal treatment on cement properties, a sample with a CaO/SiO₂ ratio of 1, hydrothermally treated for 8 h, was selected. This study employed XRD, XRF, DSC-TG, and isothermal calorimetry. Most of the target synthesis products, e.g., tobermorite and calcium silicate hydrates, formed after 8 h of sample synthesis, during which quartz was added to bypass dust and a CaO/SiO₂ ratio of 1 was achieved. An examination of the composition of the liquid medium following hydrothermal processing showed that almost all chlorine passed into the liquid medium, while some K₂O remained in the solid synthesis product. The synthesized additive is an effective catalyst for the hydration of Portland cement. After a 28-day curing period, specimens incorporating modified bypass dust replacing up to 10% of the Portland cement by weight demonstrated compressive strengths comparable to, or surpassing, those of specimens composed exclusively of Portland cement. Full article

The investigation of the pore structure and fractal characteristics of coal-bearing shale is critical for unraveling reservoir heterogeneity, storage-seepage capacity, and gas occurrence mechanisms. In this study, 12 representative Upper Paleozoic coal-bearing shale samples from the Yangquan Block of the Qinshui Basin were systematically analyzed through field emission scanning electron microscopy (FE-SEM), high-pressure mercury intrusion, and gas adsorption experiments to characterize pore structures and calculate multi-scale fractal dimensions (D₁–D₅). Key findings reveal that reservoir pores are predominantly composed of macropores generated by brittle fracturing and interlayer pores within clay minerals, with residual organic pores exhibiting low proportions. Macropores dominate the total pore volume, while mesopores primarily contribute to the specific surface area. Fractal dimension D₁ shows a significant positive correlation with clay mineral content, highlighting the role of diagenetic modification in enhancing the complexity of interlayer pores. D₂ is strongly correlated with the quartz content, indicating that brittle fracturing serves as a key driver of macropore network complexity. Fractal dimensions D₃–D₅ further unveil the synergistic control of tectonic activity and dissolution on the spatial distribution of pore-fracture systems. Notably, during the overmature stage, the collapse of organic pores suppresses mesopore complexity, whereas inorganic diagenetic processes (e.g., quartz cementation and tectonic fracturing) significantly amplify the heterogeneity of macropores and fractures. These findings provide multi-scale fractal theoretical insights for evaluating coal-bearing shale gas reservoirs and offer actionable recommendations for optimizing the exploration and development of Upper Paleozoic coal-bearing shale gas resources in the Yangquan Block of the Qinshui Basin. Full article

The Carboniferous–Permian tight sandstone gas reservoirs in the Shenfu area of the Ordos Basin in China are characterized by the widespread development of multiple formations. However, significant differences exist among the tight sandstones of different formations, and their formation mechanisms and key controlling factors remain unclear, hindering the effective selection and development of favorable tight gas intervals in the study area. Through comprehensive analysis of casting thin section (CTS), scanning electron microscopy (SEM), cathodoluminescence (CL), X-ray diffraction (XRD), particle size and sorting, porosity and permeability data from Upper Paleozoic tight sandstone samples, combined with insights into depositional environments, burial history, and chemical reaction processes, this study clarifies the characteristics of tight sandstone reservoirs, reveals the key controlling factors of reservoir quality, confirms the differential evolutionary mechanisms of tight sandstone of different formations, reconstructs the diagenetic sequence, and constructs an evolution model of reservoir minerals and porosity. The research results indicate depositional processes laid the foundation for the original reservoir properties. Sandstones deposited in tidal flat and deltaic environments exhibit superior initial reservoir qualities. Compaction is a critical factor leading to the decline in reservoir quality across all formations. However, rigid particles such as quartz can partially mitigate the pore reduction caused by compaction. Early diagenetic carbonate cementation reduces reservoir quality by occupying primary pores and hindering the generation of secondary porosity induced by acidic fluids, while later-formed carbonate further densifies the sandstone by filling secondary intragranular pores. Clay mineral cements diminish reservoir porosity and permeability by filling intergranular and intragranular pores. The Shanxi and Taiyuan Formations display relatively poorer reservoir quality due to intense illitization. Overall, the reservoir quality of Benxi Formation is the best, followed by Xiashihezi Formation, with the Taiyuan and Shanxi Formations exhibiting comparatively lower qualities. Full article

The strength parameters of fault gouge are critical factors that influence sealing capacity and fault reactivation in underground gas storage reservoirs. This study investigates the shear characteristics of remolded fault gouge under varying hydro-mechanical conditions, focusing on the coupled influence of water content and cementation. Sixty fault gouge samples are prepared using a mineral mixture of quartz, montmorillonite, and kaolinite, with five levels of water content (10–30%) and three cementation degrees (0%, 1%, 3%). Direct shear tests are conducted under four normal stress levels (100–400 kPa), and microstructural characteristics are examined using SEM. The results show that shear strength and cohesion exhibit a non-monotonic trend with water content, increasing initially and then decreasing, while the internal friction angle decreases continuously. Higher cementation degrees not only enhance shear strength and reduce the softening effect caused by water but also shift the failure mode from ductile sliding to brittle, cliff-type rupture. Moreover, clay content is found to modulate the degree—but not the trend—of strength parameter responses to water and cementation variations. Based on the observed mechanical behavior, a semi-empirical shear strength prediction model is developed by extending the classical Mohr–Coulomb criterion with water–cementation coupling terms. The model accurately predicts cohesion and internal friction angle as functions of water content and cementation degree, achieving strong agreement with experimental results (R² = 0.8309 for training and R² = 0.8172 for testing). These findings provide a practical and interpretable framework for predicting the mechanical response of fault gouge under complex geological conditions. Full article

Traditional cementitious coating materials struggle to meet the performance criteria for protective coatings in complex environments. This study developed a polymer-modified cement-based coating material with polymer, silica fume (SF), and quartz sand (QS) as the principal admixtures. It also investigated the influence of material composition on the coating’s mechanical properties, durability, interfacial bond characteristics with concrete, and the durability enhancement of coated concrete. The results demonstrated that compared with ordinary cementitious coating material (OCCM), the interfacial bonding performance between 3% Styrene Butadiene Rubber Powder (SBR) coating material and concrete was improved by 42%; the frost resistance and sulfate erosion resistance of concrete protected by 6% polyurethane (PU) coating material were improved by 31.5% and 69.6%. The inclusion of polymers reduces the mechanical properties. The re-addition of silica fume can lower the porosity while increasing durability and strength. The coating material, mixed with 12% SF and 6% PU, exhibits mechanical properties not lower than those of OCCM. Meanwhile, the interfacial bonding performance and durability of the coated concrete have been improved by 45% and 48%, respectively. The grey relational analysis indicated that the coating material with the best comprehensive performance is the one mixed with 12% SF + 6% PU, and the grey correlation degree is 0.84. Full article

This work focuses on the design of concrete for the construction of winemaking tanks, as well as coating behaviour and stability of the systems in wine immersion. More specifically, alternative laboratory concrete mixtures were investigated by replacing cement with natural pozzolan and using silicate aggregates and quartz sand as filler in order to obtain self-compacting concrete of strength class C 20/25. The optimal mixture was selected and further tests were carried out on the mechanical properties of permeability, durability and thermal conductivity. Three coatings and plain concrete were tested for their leachability of heavy metals in wine. The results show that the selected composition with 20% cement replacement by natural pozzolan has the desired workability and strength and is comparable to a reference concrete without natural pozzolan. The leachability tests show that heavy metals do not leach out upon contact with wine, but only calcium and potassium oxide, which can be easily addressed by coating or treating the surface of the concrete. Also, the optimum coating did not influence the pH of the wine. Full article

Freeze–thaw damage is a critical durability challenge in cold climates that leads to surface spalling, cracking, and degradation of structural performance. In northern China, the severity of winter conditions further accelerates the degradation of concrete infrastructure. This study investigates the reinforcement of frost-damaged concrete using engineered cementitious composites (ECC) prepared with Yellow River sedimentary sand (YRS), employed as a 100% mass replacement for quartz sand to promote sustainability. The interface bonding performance of ECC-C40 specimens was evaluated by testing the impact of various surface roughness treatments, freeze–thaw cycles, and interface agents. A multi-factor predictive formula for determining interface bonding strength was created, and the bonding mechanism and model were examined through microscopic analysis. The results show that ECC made with YRS significantly improved the interface bonding performance of ECC-C40 specimens. Specimens treated with a cement expansion slurry as the interface agent and those subjected to the splitting method for surface roughness achieves the optimal reinforced condition, exhibited a 27.57%, 35.17%, 43.57%, and 42.92% increase in bonding strength compared to untreated specimens under 0, 50, 100, and 150 cycles, respectively. Microscopic analysis revealed a denser interfacial microstructure. Without an interface agent, the bond interface followed a dual-layer, three-zone model; with the interface agent, a three-layer, three-zone model was observed. Full article

Porous artificial reef materials made of cement used in the offshore area can repair and improve the ecological environment and enrich fishery resources. In this study, quartz sand was used as the aggregate, high-alumina cement as the cementing agent, and crushed particles of waste tires as the modifier to prepare porous cement–polymer composites. Through orthogonal tests, the effects of the aggregate particle size, the ratio of aggregate to cement, the rubber particle size, and the rubber ratio on the strength and permeability of the porous cement–polymer composites were studied. The significant degrees of different influencing factors were analyzed, and an appropriate configuration scheme for the porous cement–polymer composites was proposed. The experimental results show that the quantity of rubber particles added and the particle size of the rubber particles have a relatively large impact on the properties of the porous cement–polymer composites. Through response surface tests, the interactive effects of various factors in the porous cement–polymer composites on the compressive strength and permeability of the material were verified. The microstructure of the porous cement–polymer composites was observed by SEM. The differences in the microstructure and internal structure between the specimens with a low rubber content and large rubber particle size and those with a high rubber content and small rubber particle size were analyzed, and the influence mechanism of the differences in the microstructure and internal structure on the strength and permeability was proposed. Full article

In order to clarify the pore evolution and coupling characteristics with hydrocarbon charging in the deep-buried ultra-tight sandstone reservoirs of the second member of Xujiahe Formation (hereinafter referred to as the Xu 2 Member) on the eastern slope of the Western Sichuan Depression, this study integrates burial history and thermal history with analytical methods including core observation, cast thin section analysis, scanning electron microscopy, carbon-oxygen isotope analysis, and fluid inclusion homogenization temperature measurements. The Xu 2 Member reservoirs are predominantly composed of lithic sandstones and quartz-rich sandstones, with authigenic quartz and carbonates as the main cementing materials. The reservoir spaces are dominated by intragranular dissolution pores. The timing of reservoir densification varies among different submembers. The upper submember underwent compaction during the Middle-Late Jurassic period due to the high ductility of mudstone clasts and other compaction-resistant components. The middle-lower submembers experienced densification in the Late Jurassic period. Late Cretaceous tectonic uplift induced fracture development, which enhanced dissolution in the middle-lower submembers, increasing reservoir porosity to approximately 5%. Two distinct phases of hydrocarbon charging are identified in the Xu 2 Member. The earlier densification of the upper submember created unfavorable conditions for hydrocarbon accumulation. In contrast, the middle-lower submembers received hydrocarbon charging prior to reservoir densification, providing favorable conditions for natural gas enrichment and reservoir formation. Three sweet-spot reservoir development patterns are recognized: paleo-structural trap + (internal source rock) + source-connected fracture assemblage type, paleo-structural trap + internal source rock + late-stage fracture assemblage type, and paleo-structural trap + (internal source rock) + source-connected fracture + late-stage fracture assemblage type. Full article

Urban air pollution poses significant risks to cultural heritage buildings, particularly in polluted megacities like Delhi, India. The Red Fort, a UNESCO World Heritage Site and a symbol of India’s rich history, is highly susceptible to degradation caused by air pollutants. Despite its great importance as an Indian and world heritage site, no studies have focused on characterizing its constituent materials or the degradation phenomena taking place. This study was developed in the framework of the MAECI (Italian Ministry of Foreign Affairs) and the Department of Science and Technology under the Ministry of Science and Technology, India, project: Indo—Italian Centre of Excellence for Restoration and Assessment of Environmental Impacts on Cultural Heritage Monuments. To understand their composition and degradation, Vindhyan sandstone and black crust samples were studied. Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) indicated that the red sandstone predominantly consisted of quartz and microcline, while the black crusts mainly comprised gypsum, bassanite, weddellite, quartz, and microcline. The analysis attributed the formation of gypsum to exogenous sources, such as construction activities and cement factory emissions. This pioneering study provides a basis for further research into the impacts of air pollution on Indian patrimony and promotes conservation strategies. Full article