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16 pages, 13544 KiB

Open AccessArticle

Polypropylene Fiber’s Effect on the Features of Combined Cement-Based Tailing Backfill: Micro- and Macroscopic Aspects

by Xihao Li, Shuai Cao and Erol Yilmaz

Minerals 2024, 14(3), 212; https://doi.org/10.3390/min14030212 - 20 Feb 2024

Cited by 1 | Viewed by 573

In undercut-and-fill mining, backfills show weak tensile strength and poor ductility properties since they act as artificial pillars to support stope roofs. Hence, the enhancement of the stability of mining structures and backfills is a crucial requisite for underground mining backfill operations. This [...] Read more.

In undercut-and-fill mining, backfills show weak tensile strength and poor ductility properties since they act as artificial pillars to support stope roofs. Hence, the enhancement of the stability of mining structures and backfills is a crucial requisite for underground mining backfill operations. This study addresses the reinforcing effect of polypropylene (PP) on the strength features of combined cement-based tailing backfill (CCTB) with varied cement/tail ratios (c/t: 1:8 to 1:4) at both macroscopic and microscopic levels. Fill specimens containing a fixed solid content of 70 wt% were reinforced with fiber (0.6 wt%) and with no fiber (classified as a reference sample). They were then cast in mold sizes of 160 × 40 × 40 mm³, and cured for 7 days. Following curing, some experiments covering three-point bending assisted by DIC and SEM were performed to inspect the microstructure and strength features of CCTB. The results illustrate that the flexural strength of fiber-oriented CCTB increases along with the c/t fraction, but it is not greater than that of specimens with a high c/t fraction without fiber. Adding PP fiber, the peak deflection of CCTB specimens was improved, and the increment of peak deflection increased linearly with rising c/t fraction, enhancing CCTB’s bending characteristics. CCTB damage starts from the bottom to the middle, and the main cause of the damage is the stress distribution at the lowest section. The addition of fiber to CCTBs increases the ability to dissipate energy, which helps to hinder crack extension and prevent brittle damage from occurring. The microstructure shows that AFt and CSH were key hydrate materials in CCTB. As a result, this study develops the security of mining with backfill and helps to determine its design properties for safe production inputs and sustainable filling operations. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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20 pages, 8994 KiB

Open AccessArticle

The Influence of Multi-Size Basalt Fiber on Cemented Paste Backfill Mechanical Properties and Meso-Structure Characteristics

by Xi Chen, Huazhe Jiao, Juanhong Liu, Yixuan Yang, Xinming Chen, Liuhua Yang, Wenxiang Zhang and Tongyi Yang

Minerals 2023, 13(9), 1215; https://doi.org/10.3390/min13091215 - 15 Sep 2023

Cited by 2 | Viewed by 704

Abstract

As the mine enters the deep mining stage, there is a need to enhance the compressive strength and toughness of the backfill. The objective of this study is to examine the mechanical properties of cemented tailings backfill after the incorporation of multi-size fibers [...] Read more.

As the mine enters the deep mining stage, there is a need to enhance the compressive strength and toughness of the backfill. The objective of this study is to examine the mechanical properties of cemented tailings backfill after the incorporation of multi-size fibers and to validate the toughening mechanism of basalt fibers (BFs). To achieve this, a series of basic mechanical property tests for multi-size BFs mixing were devised, accompanied by industrial computerized tomography (CT) scanning and discrete element simulation. This study shows that the compressive strength increases and then decreases with the increase of BF dosage at a certain percentage of each size, and the splitting tensile strength gradually increases with the increase of BF dosage. The compressive strength tends to decrease and then increase, and the splitting tensile strength increases and then decreases as the fiber size ratio changes. The distribution of cemented tailings backfill and BF within the discrete element model is random. A few BF cannot play a bridging role; however, a moderate amount of BF is relatively uniformly distributed in the model to form a network structure, which generates a bond between the particles and the matrix and can effectively limit the expansion path of cracks and enhance the toughness. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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21 pages, 8185 KiB

Open AccessArticle

Polypropylene Fiber Effect on Flexural Strength, Toughness, Deflection, Failure Mode and Microanalysis of Cementitious Backfills under Three-Point Bending Conditions

by Ziyue Zhao, Shuai Cao and Erol Yilmaz

Minerals 2023, 13(9), 1135; https://doi.org/10.3390/min13091135 - 28 Aug 2023

Cited by 4 | Viewed by 915

Abstract

Cemented tailings backfill (CTB) is continually practiced in a large number of metallic mines for re-filling underground ore extraction areas. Re-filling these areas can boost the security of mining teams during construction. Hence, CTB’s durability/ductility is extremely vital to ensure the safety of [...] Read more.

Cemented tailings backfill (CTB) is continually practiced in a large number of metallic mines for re-filling underground ore extraction areas. Re-filling these areas can boost the security of mining teams during construction. Hence, CTB’s durability/ductility is extremely vital to ensure the safety of the entire mine. In this study, layered-fiber-reinforced CTB (LFR-CTB) was manufactured using polypropylene fiber (PPF) to increase the strength and flexibility of backfilling. The strength and bending features of CTB and LFR-CTB specimens were explored through a three-point bending test and SEM microanalysis. Test findings pointed out that the flexural strength of 14-day-cured CTB specimens without fiber delamination and with cement showed that a tailings ratio of 1:4 was the largest among others. Residual flexural strength of LFR-CTB was greater than those of CTB without fiber delamination. Accumulating fiber delamination effectively improved CTB’s flexural features. CTBs without fiber delamination presented the largest average flexural modulus values. LFR-CTBs presented greater average toughness index values than ordinary CTB specimens. Adding fiber facilitated the progress of CTB’s post-peak rigidity. LFR-CTBs containing high-fiber delamination dimensional height have excellent bending properties. The damage mode of all backfill specimens is chiefly tensile damage. The overall bonding of LFR-CTB specimens in the presence of interlayer interfaces is outstanding, not affecting their bending performance. Ettringite and CSH gels were found to be key hydration materials. The addition of fiber to the filling has an inhibitory impact on the extension of the cracks occurring within specimens. Finally, this study’s key consequence is to deliver a technical guideline and reference in order to reveal LFR-CTB’s enhancement and delamination mechanism for industrial applications. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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20 pages, 7976 KiB

Open AccessArticle

Study on Mechanical and Flow Properties of Cemented Sulfur Tailings Backfill Considering the Influence of Fiber Type, Fiber Content and Addition Method

by Wei Liu, Shenghua Yin, Yongqiang Hou and Minzhe Zhang

Minerals 2023, 13(8), 1105; https://doi.org/10.3390/min13081105 - 20 Aug 2023

Viewed by 703

Abstract

Previous studies have confirmed that for cemented tailings backfill, mechanical properties are improved through the addition of fiber. However, for fiber-reinforced cemented sulfur tailings backfill (FRCSTB), physical and flow properties are still unknown. In this paper, the changes in fluidity, splitting tensile strength [...] Read more.

Previous studies have confirmed that for cemented tailings backfill, mechanical properties are improved through the addition of fiber. However, for fiber-reinforced cemented sulfur tailings backfill (FRCSTB), physical and flow properties are still unknown. In this paper, the changes in fluidity, splitting tensile strength (STS) and uniaxial compressive strength (UCS) of cemented sulfur tailings backfill (CSTB) are analyzed in detail. Secondly, regarding the addition of glass fiber and polypropylene fiber, the changes in the fluidity, STS and UCS of the CSTB, resulting from the fiber length, fiber content and method of fiber addition used, were analyzed. Moreover, the relationship between the UCS and fiber content is established. Finally, the mechanism behind the influence of fiber and sulfur content on the mechanical properties of CSTB is revealed. The results indicate that with the increase in sulfur content, the fluidity of the tailings slurry exhibits exponential growth. During the process of increasing sulfur content, the UCS and STS of CSTB initially increase and then decrease, reaching maximum values at 12% sulfur content. Similarly, at a fiber content of 0.6%, the UCS and 28d STS of CSTB reach their maximum values. In terms of enhancing the mechanical properties of CSTB, the effectiveness of glass fibers surpasses that of polypropylene fibers. In addition, regarding the improvement of the UCS of CSTB, the mixed addition of fibers is obviously worse than that of fiber alone. However, in terms of enhancing the STS of CSTB, the mixed addition of fibers outperforms the single addition of polypropylene fiber. From a microscopic perspective, polypropylene and glass fiber are able to form strong cohesion with the cement–tailings matrix and effectively prevent the formation and expansion of pores and cracks. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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15 pages, 2061 KiB

Open AccessArticle

Experimental Study on Dense Settlement of Full-Tail Mortar under Mechanical Vibration

by Wei Lai, Keping Zhou, Feng Gao, Zheng Pan and Xiu Gao

Minerals 2023, 13(8), 1077; https://doi.org/10.3390/min13081077 - 13 Aug 2023

Viewed by 815

Abstract

There are some problems in the application of slurry preparation technology, such as wide fluctuation range of underflow concentration, long settling time and low efficiency of solid–liquid separation. This is an important basis for researching the thick settling law of tailings slurry under [...] Read more.

There are some problems in the application of slurry preparation technology, such as wide fluctuation range of underflow concentration, long settling time and low efficiency of solid–liquid separation. This is an important basis for researching the thick settling law of tailings slurry under the action of mechanical vibration and its influencing factors to solve these problems. To this end, a small vibration thickening testing machine and vibrating rod were designed and developed. Physical simulation experiments were conducted to analyze the settling characteristics of tailings slurry under different vibration duration, start time, vibration frequency, and vibration inertia single factors. The results show that: (1) Mechanical vibration can effectively accelerate the settling speed of tailings particles, but the relationship between them is a non-positive correlation, and mechanical vibration time control with in 5 mins is the best. With the delay of starting the vibration time, the final mass concentration first increases and then decreases. (2) As the vibration frequency increases, the final mass concentration of tailings settlement first increases and then decreases. When the eccentric vibrator speed is 6000 r/min, the best slurry settlement effect is achieved. (3) When the vibration inertia of the eccentric oscillator is 0.158 g·cm² and the final mass concentration reaches 70.1%, the settling time only takes 210 min. (4) The lower the slurry concentration, the faster the settling speed. As the initial concentration increases, the final thickening time is also gradually prolonged. The research results provide some insights for the rapid thickening technology of rake-free paste thickeners. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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22 pages, 5918 KiB

Open AccessArticle

Strata Movement of Gangue Grouting Filling in Subsequent Space for Coal Mining and Analysis of Its Practical Effects

by Tailong An, Zhongya Wu, Jixiong Zhang, Yexian Liu, Gang Duan, Nan Zhou and Hao Yan

Minerals 2023, 13(5), 609; https://doi.org/10.3390/min13050609 - 27 Apr 2023

Cited by 3 | Viewed by 1024

Abstract

There is a huge amount of solid waste generated in coal resource exploitation and utilization, leading to effects on the environment and hindering sustainable development. Aiming at the difficulty of disposal of coal-based solid waste from high-yield, high-efficiency mines, this research proposed a [...] Read more.

There is a huge amount of solid waste generated in coal resource exploitation and utilization, leading to effects on the environment and hindering sustainable development. Aiming at the difficulty of disposal of coal-based solid waste from high-yield, high-efficiency mines, this research proposed a technique of gangue grouting filling in subsequent space (GGFSS) for coal mining and explored the movement of key strata backfilled using GGFSS technique and surface deformation characteristics using theoretical analysis and a field measurement method. The results indicate that the equivalent backfilled ratio (EBR) when using GGFSS is defined as the ratio of the grouting volume to available void volume, which is mainly affected by bed separation void volume, grouting volume, and the void volume of the caving zone. Using an EBR ground control mechanical model, the changes in the displacement and bending moment of key strata with the variation of the EBR were investigated. The critical EBR for the rupture of key strata was determined to be 74.44%. On this basis, the calculation methods of equivalent mining height (EMH) and the subsidence factor of GGFSS were proposed and then a surface deformation prediction model of GGFSS was established based on the principle of the probability integration method. The predictions implied that, at an EBR greater than 75%, the surface deformation could be significantly reduced. Engineering applications verified the effect of GGFSS on the control of ground movement. In-situ measurements of concentration, density, and particle size of the filling body were all close to the those designed values: the GGFSS technique shows longer grouting duration and a larger amount of grouting and its filling body can support impervious key strata above the working face in a mine, significantly decreasing surface subsidence. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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17 pages, 13739 KiB

Open AccessArticle

Rheological and Strength Properties of Steel-Slag Cemented Paste Backfill: Link to Gypsum Type and Dosage

by Fan Wu, Bolin Xiao and Faguang Yang

Minerals 2023, 13(3), 421; https://doi.org/10.3390/min13030421 - 16 Mar 2023

Cited by 1 | Viewed by 1159

Abstract

This paper aims to study the effects of gypsum type and dosage on the rheological and strength properties of steel-slag cemented paste backfill (SSB-CPB) using fluorogypsum (FG), phosphogypsum (PG), and desulfurization gypsum (DG). Experimental results indicate that the yield stress and the viscosity [...] Read more.

This paper aims to study the effects of gypsum type and dosage on the rheological and strength properties of steel-slag cemented paste backfill (SSB-CPB) using fluorogypsum (FG), phosphogypsum (PG), and desulfurization gypsum (DG). Experimental results indicate that the yield stress and the viscosity of fresh SSB-CPB are the smallest when using FG, followed by PG, and the highest when using DG. The strength of hardened SSB-CPB is the lowest when using PG, regardless of curing time, and is the highest when using DG after 3 and 7 days of curing or FG after 14 and 28 days of curing. With the increase of DG dosage, yield stress and viscosity of fresh CPB increase, while the strength of hardened CPB first increases and then decreases. For the rheological properties, the zeta potential changes the yield stress of fresh SSB-CPB, while the internal particle size and pH affect its viscosity. For the strength property, regardless of the effect of gypsum type or dosage, the changes in the results of microscopic experiments for hardened paste and SSB-CPB are critical indicators that the strength of SSB-CPB varies. When steel slag dosage is 35%, the best gypsum dosage is 24% and gypsum type is DG in the SSB for backfill. The findings of this study contribute to an enhanced understanding of the backfill binder material, which has beneficials of lower greenhouse gas emission, avoidance of natural raw materials excavation, saving environmental taxes, and reducing backfill costs. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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16 pages, 10382 KiB

Open AccessArticle

Effect of Curing Temperature under Deep Mining Conditions on the Mechanical Properties of Cemented Paste Backfill

by Yong Wang, Yansen Cao, Chen Cao and Hongjiang Wang

Minerals 2023, 13(3), 383; https://doi.org/10.3390/min13030383 - 09 Mar 2023

Cited by 3 | Viewed by 1156

Abstract

Nowadays, the cemented paste backfill mining method is widely used in mines. Since the temperature of the mine increases with increasing mining depth, the influence of temperature on the mechanical properties of cemented paste backfill (CPB) require attention. To address the problem of [...] Read more.

Nowadays, the cemented paste backfill mining method is widely used in mines. Since the temperature of the mine increases with increasing mining depth, the influence of temperature on the mechanical properties of cemented paste backfill (CPB) require attention. To address the problem of less research on paste performance in high temperature environments, uniaxial compressive strength tests of CPB at different temperatures were performed, and it was observed that temperature had a significant effect on the CPB strength. The CPB strength at a curing temperature above 40 °C deteriorated in the later curing time period, CPB at 65 °C was “crisp”, and the strength was lower than 40 °C in 3~28 days. Microscopic tests, such as thermogravimetric analysis (TGA/DTG), X-ray diffraction (XRD) and scanning electronic microscopy (SEM) analysis, of the samples found that the coarsening of the pore structure of CPB was the main reason for the decrease in the strength caused by the increase in temperature. The effect of curing temperature on the deformation characteristics of CPB was studied. Different curing temperatures had a greater impact on the stress-strain curve and elastic modulus, and there was a linear relationship between the elastic modulus and strength. Finally, based on MATLAB, a back propagation (BP) neural network model of strength under different curing temperature conditions was established. Compared with the actual value and the predicted value, the average absolute error was less than 0.2 MPa, and the average relative error was less than 6%. This prediction model had a high accuracy. The research results provide a good reference significance for the strength design of CPB. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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18 pages, 5362 KiB

Open AccessArticle

Admixture Effects on the Rheological/Mechanical Behavior and Micro-Structure Evolution of Alkali-Activated Slag Backfills

by Xubo Ji, Xiaozhong Gu, Zhuoran Wang, Shuai Xu, Haiqiang Jiang and Erol Yilmaz

Minerals 2023, 13(1), 30; https://doi.org/10.3390/min13010030 - 25 Dec 2022

Cited by 16 | Viewed by 1744

Abstract

Recently, alkali-activated slag (AAS) has attracted extensive attention in cemented paste backfill (CPB) due to its low cost/CO₂ emissions and high strength benefits. However, a comprehensive analysis of the mechanical/rheological behavior and microstructure evolution of AAS-CPB using mineral admixtures is still lacking. [...] Read more.

Recently, alkali-activated slag (AAS) has attracted extensive attention in cemented paste backfill (CPB) due to its low cost/CO₂ emissions and high strength benefits. However, a comprehensive analysis of the mechanical/rheological behavior and microstructure evolution of AAS-CPB using mineral admixtures is still lacking. In this study, metakaolin (MK), fly ash (FA), and silica fume (SF) were employed to replace ground granulated blast furnace slag (GGBS) at various levels to formulate an alkali-activated binder, and the corresponding mechanical, rheological, and microstructure properties of CPB were investigated. The results suggest that FA tends to reduce CPB’s rheological and strength evolution and this negative effect increases with the FA dosage. The replacement of MK or SF increases the rheological parameters and thus diminishes fluidity and has positive or negative effects on strength depending on the replacement level and curing age. This study’s findings will contribute to developing a new scheme for lucrative and environmentally responsive multi-solid waste-based AAS-CPB in the field. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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14 pages, 3326 KiB

Open AccessArticle

Research on the Homogenization Evaluation of Cemented Paste Backfill in the Preparation Process Based on Image Texture Features

by Liuhua Yang, Jincang Li, Huazhe Jiao, Aixiang Wu and Shenghua Yin

Minerals 2022, 12(12), 1622; https://doi.org/10.3390/min12121622 - 16 Dec 2022

Cited by 11 | Viewed by 1124

Abstract

In China, cemented paste backfill (CPB) is a common treatment method after the exploitation of basic energy. The homogeneity of slurry influences the performance of CPB. However, the online monitoring and characterization of homogeneity lack relevant technologies and unified standards. This article discusses [...] Read more.

In China, cemented paste backfill (CPB) is a common treatment method after the exploitation of basic energy. The homogeneity of slurry influences the performance of CPB. However, the online monitoring and characterization of homogeneity lack relevant technologies and unified standards. This article discusses an online image analysis technique applied to the online monitoring of cemented paste backfill mixing, which is based on the evolution of the texture of images taken at the surface of the mixing bed. First, the grayscale distribution of the image obtained by the high-speed camera in the CPB preparation process was analyzed by Matlab and its variance (s²) was solved, and the texture features of the image were analyzed by the variance of grayscale distribution. Then, a homogeneity discriminant model (

c_{s t}

) was established. The results show that the variance value of the grayscale distribution of the slurry image increases rapidly at first, then gradually decreases, and becomes stable in the final stage since it turns a constant value. When the s² value tends to be stable, the slurry gradually reaches homogenization, and the discriminant coefficient of paste homogenization based on the homogenization discriminant model reaches 0.05. The homogenization prediction of CPB proves to be consistent with the backfill performance comparison results. The evolution of the texture allows obtaining important information on the evolution of different formulations during mixing, which can be used for intelligent monitoring of CPB preparation process. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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16 pages, 6141 KiB

Open AccessArticle

Mechanical Properties and Microstructure of Iron Tailings Cemented Paste Backfills Using Carbide Slag-Activated Ground Granulated Blast-Furnace Slag as Alternative Binder

by Yabin Feng, Feng Li, Wenyue Qi, Qiangsheng Ren, Wenyan Qi, Ge Duan, Kailin Zheng, Yongji Han and Haotian Pang

Minerals 2022, 12(12), 1549; https://doi.org/10.3390/min12121549 - 30 Nov 2022

Cited by 6 | Viewed by 1164

Abstract

For rational disposal of solid wastes, low-cost cemented paste backfills (CPB) were prepared with iron tailings, ground granulated blast-furnace slag (GGBS), and calcium carbide slag (CS). To ensure that CPB can be effectively utilized in mine backfill projects, the effects of solid contents, [...] Read more.

For rational disposal of solid wastes, low-cost cemented paste backfills (CPB) were prepared with iron tailings, ground granulated blast-furnace slag (GGBS), and calcium carbide slag (CS). To ensure that CPB can be effectively utilized in mine backfill projects, the effects of solid contents, GGBS content, CS/GGBS ratio, and mixing water on the workability and mechanical properties of CPB were investigated. The results indicated that when the solid content was 70%, the GGBS content was 14%, the CS/GGBS ratio was 0.4, the mixing water was tap water, the fluidity of fresh CPB slurry was 167 mm, and 28d unconfined compressive strength (UCS) of CPB reached 2.89 MPa, at which time the effect of the activation of the GGBS with CS was optimal. The analysis of X-ray diffraction (XRD), scanning electron microscopic imaging (SEM), thermogravimetric analysis (TG-DTG), and Fourier transform infrared spectroscopy (FTIR) demonstrated that the hydration products are mainly C-S-H gels, C-A-S-H, hemicarbonate, and hydrotalcite in CS-GGBS cementitious material. The C-S-H gel content gradually increased with increasing curing time and CS content (15%–35%). When the CS content was increased to 25%, the C-S-H gel content significantly increased, which improved the overall structural compactness and increased the UCS of CPB. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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15 pages, 4479 KiB

Open AccessArticle

The Rheological Properties and Strength Characteristics of Cemented Paste Backfill with Air-Entraining Agent

by Baogui Yang, Xiaolong Wang, Peng Yin, Chengjin Gu, Xindong Yin, Faguang Yang and Tao Li

Minerals 2022, 12(11), 1457; https://doi.org/10.3390/min12111457 - 18 Nov 2022

Cited by 4 | Viewed by 1004

Abstract

Clogging pipelines is one of the most common and urgent problems in paste backfill mining. The aim of the present study was to solve the problem of pipe blockage in paste backfill mining. In this paper, paste mixed with coal gangue, fly ash, [...] Read more.

Clogging pipelines is one of the most common and urgent problems in paste backfill mining. The aim of the present study was to solve the problem of pipe blockage in paste backfill mining. In this paper, paste mixed with coal gangue, fly ash, cement, and additives is used to investigate the influence of three air-entraining agents (AEAs) (including sodium dodecyl sulfate (SDS), triterpene saponin (SJ), and sodium abietate (SA)) on the flow characteristics and strength characteristics of the paste. A series of relevant tests was conducted on the paste, such as air content experiments, slump and expansion experiments, viscosity and yield stress tests, and the uniaxial compressive strength (UCS) test. The results show that the air content of the paste increases with increasing AEA content, but the increase is limited and reaches a maximum at 0.9 AEA. The slump of the paste increased by up to 10–13 mm, and expansion increased by up to 66–130 mm compared to the paste without AEA. The viscosity of the paste decreased by up to 0.13–0.20 Pa·s, and the yield stress decreased by 81.47%–93.7% of the original. The strength of the paste was also reduced, and after 28 days of curing, the strength was reduced by up to 1–1.2 MPa. Taking into account the strength requirement of 3 MPa for the paste from the Linxi mine, it was considered that the dosage of 0.9 B was a good choice, as it could better change the flowability of the paste and reduce the pipeline transportation resistance and transportation energy consumption. At the same time, the strength was also acceptable. The study in this paper can provide a reference for performance studies of pastes mixed with coal gangue, fly ash, cement, and additives as materials. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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13 pages, 2422 KiB

Open AccessArticle

Mechanism of Different Mechanically Activated Procedures on the Pozzolanic Reactivity of Binary Supplementary Cementitious Materials

by Xiaochuan Xu, Fengdan Wang, Xiaowei Gu and Yunqi Zhao

Minerals 2022, 12(11), 1365; https://doi.org/10.3390/min12111365 - 27 Oct 2022

Cited by 2 | Viewed by 1139

Abstract

In this study, a type of fly ash and iron tailing powder were used as a binary supplementary cementitious material (SCM) and two different mechanically activated procedures, named coalescent activation and separated activation, were carried out to improve the pozzolanic reactivity. Then, three [...] Read more.

In this study, a type of fly ash and iron tailing powder were used as a binary supplementary cementitious material (SCM) and two different mechanically activated procedures, named coalescent activation and separated activation, were carried out to improve the pozzolanic reactivity. Then, three binary supplementary cementitious materials were used to replace 30 wt% of ordinary Portland cement to develop cemented mortars, and the compressive strength, hydration products, and micro-structure were studied. The experimental results indicated that the activated supplementary cementitious materials increased the compressive strengths of the mortars by 5.4% and 13.2%, negligibly changed the hydration product types, and impacted the quantity only. The application of SCMs also prolonged the setting time and decreased the hydration rate, profiting the application. Simultaneously, the micro-pore structure was ameliorated, and the porosity decreased. Therefore, comprehensively considering the improved mechanical behavior and inexpensive cost, the activated binary SCM can be considered an ecological and economical admixture, especially for the coalescent activation procedure. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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13 pages, 6239 KiB

Open AccessTechnical Note

Direct Tensile Measurement for Cemented Paste Backfill

by Andrew Pan and Murray Grabinsky

Minerals 2023, 13(9), 1218; https://doi.org/10.3390/min13091218 - 16 Sep 2023

Viewed by 744

Abstract

Tensile strength is a crucial parameter involved in the design and analysis of cemented paste backfill (CPB). The ability of CPB to withstand tensile forces is essential for the stability of the backfilled stopes, particularly in areas with high stress or deformation. The [...] Read more.

Tensile strength is a crucial parameter involved in the design and analysis of cemented paste backfill (CPB). The ability of CPB to withstand tensile forces is essential for the stability of the backfilled stopes, particularly in areas with high stress or deformation. The tensile strength is a critical design parameter used in sill mats to perform underhand cut-and-fill operations. This study presents a novel technique that utilizes rectangular dog-bone specimens and compression to tensile load converters to perform the direct determination of tensile strength. This study indicates that the prevailing assumption regarding the ratio of unconfined compressive strength (UCS) to tensile strength (i.e., 10:1 or 12:1) underestimates the strength. The results suggest a ratio closer to 3:1 or 4:1. The findings indicate that the ratio varies with the curing interval. Specifically, the tensile-to-compressive strength ratios were higher in early-age specimens, as tensile strength values do not increase at the same rate as those of compressive strength. This disparity has notable implications, as underestimating tensile strength via traditional UCS-to-tensile strength ratios could potentially inflate binder consumption. Our study underscores the importance of using direct tensile strength measurements to optimize mining operations. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling)

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