Materials

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17 pages, 23566 KiB

Open AccessArticle

Mechanical Behavior and Crack Evolution of Goaf Surrounding Rock with Different Roof-Contacted Filling Rates

by Jie Wang, Kaifei Huang, Jianxin Fu and Weidong Song

Materials 2023, 16(12), 4435; https://doi.org/10.3390/ma16124435 - 16 Jun 2023

Viewed by 575

The goaf formed by mining is filled and treated, which greatly improves the safety and stability of the surrounding rock. During the filling process, the roof-contacted filling rates (RCFR) of goaf were closely related to the stability control of the surrounding rock. The [...] Read more.

The goaf formed by mining is filled and treated, which greatly improves the safety and stability of the surrounding rock. During the filling process, the roof-contacted filling rates (RCFR) of goaf were closely related to the stability control of the surrounding rock. The influence of the roof-contacted filling rate on the mechanical characteristics and crack propagation of the goaf surrounding rock (GSR) has been studied. Biaxial compression experiments and numerical simulation experiments were conducted on samples under different operating conditions. The results were as follows: (1) The peak stress, peak strain, and elastic modulus of the GSR are closely related to the RCFR and the goaf size; they increase with the increase of the RCFR, and decrease with the increase of the goaf size; (2) In the initial loading stage, a small number of cracks are generated, and the acoustic emission ringing count increases slowly. The mid-loading stage is the crack initiation and rapid expansion, and the cumulative ring count curve shows a “stepwise” growth. In the later loading stage, cracks continue to propagate and form macroscopic fractures, but the number of rings significantly decreases; (3) Shear cracks are prone to occur in the rock part of the GSR; tensile cracks are prone to occur in the backfill; and the crack propagation speed in the rock is faster than in the backfill. Stress concentration is the direct cause of GSR failure. The maximum concentrated stress of rock mass and backfill is 1~2.5 times and 0.17~0.7 times of the peak stress of the GSR, respectively. Full article

(This article belongs to the Special Issue Mechanical and Modeling of Composite Materials)

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15 pages, 5363 KiB

Open AccessArticle

The Failure Mechanical Properties of Cemented Paste Backfill with Recycled Rubber

by Baogui Yang, Xiaolong Wang, Chengjin Gu, Faguang Yang, Hao Liu, Junyu Jin and Yibo Zhou

Materials 2023, 16(9), 3302; https://doi.org/10.3390/ma16093302 - 22 Apr 2023

Cited by 1 | Viewed by 1123

Abstract

Understanding the mechanical properties and failure process of cemented paste backfill with recycled rubber (RCPB) is the foundation of backfill design in underground mining. In this study, physical and mechanical tests were conducted on RCPB to obtain its mechanical property parameters, such as [...] Read more.

Understanding the mechanical properties and failure process of cemented paste backfill with recycled rubber (RCPB) is the foundation of backfill design in underground mining. In this study, physical and mechanical tests were conducted on RCPB to obtain its mechanical property parameters, such as its uniaxial compressive strength (UCS), toughness, and peak strain. The influence of the rubber dosage on the mechanical properties of RCPB was also analyzed. In addition, the deformation behavior, fracture development, and failure process of RCPB with different rubber contents were observed using the digital image correlation (DIC) technique. The experimental results suggested that, although the UCS of RCPB is reduced as more rubber is added, its toughness and ability to absorb energy is increased. Moreover, the impact resistance of RCPB is improved by this increased toughness. With the increase in the rubber content, the deformation corresponding to the plastic yield stage of RCPB increased, which resulted in better ductility and improved impact resistance. The failure of the RCPB specimens mainly showed an “X” shape. The results of this study help us to better understand the mechanical behavior of RCPB after backfilling underground. Full article

(This article belongs to the Special Issue Mechanical and Modeling of Composite Materials)

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17 pages, 3980 KiB

Open AccessArticle

Mechanical and Hydration Characteristics of Stabilized Gold Mine Tailings Using a Sustainable Industrial Waste-Based Binder

by Zhenkai Pan, Shaohua Hu, Chao Zhang, Tong Zhou, Guowei Hua, Yuan Li and Xiaolin Lv

Materials 2023, 16(2), 634; https://doi.org/10.3390/ma16020634 - 9 Jan 2023

Viewed by 1416

Abstract

Sustainable resource utilization of tailings is a long-term challenge. Therefore, a novel waste-based binder is proposed in this study to stabilize/solidify gold mine tailings (GMTs). This binder is composed of fly ash (FA), ground blast furnace slag (GBFS), and metakaolin (MK) activated with [...] Read more.

Sustainable resource utilization of tailings is a long-term challenge. Therefore, a novel waste-based binder is proposed in this study to stabilize/solidify gold mine tailings (GMTs). This binder is composed of fly ash (FA), ground blast furnace slag (GBFS), and metakaolin (MK) activated with mixed calcium carbide residue (CCR) as well as pure reagent grade chemical, sodium hydroxide (SH, NaOH), and plaster gypsum (PG, CaSO₄·2H₂O). The mechanical properties and hydration of stabilized tailings with curing period were investigated. Tests included triaxial compression test and nitrogen adsorption to evaluate the strength of the stabilized tailings and microstructure. The results show that the addition of the waste-based binder yields significant improvement in shear strength. Strain softening occurred for all cured samples, and a local shear band can be observed in all failed stabilized samples. Based on the relationship between strength and curing period, it can be speculated that the hydration reaction of the sample ends after around 40 days of curing. A bimodal pore-size distribution was observed in all solidified/stabilized samples. FTIR and ²⁷Al MAS-NMR were used to analyze hydration products. The strength improvement of stabilized tailings was mainly attributed to the formation of ettringite and C–S–H gels after various polymerization reactions. These new hydrates bind tailings particles and fill the pores to form a more stable structure, which supplied superior mechanical properties. This paper can provide a theoretical basis for exploring the application of the industrial waste-based binder to modify the mechanical properties of gold tailings. Full article

(This article belongs to the Special Issue Mechanical and Modeling of Composite Materials)

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15 pages, 18103 KiB

Open AccessArticle

Fracture Process Analysis and Acoustic Emission Response of Cemented Tailings Backfill with Different Sizes under Uniaxial Compression

by Kui Zhao, Zhouchao Liu, Peng Zeng, Cong Gong and Yanda Li

Materials 2022, 15(22), 8038; https://doi.org/10.3390/ma15228038 - 14 Nov 2022

Cited by 6 | Viewed by 934

Abstract

To investigate the effect of dimensional changes on the mechanical properties of cemented tailings backfill (CTB), uniaxial compression tests are performed on square CTBs of four different sizes. Combining digital image correlation (DIC) and acoustic emission (AE) methods, the fracture process and AE [...] Read more.

To investigate the effect of dimensional changes on the mechanical properties of cemented tailings backfill (CTB), uniaxial compression tests are performed on square CTBs of four different sizes. Combining digital image correlation (DIC) and acoustic emission (AE) methods, the fracture process and AE behavior characteristics of backfills with different sizes are analyzed. The results show that as the backfill size increases, its uniaxial compressive strength decreases, and its strength stabilizes gradually when it measures 100 mm. Under uniaxial compression loading, surface cracks on the smaller specimens evolve rapidly and aggressively, with no significant shedding area, whereas the larger specimens show plastic failure. The cracks expand and penetrate gradually, forming a large shedding area. As the specimen size increases, the backwards trend of the peak value of the ringing count relative to the peak value of the stress becomes increasingly evident. Combining the change law between the r value and the average frequency centroid, the sudden drop point of r value and the lowest value of average frequency centroid can be regarded as the precursor of macroscopic damage. Full article

(This article belongs to the Special Issue Mechanical and Modeling of Composite Materials)

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16 pages, 18278 KiB

Open AccessArticle

Experimental Study of the Damage and Failure Characteristics of the Backfill-Surrounding Rock Contact Zone

by Guang Li, Yang Wan, Jie Guo, Fengshan Ma, Haijun Zhao and Yanfang Wu

Materials 2022, 15(19), 6810; https://doi.org/10.3390/ma15196810 - 30 Sep 2022

Cited by 1 | Viewed by 1303

Abstract

Due to obvious differences in the properties of the filling body and surrounding rock, deformation always develops near the contact zone. Thus, determining the damage and failure characteristics of the contact zone between the backfill and surrounding rock is a precondition for safe [...] Read more.

Due to obvious differences in the properties of the filling body and surrounding rock, deformation always develops near the contact zone. Thus, determining the damage and failure characteristics of the contact zone between the backfill and surrounding rock is a precondition for safe production in mines. Taking Jinchuan mine as study area, the backfill-surrounding rock contact zones are divided into three models according to their different geometric shapes, namely, a linear model, embedded model, and multiple broken line model. A combined numerical simulation and physical model test method was adopted in this study. The research results show that the damage in the linear model begins at the seam, the failure is mainly concentrated in the filling body, and shear failure is dominant. The damage in the embedded model initially occurs around the inflection points, while the damage in the multiple broken line model initially occurs at the seams, and cracks always appear on the vertical contact surface first. Among the three contact models, the stability increases as follows: embedded > multiple broken line > linear. Moreover, the filling body enclosed by surrounding rock is the most stable, and the surrounding rock located in the footwall is more stable than the filling body located in the footwall. The conclusions of this study provide a theoretical basis for designing a mining scheme for Jinchuan mine and other mines with similar geological conditions and mining methods, and they provide a reference for studying the mechanical properties and stability of composite materials. Full article

(This article belongs to the Special Issue Mechanical and Modeling of Composite Materials)

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21 pages, 14026 KiB

Open AccessArticle

Study on Multi-Layer Filling Treatment of Extra-Large Goaf and Its Underground Application

by Huazhe Jiao, Wenbo Yang, Huiming Shen, Yingjie Yang and Juanhong Liu

Materials 2022, 15(16), 5680; https://doi.org/10.3390/ma15165680 - 18 Aug 2022

Cited by 3 | Viewed by 1128

Abstract

At present, the many domestic, large mined-out areas caused by single filling ability of the slurry flow state, thin layer flow and hardening after filling in multilayer structure generally need to finish filling for many times, because after a filling experience shows that [...] Read more.

At present, the many domestic, large mined-out areas caused by single filling ability of the slurry flow state, thin layer flow and hardening after filling in multilayer structure generally need to finish filling for many times, because after a filling experience shows that filling body in the last solidification of flow, this leads to a lower one side of the roof, and far distance part of the filling body cannot pick up top. The determination of backfill strength is the key problem of the cemented backfill method, and it is affected by many factors. Therefore, through theoretical calculation, laboratory testing and numerical simulation methods, combined with the field filling process, this paper has verified the flow accumulation and stratification characteristics of stope layered filling slurry. When the slurry concentration is 60–73%, the slope increases exponentially from 2.5° to 8°. It is revealed that the delamination and meshing state are the key factors to determine the overall strength of large-scale stope filling through the testing of particle size distribution in interlayer and flow direction. The reduction effect of the number and Angle of structural weak surface formed by layering and filling on strength is revealed: cement–sand ratio 1:12, concentration 68%, standard curing R28 > 1.81 MPa. The strength reduction coefficient is 61.31% and 92.96% when the number of layers is 1–4. The higher the number of layers, the greater is the reduction coefficient, and when the stratification angle increases by 2, the strength of backfill decreases by 20–30%. The verification of stope filling coring shows that the in situ strength reaches 2.42 MPa, which is 0.61 MPa higher than the standard curing strength, with an increase of 33.7%. When the depth is from 1 m to 5 m, the strength increases from 2.26 MPa to 2.69 MPa, with an increase rate of 18.2%. Finally, through the research and application of the comprehensive technology of mining and filling coordination under the complex goaf group, the residual ore resources of Xianglushan tungsten mine are effectively recovered, the volume of goaf is significantly reduced, and the safety of goaf is improved. Full article

(This article belongs to the Special Issue Mechanical and Modeling of Composite Materials)

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14 pages, 2904 KiB

Open AccessArticle

Micro-Mechanism of Uniaxial Compression Damage of Layered Cemented Backfill in Underground Mine

by Xinming Chen, Haowen Zhang, Yuping Wu, Huazhe Jiao, Liuhua Yang, Qinting Wang and Wenxiang Zhang

Materials 2022, 15(14), 4846; https://doi.org/10.3390/ma15144846 - 12 Jul 2022

Cited by 4 | Viewed by 1139

Abstract

Layering of filling body is common in large-scale filling areas. In this paper, the cement–sand ratio of 1:8 is based on the configuration of 68%, 70%, 72% and 74%; four concentrations; and filling layers of one-, two-, three- and four-layered cemented filling samples. [...] Read more.

Layering of filling body is common in large-scale filling areas. In this paper, the cement–sand ratio of 1:8 is based on the configuration of 68%, 70%, 72% and 74%; four concentrations; and filling layers of one-, two-, three- and four-layered cemented filling samples. Combined with a uniaxial compression test and two-dimensional particle flow software (PFC2D), the mechanical properties and failure modes were explored. The results show that the concentration can strengthen the uniaxial compressive strength of the filling body while increasing the filling times weakens its power; therefore, the constitutive damage model was constructed. It was found that the initial layered damage existed in the layered filling, and the total damage showed an upward trend of first fast and then slow; the main failure modes of one-layer and two-layer backfills showed prominent shear failure characteristics, and the three-layer and four-layer fillings were closer to tensile failure. From the crack generation to the specimen failure, there is a mutual conversion between different energies. Full article

(This article belongs to the Special Issue Mechanical and Modeling of Composite Materials)

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13 pages, 962 KiB

Open AccessArticle

Effects of Different Factors on the Performance of Recycled Aggregate Permeable Pavement Concrete

by Ruidong Wu, Shuning Shi, Yu Shen, Chen Hu, Mengfei Luo, Zichen Gan, Bin Xiao and Zeyu Wang

Materials 2022, 15(13), 4566; https://doi.org/10.3390/ma15134566 - 29 Jun 2022

Cited by 3 | Viewed by 1500

Abstract

Urban construction has produced a large amount of construction waste which has caused huge environmental problems. The sponge city is the development direction of urban construction, and permeable pavement concrete is an important material for sponge city construction. To see the law influencing [...] Read more.

Urban construction has produced a large amount of construction waste which has caused huge environmental problems. The sponge city is the development direction of urban construction, and permeable pavement concrete is an important material for sponge city construction. To see the law influencing different factors on the performance of recycled aggregate permeable pavement concrete, different water binder ratios, recycled aggregate particle gradations, ordinary aggregate substitution rates, and fly ash and admixture contents are designed to prepare permeable concrete. The compressive strength, permeability coefficient, frost resistance, and pore structure of permeable concrete are tested. The results show that when the replacement rate of recycled aggregate is 50%, the 28-d strength of concrete with a 0.25 water binder ratio can reach 28.9 MPa, and the permeability coefficient is 13.26 mm/s. The addition of fly ash will reduce the compressive strength, and the permeability coefficient increases first and then decreases with the increase of the fly ash content. When the mass fraction of fly ash instead of cement is 12%, the 28-d strength is 94.8% of that of the cement group, and the permeability coefficient can reach 14.03 mm/s. A water-reducing agent can obviously improve the workability of permeable concrete; the best content of the water-reducing agent is 0.2% of the cement mass. A reasonable amount of fly ash and water-reducing agent can optimize the number of harmless holes and less harmful holes in the concrete to improve the frost resistance and strength after the freeze–thaw, and the frost resistance is F150. This study provides a theoretical basis and technical guarantee for the resource utilization of recycled aggregate in permeable pavement concrete. Full article

(This article belongs to the Special Issue Mechanical and Modeling of Composite Materials)

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