Gangue Concrete Research Articles

Study on the Effect of Basalt Fiber Content and Length on Mechanical Properties and Durability of Coal Gangue Concrete

The massive accumulation of coal gangue not only causes a waste of resources but also brings serious environmental pollution problems. To promote the utilization of coal gangue resources, mitigate environmental pollution from coal gangue, and address the shortage of natural aggregates, this study investigates the use of coal gangue to replace coarse aggregate at a 40% replacement rate to prepare coal gangue concrete (CGC). The current research on the modification of gangue concrete by BF has been less often compared with the research on the effect of basalt fiber (BF) on the properties of ordinary concrete, so in this study, BF with different admixtures and lengths were added into CGC. Additionally, basalt fibers (BFs) of varying amounts and lengths were incorporated into CGC. The study explored the effects of BF on the tensile strength, splitting tensile strength, and flexural strength of CGC. It was found that the mechanical properties of CGC improved significantly when the BF dosage was 0.10–0.15% and the length was 18 mm. This is evidenced by an increase in the compressive strength of 3.94–5.11%, split tensile strength of 11.20–16.18%, and flexural strength of 8.23–12.97%. BF was able to refine pore space, prevent crack development, and bridge cracks in CGC. To further investigate the effect of BF on the long-term service performance of CGC, the effects of BF on the appearance, quality, and compressive strength of CGC in sulfate and freeze–thaw environments were examined. The results indicated that a BF dosage of 0.10–0.15% significantly enhanced the sulfate erosion resistance and freeze–thaw resistance of CGC. This is shown by a 36.76–46.90% reduction in the rate of loss of compressive strength of CGC under the freeze–thaw cycling and a 6.21–8.50% increase in the corrosion resistance factor of CGC under a sulfate attack. BF improved the pore structure and reduced seepage channels, thereby enhancing the durability of CGC.

Study on the properties of recycled concrete mixed with coal gangue: Mechanics, workability and microstructure

Coal gangue is a by-product in the process of coal mining. Calcined coal gangue powder and coal gangue aggregate are used to prepare concrete, which can not only enhance the utilization rate of coal gangue, but also improve the performance of coal gangue concrete. In this study, calcined coal gangue powder (CCGP) was employed as an auxiliary cementation material, and coal gangue was employed as coarse concrete aggregate (CCA). Different mix proportions were designed to prepare 180 concrete specimens, and slump, cube compressive strength, splitting tensile strength and SEM test were carried out, respectively. The results show that after standing for 120min, the slump of CP0CA0 group is 53 mm, while the slump of CP30CA0 group is only 48 mm. CCGP can reduce the slump loss of concrete over time. The incorporation of CCGP into coal gangue concrete (CGC) can improve the late strength of concrete. When the substitution rate of CCA is constant, the CGC whose substitution rate of CCGP is 20 % will have the best mechanical properties: the compressive strength values are 49.67 MPa, 39.22 MPa and 27.35 MPa; the splitting tensile strength values are 2.92 MPa, 2.59 MPa and 1.92 MPa. In addition, how CCGP affects the mechanical properties of CGC was analyzed from the microscopic level in this paper. Through the regression analysis of the test data, the conversion relationship between the compressive strength and the splitting tensile strength of the concrete mixed with CCGP and CCA was obtained, which can be used to predict the splitting tensile strength. The results of this study can provide a new research idea for the efficient utilization of coal gangue.

Synergistic action and effect mechanism of coal gangue powder and red mud on the properties of concretes

Red mud and coal gangue powder were employed as substitutes for cement to prepare red mud concrete, coal gangue concrete, and red mud-coal gangue concrete. The effects of red mud and coal gangue powder on the physical properties, workability, and mechanical properties of concretes were evaluated, and the hydration reaction mechanisms were elucidated through microanalysis. Furthermore, the reaction process was investigated through thermogravimetric analysis. The results indicated that the individual addition of red mud and coal gangue powder had negative effect on the strength, workability, and porosity of concretes. However, the combination of red mud and coal gangue powder significantly improved the strength and porosity of the concrete compared to red mud concrete and coal gangue concrete. The red mud-coal gangue concrete with 15 % red mud and 15 % coal gangue powder had lower porosity, and comparable compressive strength with the cement concrete. The microscopic results and thermogravimetric analyses indicated that the synergistic effect of red mud and coal gangue led to the improvement of the strength of red mud-coal gangue concrete. The red mud exhibited the promotion effect on the hydration of coal gangue powder to generate new C-S-H, filling the pores. The denser structure in the red mud-coal gangue concrete was formed, thereby improving the pore space and mechanical properties of the concretes.

Experimental study on constitutive relation of coal gangue coarse aggregate concrete under uniaxial compression

As an efficient method for utilizing coal gangue (CG), concrete incorporating coal gangue as coarse aggregate has significantly reduced the reliance on natural aggregates, offering substantial environmental and economic benefits. In this study, coal gangue concrete was prepared with coal gangue replacement rates of 0, 20, 40, 60, 80, and 100%, and mechanical tests under unconfined compression were conducted to evaluate the stress-strain behavior and failure mechanism of coal gangue coarse aggregate concrete (CGC). Utilizing scanning electron microscope (SEM) microscopic characterization, the microscopic failure mechanism of CGC was further elucidated. With increased coal gangue replacement, the CGC's uniaxial compression failure mode shifts from shear to longitudinal splitting failure. The slope, peak stress and elastic modulus of the stress–strain curve's rising section are negatively correlated with the coal gangue content, while the falling section's slope, peak strain and ultimate strain are positively correlated. Next, building upon the classical constitutive model, we adjust the constitutive parameters utilizing the uniaxial compressive strength and coal gangue content. Finally, we introduce a predictive model for the CGC's constitutive compressive behavior across various content levels. There is a notably high agreement between the model and experimental data.

Study on Mechanical Properties and Constitutive Relationship of Steel Fiber-Reinforced Coal Gangue Concrete after High Temperature

Study on Mechanical Properties and Constitutive Relationship of Steel Fiber-Reinforced Coal Gangue Concrete after High Temperature

Behavior of steel fiber-reinforced coal gangue concrete beams under impact load

In order to promote the use of new sustainable steel fibers (SF) reinforced coal gangue aggregates (CGA) concrete, impact tests were performed in this paper. The impact resistance of steel fiber-reinforced coal gangue concrete was investigated using a self-developed drop-weight facility. The test variables were the CGA replacement rate (0 %, 50 %, and 100 %), the SF volume content (0 %, 0.75 %, and 1.5 %), and the drop height of the drop-weight (0.5 m and 1.0 m). Using 15 kg of hard steel as a drop-weight, the drop-weight impact test was performed on steel fiber-reinforced coal gangue concrete beams with a span of 300 mm; the damage pattern, impact reaction force-time, displacement-time relationships, and energy absorbed by steel fiber-reinforced coal gangue concrete beams were studied. The test shows that, compared with natural aggregate, CGA reduces concrete's static mechanical properties and impact resistance, and adding SF improves the static mechanical properties and impact resistance of coal gangue concrete. As the CGA replacement rate increased from 0 % to 50 % and 100 %, the reaction force of impact of the specimens decreased by 2.54 %− 6.06 % and 3.69 %− 12.33 %. The SF volume content was increased from 0 % to 0.75 % and 1.5 %, and the reaction force of impact of the specimens was increased by 23.05 %− 32.34 % and 72.27 %− 81.84 %, respectively. The impact resistance of steel fiber-reinforced concrete beams under impact loading was investigated numerically using a nonlinear explicit finite element model in LS-DYNA. The Finite Element results were validated with experimental results. Based on the validated finite element model, a parametric study was carried out to investigate the effects of coal gangue replacement rate, steel fiber volume content, and drop height of the drop weight on the behavior of the beams. This study might provide a basis for the future engineering project applications of steel fiber-reinforced coal gangue concrete under impact conditions.

Experimental study on the bond-slip behavior of steel tube-coal gangue concrete

This study investigated the bond-slip behavior at the interface between steel tubes and coal gangue concrete, considering the coal gangue coarse aggregate replacement rate, the strength grade of coal gangue concrete, and the bond length as variable parameters. Eleven groups of push out tests were conducted on steel tube coal gangue concrete specimens. The bond slip curve and the longitudinal strain distribution curve of the steel tubes were obtained, and the effects of these parameters on bond strength were analyzed. The results showed that the load-slip curves at both the loading and free ends of the specimens were similar, with slip occurring earlier at the loading end. The regularity of the test curves in repeated experiments indicated that interfacial bond stress was primarily determined by friction in the later stages. The longitudinal strain of steel tubes was approximately exponentially distributed along their length. The interfacial bond strength increased with the increase of coal gangue aggregate replacement rate and was more pronounced in specimens with higher strength coal gangue concrete. Longer bond lengths resulted in greater bond failure loads, with a lower rate of increase in higher strength coal gangue concrete specimens compared to those with lower strength. Based on the three stage bond stress-slip relationship for steel tube-concrete, a bond-slip constitutive model for steel tube-coal gangue concrete was established. This provided a reference for mechanical analysis and interface performance design of steel tube-coal gangue concrete.

Enhancing Fatigue Performance of Coal Gangue Concrete (CGC) through Polypropylene Fiber Modification: Experimental Evaluation.

Coal gangue is a byproduct of coal mining and processing, and according to incomplete statistics, China has amassed a substantial coal gangue stockpile exceeding 2600 large mountains, which poses a serious threat to the ecological environment. Utilizing gangue as a coarse aggregate to produce gangue concrete (GC) presents a promising avenue for addressing the disposal of coal gangue; however, gangue concrete presents several challenges that need to be tackled, such as low strength and poor resistance to repeated loads. In this study, polypropylene fibers (PPFs) were incorporated into gangue concrete to enhance its utilization rate. Uniaxial compressive and repeated loading experiments were then conducted to investigate the uniaxial strength and fatigue properties of polypropylene fiber-reinforced gangue concrete (PGC) with varying gangue substitution rates (20%, 40%, and 60%) and different polypropylene fiber admixtures (0, 0.1%, 0.2%, and 0.3%). The findings indicate that incorporating gangue at a substitution rate of 40% could notably enhance the uniaxial compressive strength of PGC, resulting in a maximum increase of 19.4%. In the repeated loading experiments, the ductility of PGC was enhanced with the incorporation of PPFs, resulting in a reduction of 33.76% in the damage factor and 19.42% in residual strain for PGC-40-0.2 compared to PGC-40-0. A PPF content of 0.2% was found to be optimal for enhancing the fatigue performance of PGC. Scanning electron microscope (SEM) testing proved the improvement effect of polypropylene fiber on gangue concrete from a microscopic perspective. This study provides crucial experimental data and a theoretical foundation for the utilization of gangue concrete in complex stress environments.

Experimental Study on the Mechanical Properties of Disposable Mask Waste-Reinforced Gangue Concrete.

This paper is grounded on the following information: (1) Disposable masks primarily consist of polypropylene fiber, which exhibits excellent flexibility. (2) China has extensive coal gangue deposits that pose a significant environmental hazard. (3) Coal gangue concrete exhibits greater fragility compared to regular concrete and demonstrates reduced resistance to deformation. With the consideration of environmental conservation and resource reutilization, a preliminary concept suggests the conversion of discarded masks into fibers, which can be blended with coal gangue concrete to enhance its mechanical characteristics. In this paper, the stress-strain law of different mask fiber-doped coal gangue concrete (DMGC) under uniaxial compression is studied when the matrix strength is C20 and C30, and the effect of mask fiber content on the mechanical behavior and energy conversion relationship of coal gangue concrete is analyzed. The experimental results show that when the content of mask fiber is less than 1.5%, the strength, elastic modulus, deformation resistance, and energy dissipation of the concrete increase with mask fiber content. When the amount of mask fiber is more than 1.5%, because the tensile capacity and energy dissipation level of concrete produced by the mask fiber cannot compensate for the compression and deformation resistance of concrete of the same quantity and because excess fiber is difficult to evenly mix in the concrete, there are pore defects in concrete, which decreases the concrete strength due to the increase in mask fiber. Therefore, adding less than 1.5% mask fiber helps to improve the ductility, toughness, impermeability, and oxidation and control the cracking of coal gangue concrete. Based on Weibull theory, a constitutive model of DMGC is established, which fits well with the results of a uniaxial test, providing support for understanding the mechanical law of mask fiber-doped concrete.

Effect of temperature on thermal properties and residual strength of coal gangue concrete

Key factors for assessing the high-temperature resistance of coal gangue concrete are high-temperature residual strength and thermal properties. The high-temperature residual strength, high-temperature thermal conductivity, high-temperature specific heat capacity, and high-temperature density of concrete with various coal gangue coarse aggregate replacement ratios were tested using experimental methods in this paper to study the high-temperature resistance of coal gangue concrete. Thermal density and high-temperature residual strength tests took into account influencing factors like the water-cement ratio (0.50, 0.45, 0.40), aggregate replacement ratio (0, 25 %, 50 %, 75 %, 100 %), and temperature variation (room temperature, 200 °C，300 °C，400 °C，500 °C，600 °C，700 °C，800 °C), while thermal properties tests considered the effects of various coarse aggregate replacement ratios and temperatures. The study showed that when the temperature rises, coal gangue concrete's thermal density falls, mass loss rises, residual strength declines, thermal conductivity rises, and its specific heat capacity fluctuates. At temperatures between 20 °C and 400 °C, concrete's residual strength decreases with an increase in the coal gangue coarse aggregate replacement ratio, while thermal conductivity and specific heat capacity increase. At temperatures between 500 °C and 800 °C, however, concrete's residual strength slightly improves with an increased coal gangue coarse aggregate replacement ratio, while mass loss changes more. The research finally provides the formulae for calculating the high-temperature residual strength and thermal properties of coal gangue concrete based on the test results.

Study on the Modification Effect and Mechanism of a Compound Mineral Additive and Basalt Fiber on Coal Gangue Concrete

Compared with ordinary concrete, coal gangue concrete (CGC) is limited by its poor mechanical properties and frost resistance, which seriously restricts its wide application in cold regions. In order to improve the resource utilization rate of coal gangue, this paper takes advantage of the ‘overlapping effect’, ‘micro-aggregate filling effect’ and ‘volcanic ash effect’ of fly ash (FA) and silica fume (SF) and the anti-cracking effect of basalt fiber (BF) to study their effects on the macro performance of CGC and the micro modification mechanism. Modified CGC was prepared by replacing cement with 20% total mineral additives and adding BF. Taking different fly ash and silica fume incorporation ratios (F/S) and the BF content as variables, the research was carried out from two scales of macro performance and microstructure. The results show that the mechanical properties and frost resistance of CGC can be significantly improved by adding mineral additives and BF, and the modification effect is better with a decrease in F/S. When F/S = 1, the compressive strength, splitting tensile strength and flexural strength of the specimens increased by 13.73%, 8.37% and 4.27%, respectively. After 300 freeze–thaw cycles, the specimen was still not damaged by freezing and thawing. At the same time, keeping F/S = 3 unchanged and changing the BF content, it was found that the optimal content of BF was 0.15 vol% under the combined action of BF, FA and SF. In terms of microstructure, the addition of mineral additives and BF segregates and fills the macropores in the structure, greatly reducing the harmful pores and turning them into harmless and less harmful pores. When F/S = 1, the number of multi-harmful pores decreased by 16.89%, and the number of harmless pores and less harmful pores increased by 9.19%, which greatly optimized the pore structure and pore gradation.

Damage Model of Steel Fiber-Reinforced Coal Gangue Concrete under Freeze-Thaw Cycles Based on Weibull Distribution.

In order to improve the utilization rate of coal gangue and expand the application range of coal gangue concrete (CGC), a certain proportion of steel fiber was added to the concrete, and the freeze-thaw cycles (FTCs) and flexural tests were used to explore the effects of different mass replacement rates of coal gangue (0%, 25%, 50%, 75%, and 100%) and different proportions of the volumetric blending of the steel fiber (0%, 0.8%, 1.0%, and 1.2%) on the frost resistance of steel fiber-reinforced CGC (SCGC). The governing laws of mass loss rate, relative dynamic elastic modulus and load-midspan deflection curve were obtained on the base of the analysis of testing results. The damage mechanisms of the SCGC under the FTCs were analyzed using the results of scanning electron microscopy (SEM). Based on the Lemaitre's strain equivalence principle and Krajcinovic's vector damage theory, a damage evolution model of the SCGC under the FTCs was established by introducing the damage variable of the SCGC satisfying Weibull distribution. The results show an increasing mass loss rate of the SCGC and a decreasing relative dynamic elastic modulus with an increasing mass replacement rate of coal gangue. The proper content of the steel fiber can reduce the mass loss rate of concrete by 10~40% and the relative loss rate of dynamic elastic modulus of concrete by 2~8%, thus significantly improving the ductility and toughness of the concrete. The established damage evolution model is well validated by the experimental results, which further help to improve the modelling accuracy. This study provides key experimental data and a theoretical basis for a wider range of proper utilization of coal gangue in cold regions.

Mechanical properties and microscopic characteristics of steel fiber coal gangue concrete

Incorporation of coal gangue in the concrete mixes can realize utilization of the solid waste and reduce extraction/use of natural aggregates. To improve the mechanical properties of coal gangue concrete, this paper studies use of steel fibre together with coal gangue coarse aggregate, coal gangue fine aggregate/sand in various concrete mixes. The effect of volume dosages of steel fibre and different levels of replacing nature coarse aggregate and river sand with coal gangue aggregates on concrete compressive strength was first investigated. Then, a design of experiment using orthogonal test was adopted to study concrete mixes with 3 factors, namely, coal gangue coarse aggregate, coal gangue sand and steel fibre, and each at 3 levels. Through multidimensional statistical data analysis of the test results, the primary and secondary factors and the optimal composition of the steel fibre reinforced coal gangue concrete were identified, and a grey prediction model for compressive strength of the concrete mixes established. The microstructural characteristics and failure mechanism of steel fiber reinforced coal gangue concrete was also studied and discussed.

Emergy-accounting-based comparison of carbon emissions of solid waste recycled concrete

The carbon emission emergy factor (Em-CEF) model is applied to evaluate the carbon emissions associated with the traditional concrete production method, fly ash concrete production method, coal gangue concrete production method, and recycled aggregate concrete production method in the complete lifecycle. The highest emission reduction can be achieved when solid industrial waste is used to replace part of the traditional raw materials, and the processing and treatment of industrial waste are simplified. Among the four production methods, gangue concrete production corresponds to the highest emission reduction. When solid waste recycled concrete is applied to reduce carbon emissions, coal gangue concrete can be prioritized.

Degradation Mechanism of Coal Gangue Concrete Suffering from Sulfate Attack in the Mine Environment.

Recycling coal gangue as aggregate to produce concrete in situ is the most effective way to solve the problem of deposited coal gangue in mines. Nevertheless, the mine environment underground is rich in sulfate ions, posing a threat to the durability of coal gangue concrete (CGC). Hence, the degradation process of sulfate-attacked CGC is investigated. A series of tests is performed to evaluate its variation law of mass, dynamic elastic modulus, compressive strength and sulfate ion distribution. Meanwhile, the microstructure and phases of sulfate-attacked CGC are identified by scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. The results indicate that the residual compressive strength ratio of CGC is higher than that of normal concrete after a 240 d sulfate attack, implying a superior sulfate resistance for CGC. Additionally, the higher the sulfate concentration, the more severe the degradation. Except for the secondary hydration of CGC itself, the diffused sulfate ions also react with Ca(OH)2, forming gypsum and ettringite; this plays a positive role in filling the pores at the early stage, whereas, at the later stage, the generated micro-cracks are detrimental to the performance of CGC. In particular, the proposed sulfate corrosion model elucidates the degradation mechanism of CGC exposed to a sulfate-rich environment.

Experimental study on bond performance between deformed steel bar and coal gangue concrete

AbstractCoal gangue concrete (CGC), a great low cost and environment‐friendly material, is considered to be the most effective substitute for normal concrete. The bond performance of steel bar embedded in CGC determines the feasibility of using CGC as structure material. So, this study presents an experimental program to investigate the bond strength of steel bar embedded in CGC compared to the one in normal‐aggregate concrete. The experimental program contains 75 specimens that are tested using the pull‐out test. In this study, coal gangue coarse aggregate replacement ratios (0%, 25%, 50%, 75%, and 100%), water–cement ratio (0.50, 0.45, and 0.40), and rebar diameters (14 mm, 16 mm, and 18 mm) were considered to analyze the variation law of bond strength. The test results show that the bond strength increased slightly with the decrease of water–cement ratio. The bond strength decreased slightly with the increase the aggregate replacement ratio if the replacement ratio was less than 50%. In contrast, the bond strength decreased significantly when the aggregate replacement ratio was more than 50%. In addition, the bond strength increases first and then reduces with increasing of bar diameters. Lastly, a new model of predicting the bond strength between the deformed steel bar and coal gangue concrete was proposed in this study because the widely used prediction models for the bond strength were not suitable for the coal gangue concrete.

Mechanical Properties and Drying Shrinkage of Alkali-Activated Coal Gangue Concrete

The feasibility of composite-activated coal gangue (CACG) as the primary cementitious material for concrete was experimentally studied in this paper. The effects of concrete strength grade on slump and slump flow, compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, and drying shrinkage of alkali-activated coal gangue concrete (AACGC) were experimentally investigated. Experimental results indicated that the slump and slump flow of the AACGC were smaller than that of ordinary Portland cement concrete (OPCC). The mechanical properties of the AACGC were superior to those of the OPCC. The compressive strength, splitting tensile strength, axial compressive strength, and elastic modulus of the AACGC were 1.17 times, 1.04 times, 1.47 times, and 1.04 times those of the OPCC, respectively. With the increase in concrete strength grade, the mechanical properties of the AACGC have gradually increased. The difference in failure modes of axial compressive strength between the AACGC and OPCC was analyzed. Moreover, the empirical formulas of the elastic modulus and compressive strength for the OPCC in various regions codes were summarized, and found that the empirical formula in GB 50010-2002 code and EN 1922 Eurocode 2 was also applicable to the AACGC. Finally, the mass-loss rate and drying shrinkage for the AACGC at different concrete strength grades were systematically analyzed, and a hyperbolic prediction model was proposed to reflect the drying shrinkage behavior of the AACGC.

Using Chinese Coal Gangue as an Ecological Aggregate and Its Modification: A Review.

Coal gangue is a kind of industrial solid waste with serious ecological and environmental implications. Producing concrete with coal gangue aggregate is one of the green sustainable development requirements. This paper reviews the properties and preparation methods of Chinese gangue aggregate, studies the influence of gangue aggregate on concrete properties and the prediction model of gangue concrete, and summarizes the influence of modified materials on gangue concrete. The studies analyzed in this review show that different treatments influence the performance of coal gangue aggregate concrete. With the increase in the replacement ratio of coal gangue aggregate in concrete, the concrete workability and mechanical performance are reduced. Furthermore, the pore structure changes lead to decreased porosity, greatly affecting the durability. Coal gangue is not recommended for producing high-grade concretes. Nevertheless, pore structure can be improved by adding mineral admixtures, fibers, and admixtures to the coal gangue concrete. Hence, the working properties, mechanical properties, and durability of the concrete can be improved effectively, ensuring that coal gangue concrete meets engineering design requirements. Adding modified materials to coal gangue concrete is a viable future development direction.

Examination of Mixing Proportion in Self-Compacting Gangue-Based Pavement Concrete

In recent years, with the rapid development of the coal-mining industry, the output of gangue has increased at a faster pace, while its utilization remains relatively low. The accumulation of a large amount of gangue has brought about a large environmental problem. In order to improve the utilization rate of waste gangue, and to solve the secondary environmental problems caused by gangue pollution, this paper conducted research on an economic and environmentally friendly gangue-based self-compacting concrete. This study designed aggregate industrial-analysis experiments to analyze the moisture content of the gangue and limestone, finding that the moisture content of gangue is 39% higher than that of limestone. By orthogonal experimental methods, the study investigated the fluidity, compressive strength, splitting strength and abrasion resistance of self-compacting gangue concrete. It was concluded that the optimal replacement rate of gangue for coarse aggregate is around 30%, the optimal replacement rate of fly ash for cement is around 30%, the optimal addition of polycarboxylate superplasticizer is 0.5% of the mass of cementitious materials, and the optimal rate of shear steel fibers is around 1% of the concrete capacity. In addition, this paper investigated the interfacial transition zone (ITZ) of the aggregate–cement slurry and found that the ITZ of gangue aggregate and cement mortar is more likely to generate AFT crystals, which will contribute more to the improvement of the strength of concrete in the early stage. In addition, a field-effect analysis was carried out in this study, and it found that gangue-based self-compacting concrete, as an environmentally friendly material, can basically meet the design requirements of C30 paving concrete.

Deterioration mechanism of coal gangue concrete under the coupling action of bending load and freeze–thaw

Coal gangue, as a solid waste produced in the process of coal mining, has caused great harm to the environment and society. It is the most practical means to make concrete as coarse aggregate. In practical engineering, concrete materials are often subjected to the combined action of external load and environmental factors. Simply considering the freeze–thaw effect cannot reflect the deterioration characteristics of coal gangue concrete, so that the popularization and application of coal gangue cannot be realized. Based on this, through bending load and freeze–thaw coupling test (stress level 0, 0.2, 0.4, 0.6, 0.8), the mass loss rate, relative dynamic elastic modulus, damage layer thickness, and compressive strength of coal gangue concrete with a replacement rate of 40% were analyzed. The degradation characteristics of pore structure and interface transition zone of coal gangue concrete were studied by nuclear magnetic resonance test and microhardness test. The effects of different stress levels on pore size distribution, pore grade ratio, pore fluid characteristics, and interface zone characteristics were analyzed. The results show that the larger the bending stress ratio is, the faster the degradation of compressive strength and relative dynamic elastic modulus of coal gangue concrete is, the faster the thickness of damage layer increases, the larger the proportion of large pores in the specimen is, and the pore connectivity is enhanced. In addition, the interface area between coal gangue aggregate and mortar is the weak position of coal gangue concrete, and its thickness and microhardness are widened and decreased with the increase of stress level. The deterioration of the interface area makes the specimen close to failure.