Search Results (32)

In order to improve the durability of loess-based composite coal gangue porous planting concrete (LCPC), the effects of fly ash and slag powder content on the durability and microstructure of LCPC were studied. In this paper, fly ash and slag powder were mixed into LCPC, and freeze-thaw cycle and dry-wet cycle tests were carried out. The compressive strength, dynamic elastic modulus, and mass change were used as evaluation indices to determine the optimal mix ratio for LCPC durability. Scanning electron microscopy (SEM) was performed, and the experimental design was carried out with the water–cement ratio, fly ash, and slag powder content as variables. The microstructure characteristics of LCPC were analyzed. The results show that the maximum number of freeze-thaw cycles can reach 35 times and the maximum number of dry-wet cycles can reach 50 when 5% fly ash and 20% slag powder are used. With an increase in the water-cement ratio, the skeleton of the loess gradually became complete, and its structure became more compact. In the micro-morphology diagram, the mixed fly ash and slag powder particles are not obvious, but with an increase in dosage, the size of the cracks and pores gradually decreases. The incorporation of fly ash and slag powder can play a positive role in the durability of LCPC and improvement of its microstructure. The results of this study are crucial for improving the application performance of ecological restoration, soil improvement, and long-term stability of structures, and can provide a scientific basis for the sustainable development of environmentally friendly building materials. Full article

Coal gangue is a fine-grained mineral with nutrient content, which can be used as a potential soil amendment. Nevertheless, current research on using coal gangue to improve soil water and support plant growth is still insufficient. In this study, coal gangue powder (CGP) was added to aeolian sandy soil. We compared the soil hydraulic properties and plant growth of original aeolian sandy soil (CK) and different CGP application rates (10% and 20%). The results indicated that the application of CGP transformed the soil texture from sandy to loamy, significantly reduced soil bulk density and saturated hydraulic conductivity (Ks) values, altered the soil water characteristic curve, enhanced soil water-holding capacity, and increased plant-available water. Compared with the CK group, the emergence rate of alfalfa seeds increased from approximately 50% to over 70% after CGP application. During the growth process, CGP application significantly elevated the net photosynthetic rate, transpiration rate, and stomatal conductance of alfalfa leaves. Rapid fluorescence kinetics monitoring of leaves demonstrated that alfalfa treated with CGP had a higher efficiency in light energy utilization. However, the photosynthetic capacity of leaves did not improve as the CGP application rate increased from 10% to 20%, suggesting that excessive CGP addition did not continuously benefit plant gas exchange. In conclusion, CGP application can improve the soil hydraulic properties of aeolian sandy soil and support plant growth and development, which is conducive to reducing the accumulated amount of coal gangue, alleviating plant water stress, and promoting ecological restoration in arid mining areas. We recommend a 10% addition of coal gangue powder as the optimal amount for similar soils. Full article

In this study, the mechanical properties and failure characteristics of concrete with 10–20 mm recycled coarse aggregate at 0%, 25%, 50%, 75%, and 100% substitution rates were studied. In addition, the influence of coal gangue powder (CGP) on the mechanical properties of concrete was studied under the dosages of 5%, 10%, 15%, and 20%. The research results show that the peak strength of recycled concrete decreases with the increase in the replacement rate of 10–20 mm recycled coarse aggregate. When the replacement rate is 25%, the decrease in strength is the smallest. When the content of CGP increases from 0 to 20%, the peak strength of recycled concrete increases first and then decreases. When the content of CGP is 15%, the peak strength reaches the maximum value. The peak strength increases slightly. The density of pores and cracks in recycled concrete increases with the increase of 10–20 mm recycled coarse aggregate replacement rate. When the substitution rate exceeds 25%, the proportion of cracks increases by nearly 1.7 times. After adding CGP to recycled concrete, the pore density and crack ratio inside a specimen are significantly reduced. When the CGP content exceeds 15%, the crack ratio tends to be stable. When the CGP content is 15%, the crack ratio is 0.519%, which is 23.5% lower than that of the RAC-25 specimen. When the content exceeds 15%, the crack ratio tends to be stable. Full article

To maximize the comprehensive utilization of gangue waste, broken gangue can be used to replace gravel as the coarse aggregate to prepare underground roadway shotcrete, and treated gangue powder can be used for the partial replacement of cement. This not only diminishes the demand for conventional raw materials but also increases the amount of gangue waste disposed. Broken gangue waste was ball-milled for 1 h, 3 h, and 5 h to prepare gangue powder, which was used to partially replace cement. Then, experimental schemes for the performance of shotcrete at the rates of cement replacement of 30%, 40%, and 50% were devised to compare the mineral compositions and microscopic characteristics of shotcrete with the partial replacement of cement with gangue powder. The influences of the partial replacement of cement with gangue powder on the slump, tensile strength, and compressive strength of the shotcrete were revealed. The experimental results revealed an inverse relationship between shotcrete slump and both the cement replacement ratio and the gangue Ball-milling duration. Increasing the cement replacement ratio from 30% to 50% reduced slump by 55.3% (103 mm → 46 mm), while extending the Ball-milling time from 1 h to 5 h decreased it by 33.0% (103 mm → 69 mm). Mechanical properties showed contrasting trends: After a 28-day curing process, compressive and tensile strengths declined by 54.5% (20.18 → 9.18 MPa) and 40.4% (1.56 → 0.93 MPa), respectively, with a higher cement replacement ratio. Conversely, prolonged Ball-milling duration improved the compressive strength by 12.8% (18.68 → 21.07 MPa) and the tensile strength by 34.1% (1.26 → 1.69 MPa). Moreover, the shotcrete meets the strength requirements for engineering applications only when the cement replacement ratio is 30% with gangue ball-milling durations of 3 h and 5 h. The research provides strong support for the performance optimization of gangue-based shotcrete and the improvement of the utilization of gangue waste. Full article

During the extraction and utilization of coal resources, a large amount of CO₂ and coal-based solid wastes (CBSW), such as coal gangue, are generated. To reduce the carbon and waste emissions, an effective approach is to mineralize the CO₂ with the CBSW and then backfill the mineralized materials into the goaf area. However, efficient CO₂ mineralization is challenging due to the low reactivity of coal gangue. To this end, mechanical activation was used for the modification of coal gangue, and the mechanical activation mechanism of coal gangue was revealed from a microcosmic perspective by dry powder laser particle size testing (DPLPST), X-ray diffractometer (XRD) analysis, Fourier-transform infrared spectrometer (FTIR) analysis, and scanning electron microscopy (SEM). The results showed that compared with the unground coal gangue, the average particle size of coal gangue after 0.5 h, 1 h, and 1.5 h milling decreases by 94.3%, 95%, and 95.3%, respectively; additionally, the amorphous structures of the coal gangue after milling increase, and their edges and corners gradually diminish. After the pressure mineralization of coal gangues with different activation times, thermogravimetric (TG) analysis was performed, and the CO₂ mineralization effect of the mechanically activated coal gangue was explored. It is found that the carbon fixation capacity of the coal gangue after 0.5 h, 1.0 h, and 1.5 h mechanical activation is increased by 1.18%, 3.20%, and 7.57%, respectively. Through the XRD and SEM, the mechanism of CO₂ mineralization in coal gangue was revealed from a microcosmic perspective as follows: during the mineralization process, alkali metal ions of calcium and magnesium in anorthite and muscovite are leached and participate in the mineralization reaction, resulting in the formation of stable carbonates such as calcium carbonate. Full article

Coal gangue is a solid waste produced in the coal mining process. During the mining process, mining-induced overburden fractures are a favorable place for the storage of coal gangue; therefore, coal gangue can be incorporated into filling materials for harmless disposal. Overburden isolated grout filling is a better technology for solid waste reduction, which is currently in development. This paper delves into the methodology of large-scale coal gangue disposal, utilizing this specific technology. With reference to fly ash granules and their slurry characteristics that have been previously applied successfully, raw gangue was pulverized and transformed into a slurry. This experiment then investigated the fundamental characteristics of the gangue powder solids and slurry. This study’s findings reveal that the composition types of granule oxides following gangue pulverization closely resemble those of fly ash, with minimal content differences observed between identical oxides. Regarding slurry characteristics, the plastic viscosity of fly ash slurry ranged from 0.45 to 145.2 mPa·s, whereas the plastic viscosity of gangue slurry varied between 2.1 and 56.4 mPa·s. Notably, the stability and fluidity of the gangue slurry surpassed those of the fly ash slurry. Furthermore, regarding the filling efficiency, the compaction coefficient of gangue slurry is less than that of fly ash. Consequently, under identical grouting conditions, a larger mass of solids can be disposed of using gangue slurry compared to fly ash. The research findings facilitate the implementation of a practice involving the overburden isolated grout filling of over million tons of coal gangue in the 21404 working face of the Hulusu coal mine, located in Inner Mongolia, China. This practice has demonstrated a daily filling capacity of up to 4000 t, accumulating to a total gangue filling mass of 1,068,000 t. This study’s findings present a viable and efficient approach to the large-scale, environmentally friendly disposal of coal gangue. Full article

The objective of this research is to fabricate waste-based alkali-activated foams with better properties in a quick time by using energy-efficient techniques such as microwave irradiation. The present study reports the effect of microwave heating parameters, including heating time and output power, on the properties of porous alkali-activated materials (AAMs) that use coal gangue (CG) as a precursor. The effects of concrete waste (CW) content (0–20 wt %) on the performance and microstructure of CG-based AAMs were investigated. Mechanical, thermal, and microstructural investigations were conducted to characterize the obtained materials. The experimental results indicate that the best characteristics of CG-based alkali-activated foams were achieved when microwave power and microwave heating time were 800 W and 10 min, respectively. The foams prepared by adding the waste concrete powder increased stability and showed lower bulk density and thermal conductivity. When the waste concrete powder content was 10 wt %, the CG-based alkali-activated foams showed the best overall performance. At the same time, the mechanical properties of the alkali-activated foams declined only slightly (~9%). The findings of this work provide a basis for further studies on improving the characteristics of CG-based alkali-activated foams due to the physical effect of a microwave field on fresh mortar without the use of a chemical foaming agent while reducing energy consumption in the production process. Full article

Developing green, low-carbon building materials has become a viable option for managing bulk industrial solid waste. This paper presents a kind of all solid waste cementitious material (SWCM), which is made entirely from six common industrial wastes, including carbide slag and silica fume, that demonstrate strong mechanical properties and effectively stabilize aeolian sand (AS). Initially, we investigated the mechanical strength of waste-based cementitious materials in various mix ratios, focusing on their ability to stabilize river sand (RS) and aeolian sand. The results show that it is necessary to use alkaline solid waste carbide slag to provide a suitable reaction environment to achieve the desired strength. In contrast, the low reactivity of coal gangue powder did not contribute effectively to the strength of the cementitious material. Further orthogonal experiments determined the impact of different waste dosages on the strength of stabilized AS. It was found that increasing the amounts of carbide slag, silica fume, and blast furnace slag powder improved strength, while increasing fly ash first increased and then decreased strength. In contrast, higher additions of desulfurization gypsum and coal gangue powder led to a continuous decrease in strength. The optimized mix is carbide slag—desulfurization gypsum—fly ash—silica fume—blast furnace slag powder in a ratio of 4:2:2:3:3. The experimental results using SWCM to stabilize AS indicated a proportional relationship between strength and SWCM content. When the content is ≥20%, it meets the strength requirements for road subbases. The primary hydration products of stabilized AS are C-(A)-S-H, AFt, and CaCO₃. Increasing the SWCM content enhances the reaction degree of the materials, thereby improving mechanical strength. This study highlights the mechanical properties of cementitious materials made entirely from waste for stabilizing AS. It provides a reference for the large-scale utilization of industrial solid waste and practical applications in desert road construction. Full article

This study aims to provide a high-value and environmentally friendly method for the application of coal-based solid waste. Modified fly ash/polyurethane (MFA/PU) and modified coal gangue powder/polyurethane (MCG/PU) composites were prepared by adding different contents of MFA and MCG (10%, 20%, 30%, 40%). At the filler content of 30%, the compressive strengths of MFA/PU and MCG/PU are 84.1 MPa and 46.3 MPa, respectively, likely due to an improvement in interface compatibility, as indicated by scanning electron microscopy (SEM). The MFA/PU and MCG/PU composites present their highest limiting oxygen index (LOI) values of 29% and 23.5%, respectively, when their filler content is 30%. MFA has advantages in improving the LOIs of composites. Cone calorimetry (CCT) and SEM demonstrate that the two composites exhibit similar condensed-phase flame-retardant behaviors during combustion, which releases CO₂ in advance and accelerates the formation of a dense barrier layer. Compared with the MFA/PU composites, the MCG/PU composites could produce a more stable and dense barrier structure. Water quality tests show that heavy metals do not leak from FA and CG embedded in PU. This work provided a new strategy for the safe and high-value recycling of coal-based solid waste. Full article

Coal gangue, as a subgrade filler, is of great significance for the sustainable development of the economy, society, and environment. Particle crushing tests were conducted on coal gangue coarse-grained subgrade filler (CGSF) under uniaxial compression conditions, and the relationships between load and displacement, crushing strength, failure pattern, and gradation after crushing were analyzed. A new visual analysis method for the crushing patterns of particles was provided through image analysis, and a new gradation equation based on the traditional fractal model was proposed to describe the crushed particles. The results indicate that as the particles are gradually compressed the sharp corners of particles are gradually crushed and fall off, causing the relationship curve between load and displacement to fluctuate and grow, and particle splitting failure leads to the approximately linear growth curve. Moreover, the distribution of particle crushing strength for coal gangue is between 3.02 and 11.11 MPa, and the crushing probability and the applied load well satisfy the Weibull distribution function. Furthermore, as the particle size decreases, the shapes of crushed coal gangue particles are block, flaky, acicular, and powder, and the particles with a size greater than 5 mm are mainly flaky. In addition, comparative analysis shows that the new gradation equation can better describe the gradation of coal gangue fragments after crushing. Full article

There are some limitations in the application of tuff powder as a supplementary cementitious material (SCM). Exploring its feasibility in new fields will consume a large amount of silica-alumina mine solid wastes. This study has investigated the mechanical properties and mechanism in contact-hardening of tuff powder with a method of compression molding. The compressive strength of specimens was tested, and the X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and Mercury intrusion porosimetry (MIP) methods were used to reveal the mechanism of contact-hardening of tuff powder from a micro-perspective. The results indicated that the compressive strength of specimens was higher when activated by sodium hydroxide compared to calcium hydroxide. Compared to calcium hydroxide, the compressive strength of TFS20 and TFF20 activated by sodium hydroxide was improved by 20% and 23%, respectively. The hydration degree of tuff powder was very low, with a water–cement ratio (w/c) of 0.15, while the hydration degree of coal gangue powder was higher. The results of TGA and SEM indicated that the sodium hydroxide had a better activating effect on slag and fly ash. Therefore, more C-S-H gels were generated in those samples activated by sodium hydroxide. Furthermore, the structure of samples was more compacted, and there was a reduction of porosity by 10% and 11% for TFS20 and TFF20, respectively, especially the proportion of harmful pores. Full article

In this paper, a new preparation technology is developed to make high-alumina coal gangue (HACG) auxiliary cementitious admixture by calcining HACG–Ca(OH)₂ (CH) mixture. HACG powders mixed with 20 wt.% CH were calcined within a temperature range of 600–900 °C, and the thermal transformation and mineral phase formation were analyzed. The hydration reaction between activated HACG–CH mixture and cement was also investigated. The results showed that HACG experienced a conventional transformation from kaolinite to metakaolin at 600 °C and finally to mullite at 900 °C, whereas CH underwent an unexpected transformation process from CH to CaO, then to CaCO₃, and finally to CaO again. These substances’ states were associated with the dehydroxylation of CH, the chemical reaction between CaO and CO₂ generating from the combustion of carbon in HACG, and the decomposition of CaCO₃, respectively. It is the formation of a large amount of CaO above 800 °C that favors the formation of hydratable products containing Al₂O₃ in the calcining process and C-A-H gel in the hydration process. The mechanical properties of HACG–cement mortar specimens were measured, from which the optimal calcination temperature of 850 °C was determined. As compared with pure cement mortar specimens, the maximum 28-d flexural and compressive strengths of HACG–cement mortar specimens increased by 5.4% and 38.2%, respectively. Full article

Coal gangue is a solid waste with low carbon content discharged during the course of the coal mining process. The resource utilization of coal gangue could solve environmental problems caused by its excessive production, such as soil contamination and land occupation. This study proposed to produce high-strength thermal insulation bricks using coal gangue as the primary material and three other mineral powders as auxiliary materials, including K-feldspar, CaCO₃ and fly ash. A systematic analysis was conducted to explore the optimum raw material addition ratio and optimum sintering temperature; then, the intrinsic structure of thermal insulation bricks and their sintering formation mechanisms were revealed. The results showed that the optimal ratios of coal gangue, K-feldspar, CaCO₃ and fly ash were 65 wt%, 15 wt%, 10 wt% and 10 wt%, respectively; the compressive strength of the thermal insulation brick produced under this ratio was 22.5 MPa; thermal conductivity was 0.39 W m⁻¹ k⁻¹. During sintering processes, mineral powders sufficiently fused to form a skeleton, and the CO₂ derived from CaCO₃ formed pores. The optimum sintering temperature was 1150 °C, because at this temperature, K-feldspar had the best effect in promoting the conversion of CaCO₃ to Ca-feldspar. The high level of the relative crystallinity of Ca-feldspar (about 76.0%) helped raise the Si–O network’s polymerization degree (NBO/T = 1.24), finally raising the compressive strength of thermal insulation bricks. The innovative method of using coal gangue to make thermal insulation bricks not only solved the environmental pollution caused by coal gangue but also provided excellent construction materials with high practical application value. Full article

In this study, the research aim is to enhance the activity index of activated coal gangue and study its activation mechanism. The activation process of coal gangue was optimized through orthogonal tests, and the Back-Propagation (BP) neural network model was improved using a genetic algorithm. With the effects of grinding duration, calcination temperature, and calcination duration, the morphological changes and phase transformation processes of coal gangue were studied at the micro and meso levels to clarify the activation mechanism. The results indicated that the effect of calcination temperature on the strength activity index of coal gangue was most significant, followed by grinding duration and calcination duration. The potential activity of coal gangue can be effectively stimulated through mechanical and thermal activation, and the content of potential active minerals in coal gangue powders was also increased. The activation process of coal gangue for the optimal scheme was obtained as grinding at 76 min first and thermal treatment at 54 min at 749 °C. As the thermal activation under 950 °C, some unstable external hydroxyls, and internal hydroxyls in kaolinite from coal gangue were removed, the Al^Ⅵ-O octahedron was destroyed, and kaolinite was transformed into spatially disordered metakaolinite with very high activity. Full article

Because of their excellent properties, glass-ceramics have been widely developed and applied in many fields, and there are many potential application values to be disseminated. The preparation of glass-ceramics from industrial slag and metallurgical waste provides a new way for the comprehensive utilization of solid waste. Coal gangue is the largest of all kinds of industrial waste slag, while iron tailings and high-carbon ferrochrome slag also occupy a large proportion of China’s industrial solid waste. With cheap industrial solid waste as the main raw material, the production of high-value-added glass-ceramics can reduce pollution, protect the ecological environment, and have good economic and social benefits. Cordierite glass-ceramics were prepared using the sintering method with coal gangue, iron tailings, and high-carbon ferrochrome slag as the main raw materials. Meanwhile, an iron silicon alloy containing chromium was obtained. The heat treatment system of basic glass was determined by differential scanning calorimetry (DSC), and the sintered product was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). An orthogonal test was used to analyze the effects of the mass of basic glass powder, molding pressure, and holding time on the grain size and crystallinity of the samples. The hardness, acid and alkali resistance, density, and water absorption of the sintered products were determined. The results show that the main crystal phase of the prepared glass-ceramics is cordierite. The optimal combination for the green body is “basic glass powder mass 6 g, molding pressure 35 MPa, holding time 10 min”. The properties of glass-ceramics are good. At the crystallization temperature of 970 °C, the Vickers hardness is up to 866 HV, and the bulk density is up to 2.99 g/cm³. This study may provide a useful reference for the treatment of industrial solid waste. Full article