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The macroscopic flow behavior and rheological properties of cemented paste backfill (CPB) are highly impacted by the inherent structure of the paste matrix. In this study, the effects of shear-induced forces and proportioning parameters on the microstructure of fresh CPB were studied. The size evolution and distribution of floc/agglomerate/particles of paste were monitored by focused beam reflection measuring (FBRM) technique, and the influencing factors of aggregation and breakage kinetics of CPB were discussed. The results indicate that influenced by both internal and external factors, the paste kinetics evolution covers the dynamic phase and the stable phase. Increasing the mass content or the cement–tailings ratio can accelerate aggregation kinetics, which is advantageous for the rise of average floc size. Besides, the admixture and high shear can improve breaking kinetics, which is beneficial to reduce the average floc size. The chord length resembles a normal distribution somewhat, with a peak value of approximate 20 µm. The particle disaggregation constant (k2) is positively correlated with the agitation rate, and k2 is five orders of magnitude greater than the particle aggregation constant (k1). The kinetics model depicts the evolution law of particles over time quantitatively and provides a theoretical foundation for the micromechanics of complicated rheological behavior of paste. [ABSTRACT FROM AUTHOR]

Copyright of Afyon Kocatepe University Journal of Science & Engineering / Afyon Kocatepe Üniversitesi Fen Ve Mühendislik Bilimleri Dergisi is the property of Afyon Kocatepe University, Faculty of Science & Literature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents and discusses the outcomes of an experimental study aimed at investigating changes in pore water pressure (PWP) in cemented paste backfill (CPB) materials incorporating polycarboxylate ether-based superplasticizer (PES). The research mimics real-world backfill field curing conditions, encompassing factors such as thermal (T; field curing temperatures), hydraulic (H; drainage conditions), mechanical (M; field vertical stress), and chemical (C; presence or absence of PES) factors. Utilizing a developed THMC backfill curing system, controlled THMC experiments were conducted to assess the impact of these factors and their interactions on pore water pressure (PWP) in CPB with or without PES. Results reveal that both individual THMC factors and their interactions significantly affect PWP development within CPB. The study also highlights the impact of PES on PWP in CPB, showing that adding 0.125% of PES can lead to a reduction in pore water pressure values by approximately 50% after 28 days of curing. Moreover, the results obtained demonstrated the effectiveness of the experimental THMC test techniques developed in this study in successfully mimicking field-like loading conditions, substantiating their usefulness for subjecting laboratory CPB samples to realistic loading scenarios in the field. These findings are of great importance for the mining industry and backfill designers, providing technical insights into complex THMC interactions affecting PWP in CPB-PES. Understanding these relationships is vital for optimizing CPB and barricade design, ensuring structural integrity, enhancing mine productivity, and guiding future research on numerical models for PWP prediction across all CPB structures. [ABSTRACT FROM AUTHOR]

Phosphogypsum (PG), a hard-to-dissipate by-product of the phosphorus fertilizer production industry, places strain on the biogeochemical cycles and ecosystem functions of storage sites. This pervasive problem is already widespread worldwide and requires careful stewardship. In this study, we review the presence of potentially toxic elements (PTEs) in PG and describe their associations with soil properties, anthropogenic activities, and surrounding organisms. Then, we review different ex-/in-situ solutions for promoting the sustainable management of PG, with an emphasis on in-situ cemented paste backfill, which offers a cost-effective and highly scalable opportunity to advance the value-added recovery of PG. However, concerns related to the PTEs' retention capacity and long-term effectiveness limit the implementation of this strategy. Furthermore, given that the large-scale demand for ordinary Portland cement from this conventional option has resulted in significant CO2 emissions, the technology has recently undergone additional scrutiny to meet the climate mitigation ambition of the Paris Agreement and China's Carbon Neutrality Economy. Therefore, we discuss the ways by which we can integrate innovative strategies, including supplementary cementitious materials, alternative binder solutions, CO2 mineralization, CO2 curing, and optimization of the supply chain for the profitability and sustainability of PG remediation. However, to maximize the co-benefits in environmental, social, and economic, future research must bridge the gap between the feasibility of expanding these advanced pathways and the multidisciplinary needs. [ABSTRACT FROM AUTHOR]

The substantial arsenic (As) content present in arsenic-containing bio-leaching residue (ABR) presents noteworthy environmental challenges attributable to its inherent instability and susceptibility to leaching. Given its elevated calcium sulfate content, ABR exhibits considerable promise for industrial applications. This study delved into the feasibility of utilizing ABR as a source of sulfates for producing super sulfated cement (SSC), offering an innovative binder for cemented paste backfill (CPB). Thermal treatment at varying temperatures of 150, 350, 600, and 800°C was employed to modify ABR's performance. The investigation encompassed the examination of phase transformations and alterations in the chemical composition of As within ABR. Subsequently, the hydration characteristics of SSC utilizing ABR, with or without thermal treatment, were studied, encompassing reaction kinetics, setting time, strength development, and microstructure. The findings revealed that thermal treatment changed the calcium sulfate structure in ABR, consequently impacting the resultant sample performance. Notably, calcination at 600°C demonstrated optimal modification effects on both early and long-term strength attributes. This enhanced performance can be attributed to the augmented formation of reaction products and a densified microstructure. Furthermore, the thermal treatment elicited modifications in the chemical As fractions within ABR, with limited impact on the As immobilization capacity of the prepared binders. [ABSTRACT FROM AUTHOR]

This paper examines the influence of various factors, including the addition of nano-calcium carbonate particles (chemical processes, C) to CPBs, non-isothermal field curing temperatures (thermal factor, T), and field vertical curing stress (mechanical factor, M), on the self-desiccation capacity of CPB plugs. The assessment of self-desiccation involves the determination of pore water pressure (PWP) and volumetric water content (VWC) in the examined CPBs. Thermo-mechanical-chemical (TMC) column experiments were conducted to investigate the interaction among these factors and their collective impact on the evolution of PWP and VWC within the CPB plug. The findings underscore that each factor, both individually and in combination, significantly affects the magnitude and progression of self-desiccation in CPB plugs. Notably, the factors of elevated field temperature and the introduction of nano-calcium carbonate (NC) to the CPB exert the most substantial influence on the extent and enhancement of self-desiccation, whereas the impact of field curing stress in isolation is comparatively much weaker. The integration of nano-calcium carbonate, especially under non-isothermal conditions and concurrent field stress, emerges as a key contributor to enhanced PWP and VWC dissipation rates. The role of non-isothermal field curing temperature is underscored as a significant contributing factor in the self-desiccation of CPB plugs. The results presented in this paper will contribute to a more cost-effective design of CPB plugs and the improved optimization of CPB mixtures with nano-calcium carbonate particles.

The purpose of this study was to investigate the effect of the use of rubber powder from tire recovery on the dynamic loading performance of CPB. Finally, it is concluded that using recycled rubber material to backfill mine paste is helpful in reducing waste tire pollution and improving the impact resistance of the backfill body. The dynamic compressive strength, Dynamic Increase Factor (DIF), peak dynamic load strain, and dynamic load elastic modulus of the samples composed of slag, Portland cement, wastewater, and rubber powder were determined. Through the analysis of the experimental data, it can be seen that the recycled rubber reduces the dynamic compressive strength and DIF of the specimen but increases the peak dynamic load strain and dynamic load elastic modulus and other characteristics, and enhances the ability of the filled body to absorb elastic strain energy. The results show that recycled rubber can increase the deformation ability of the filler and improve the impact resistance of the filler. The results of this study provide valuable information and industrial applications for the effective management of solid waste based on sustainable development and the circular economy. [ABSTRACT FROM AUTHOR]

Numerous waste iron tailings worldwide require eco-friendly treatment methods, with biotechnology being a promising option. However, bacteria survival in cemented paste backfill has been a persistent challenge. This study presents a method that adjusts the cementing solution composition (e.g. urea and calcium ions) to enhance Bacillus licheniformis biomass in backfill. This approach, free from additives, aims to determine the optimal cementing solution concentration for bacterial growth in backfill. The results indicate that a solution with 1.0 mol/L urea and 1.2 mol/L calcium ions has the highest strength, surpassing the control group by 4.56%. Quantitative analysis reveals that this solution enhances the production of calcium carbonate while reducing the content of calcium hydroxide (CH), the hydration product. The interplay between biomineralization and hydration reactions is explained by the fact that CH in hydration reactions contributes calcium ions to the biomineralization process, establishing a complementary relationship between hydration and mineralization products. This discovery opens up a novel path to integrate MICP with waste iron tailings recycling for cemented paste backfill. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Paste backfill prepared with ultrafine tailings often faces difficulties in meeting engineering requirements. To address the challenge of using ultrafine tailings, this work utilized a slag cemented ultrafine tailings paste backfill (SCUPB) composed of slag, Portland cement, and desulfurized gypsum as the cementitious materials, with a binder–tailing ratio of 1:4 and a solid mass concentration of 60%. The fluidity and compressive strength of the SCUPB were tested at 3 days, 7 days, and 28 days, while the microstructure and hydration process of the SCUPB were studied by scanning electron microscopy and isothermal calorimetry. The results reveal that the fluidity of the SCUPB decreases with the increase in the slag content and increases with the decrease in the c/g ratio. SCUPB attains the highest early compressive strength with a slag content of 70% and a c/g ratio of 3:2 (with the cement content at 18% and the desulfurized gypsum content at 12%). In this slag–gypsum–cement system, the combined activation of the slag by the cement and desulfurized gypsum exhibits a higher early compressive strength. This work utilized ultrafine tailings to prepare paste backfill that meets the engineering requirements, achieving the effective utilization of ultrafine tailings in mine backfilling projects. [ABSTRACT FROM AUTHOR]

Macroscopic and microscopic properties of cemented paste backfill (CPB) were studied through uniaxial compressive testing, acoustic emission (AE) monitoring, and microscopic feature analysis. The research shows that the uniaxial compressive strength (UCS) and elastic modulus have an exponential function type positive correlation with the increase in curing time and a polynomial function type with the rise of curing temperature; the mechanical parameters reach the maximum when the curing temperature is 40 °C. Increasing the curing time and curing temperature can promote the transition from shear crack to tensile crack. Increasing the curing time and raising the curing temperature both promote the transition of shear crack to tensile crack in the CPB. Overall, the crack mode is a combination of tensile and shear crack. At room temperature, the shear cracks dominates in the initial stage, but the proportion of the shear cracks decreases as the pressure increases in uniaxial compression test. At a curing temperature of 60 °C, the crack mode transitions to a tensile-shear mixed crack, with tension becoming the dominant crack mode. Microscopic analysis suggests an excellent linear correlation between the pore fractal dimension, UCS, and elastic modulus. When the pore fractal dimension decreases, the mechanical parameters also decrease. The pore fractal dimension can effectively characterize the macroscopic mechanical properties. Finally, the curing temperature is divided into two stages, with 40 °C as the dividing line for analysis. In the first stage, the increase in curing temperature effectively improved the mechanical parameters; in the second stage, the excessively high hydration reaction rate weakened the mechanical parameters. [ABSTRACT FROM AUTHOR]

In order to improve the mechanical properties of backfill, steel slag and straw fiber were used as materials to prepare backfill. The law of sand-cement ratio, mass concentration, steel slag content and straw fiber on strength and rheological parameters of backfill was analyzed by orthogonal test method, and the influence mechanism of steel slag content and straw fiber on physical properties of backfill was revealed. The results show that mass concentration exerts the most substantial impact on rheological parameters, emerging as a significant determinant. Moreover, the yield stress diminishes with escalating tailings-cement ratio, while it escalates with higher mass concentration, steel slag content and straw fiber content. Augmenting the tailings-cement ratio and steel slag content serves to impede the amplification effect of mass concentration on yield stress. Notably, the tailings-cement ratio emerges as the most influential factor affecting the uniaxial compressive strength (UCS) of the backfill, albeit the UCS diminishes with rising tailings-cement ratio. Elevating the mass concentration and steel slag content can counteract the debilitation caused by an increase in the tailings-cement ratio on the UCS of the backfill. Furthermore, heightened mass concentration can bolster the reinforcing impact of steel slag content on early UCS. The increase of tailings-cement ratio increases the size and range of the void inside the backfill, subsequently leading to the degradation of its macroscopic compressive strength. The adhesion between straw fiber and mortar matrix constitutes a pivotal factor in improving the integration of backfill, whereas steel slag contributes to improving the mechanical properties by enhancing the distribution of void structures within the backfill. This research not only offer data support and scientific guidance for the design of backfill ratio parameters but also facilitate the broader application of straw fiber and steel slag in mine backfilling operations.

If the cemented paste backfill (CPB) does not contact the roof, it will cause mining safety problems such as roof collapse, and the passive roof contact technology cannot effectively solve the problem. Therefore, the active roof-contact technology based on expansion agent was developed. The orthogonal experiments were carried out to study the influence of mass concentration, tailings-to-cement ratio and expansion agent content on the expansion ratio and mechanical properties of CPB. Through the range analysis of the expansion ratio and unconfined compressive strength (UCS), the significance of influencing factors on the expansion ratio and UCS was obtained. The experimental results show that the tailings-to-cement ratio has the greatest influence on the UCS, and the expansion agent content influence the expansion ratio more. The multivariate nonlinear regression models can accurately predict the expansion ratio and UCS of CPB. It is found that the sensitivity of expansion agent content to the expansion ratio decreases with the increase of tailings-to-cement ratio. According to the requirement of the mine for the expansion ratio and UCS, the expansion ratio and UCS were optimized by multi-objective optimization, and the optimal proportioning schemes suitable for the CPB in mines were obtained. Finally, the expansion mechanism was revealed by scanning electron microscope (SEM), and the evolution of the expansion agent with hydration process was analyzed. This study is of great significance to realize the roof-connect of metal mines, and has important practical value for the safe mining.

The present study conducted an extensive investigation into the durability of Na2SO4-activated binary slag cementitious materials for use in cemented paste backfill (CPB) under sulfate attack conditions. The primary objectives were to assess the feasibility of employing a cost-effective and environmentally friendly binder in CPB applications. Samples were subjected to exposure to Na2SO4 and MgSO4 solutions for a duration of 30 weeks, and multiple aspects including dimension stability, micro and macro mechanical strength evolution, changes in phase assemblage, microstructure following sulfate attack, and heavy metals leaching were examined. The study revealed that Na2SO4-activated binary slag (OPC-slag/S) exhibited superior resistance to sulfate attack, demonstrating enhanced dimension stability. Notably, sample OPC-slag/S displayed an increase in compressive strength, even after prolonged exposure to sulfate solutions for 30 weeks. This increase amounted to approximately 10.76% and 4.81% following exposure to Na2SO4 and MgSO4 solutions, respectively. The heightened resistance of binder OPC-slag/S to sulfate attack can be attributed to its low portlandite content and the early consumption of aluminates, primarily due to the formation of ettringite. This phenomenon effectively prevents the formation of detrimental and expansive products within the cement matrix during sulfate attack. On the other hand, CPB samples with binder OPC-slag/S showed the best performance in heavy metals immobilizaton capacity due to the high resistance to sulfate attack. In conclusion, this study underscores the potential of utilizing OPC-slag/S as a cost-effective and environmentally friendly binder for CPB applications in sulfate-rich environments.

There is a global upsurge in the use of cemented paste backfill (CPB) for various mining functions. However, the cost of the Portland cement binder is prohibitive, thus warranting strategies to reduce cement usage without overly diminishing the CPB quality. Since carbon dioxide is used for patented sand moulding processes, this study is premised on that physicochemical ability of CO2 to enhance the curing of consolidated inorganic materials. It evaluated the impact of carbon dioxide on the uniaxial compressive strength UCS and preparation cost of CPB standard samples (ASTM C109). The preparation cost was delimited to the purchase cost of the Portland cement. The backfill material was silica sand tailings with 4.5 wt.% Portland cement binder and a water-cement ratio of 7.6. Distilled water of pH 5.4 was used for the control samples while variable amounts of carbon dioxide were dissolved in distilled water to generate carbonated mixing water with pH values of 3.8; 4 and 4.2. The lower the carbonated water pH, the higher is the CO2 concentration. UCS tests were conducted on the samples after curing for 3, 7, 28, and 90 days. There was an observable increase in the UCSs and reduction in curing time with increasing carbon dioxide. Samples prepared with carbonated water of pH 3.8 had almost double the strength of those prepared with pure distilled water of pH 5.4, implying that more dissolved CO2 corresponds to higher CPB strength. This is supported by the trendline equations for the graphical simulation of strength on curing time. Thus, CPB with much less binder can be expected to attain the requisite UCS if carbon dioxide is incorporated. The average reduction in Portland cement consumption was 0.61 %, which translates to a cost saving of the same percentage points. If calculated over the operational life of a mine, this is a massive saving of millions of dollars.

In the field of coal mine backfilling, the method of grading the coal gangue and the effect it has on the rheological properties of the cemented paste backfill (CPB) are still to be fully understood. In this study, the CPB is composed of coal gangue as the coarse aggregate, fly ash and cement as the fine aggregate. The properties of the coal gangue were characterised in terms of porosity and friction angle, and the comprehensive influence of different coal gangue grading, volume fraction and CPB mixture ratios on the rheological properties of the CPB was investigated. The experimental results indicate that both large and small coal gangue particle sizes can increase the porosity and friction angle. Compared with single grade and gap grade, coal gangue with continuous grade (G32) has a lower porosity of 42.1 %, a friction angle of 43.8 °, a yield stress of 7.6Nm and a viscosity of 6.5Nm, a higher slump of 221 mm, and a water film thickness of 1.68 μm. The yield stress has been identified as the primary factor influencing the slump of CPB. The yield stress and viscosity of the CPB are negatively correlated with the particle size, mortar ratio, and slump, and positively correlated with the volume fraction of coal gangue. In addition, the significant impact of various factors on the rheological parameters of the CPB is ranked as porosity> mortar ratio >volume fraction>friction angle. The relationship between yield stress, viscosity and water film thickness (WFT) is a power function, and the established WFT model can conveniently and quickly predict the rheological parameters of the CPB.

Solid waste filling is an important development direction for filling mining. This research proposes the preparation of solid waste-based cemented paste backfill (SWCPB) to fill the underground mined area by using waste rock and copper slag as the mixed aggregate and granulated blast furnace slag, steel slag, and desulfurization gypsum as raw materials of solid waste binder to reduce the environmental hazards caused by the industrial solid wastes. Based on the response surface method, experiments are designed to analyze the effect patterns of different factors on the mechanical properties of SWCPB. The formation mechanism of SWCPB mechanical properties is explored based on various microscopic analysis techniques. The mix proportions of SWCPB are designed based on machine learning. The results show that the strength of SWCPB increases and then decreases with the increase of the proportion of copper slag, and gradually increases with the increase of the steel slag dosage and binder-aggregate ratio. The alkaline environment provided by the steel slag causes the glass body in granulated blast furnace slag to depolymerize and react with desulfurization gypsum to produce hydration products, which are the main source of mechanical properties formation in SWCPB. The machine learning model constructed in this research paper has high prediction accuracy for the strength of backfill, which can achieve high-precision optimization of backfill mix proportion. The research results could guide the recycling of solid waste and the efficient use of filling mining technology.

To promote the sustainable exploitation of open-pit coal resources, waste is used as backfill material to realize the comprehensive utilization of solid waste mine resources. We proposed a mining method that is a combination of the highwall mining and filling mining methods. Cemented paste backfill (CPB) samples were prepared with high-clay-mineral-content marl particles as aggregate and normal Portland cement, sulfoaluminate cement and gypsum as cementing materials. The physical and mechanical properties and microstructural evolution of CPB with different binder ratios under wetting–drying cycles were measured. The results showed that the CPB with 0–3 wetting–drying cycles underwent shear and tensile coalescence, and that with 4–10 cycles underwent shear coalescence. The unconfined compressive strength (UCS) and elastic modulus (EM) decreased exponentially with increasing number of wetting–drying cycles but decreased exponentially and cubically with increasing porosity, respectively. The EM is more sensitive to gypsum content than the UCS. CPB deterioration was divided into an initial deterioration stage and a secondary deterioration stage. The evolution curve of the total damage variable presents an 'S' shape, with an initial damage stage, an accelerated damage expansion stage, a decelerated damage expansion stage and an end damage stage. The research results provide a basis for improving the recovery rate of resources under highwall conditions, and the extensive utilization of stripping materials, and promote the coordinated development of coal resource exploitation and environmental protection. [ABSTRACT FROM AUTHOR]

Given that many mines around the world are located in areas where fresh water is scarce, and companies are being held to increasingly stringent sustainability and environmental responsibility standards, many mines are looking to use locally available saline groundwater or seawater as mixing water in cemented paste backfill (CPB). However, the impacts of this decision on key engineering properties of CPB (e.g. strength and self-desiccation) that affect its mechanical stability need to be better understood to allow confident selection of this practical and more sustainable solution. Thus, the effect of mixing water salinity and binder type on the strength (unconfined compressive strength, UCS) development and self-desiccation (measured by suction and volumetric water content) of CPB is explored in this research. NaCl concentrations from 0 to 300 g/L were used in CPB made with silica tailings and Portland cement type I (PC). Concentrations of 10 and 35 g/L were found to moderately increase UCS, while a concentration of 100 g/L had comparable UCS to non-saline CPB and a concentration of 300 g/L was found to significantly decrease UCS over all curing times. The overall trend is 10 g/L > 35 g/L > 0 g/L > 100 g/L > 300 g/L. The UCS of the 60-day-old CPB with a NaCl of 300 g/L is significantly lower, registering a 26% decrease compared to the UCS of the 60-day-old CPB without salt. In contrast, the UCS of the 60-day-old CPBs containing 10 g/L and 35 g/L of salt exhibits a notable improvement, being 15% and 10% higher, respectively, than the UCS of the 60-day-old CPB without salt. Water content and suction monitoring were conducted up to 28 days of curing time, and it was found that suction only slightly contributed to UCS gain of the saline CPB, and high salt contents (100 and 300 g/L) significantly inhibited the self-desiccation ability of CPB due to inhibition of cement hydration by the excessive amount of salt. The increase in strength of both saline and non-saline samples was attributed primarily to the increase in cement hydration products, while the increased strength of the samples with salinities of 10 and 35 g/L was mainly attributed to the enhancement of the binder hydration due to the low amount of salt and the presence of Friedel's salt in the pores. The effect of PC replacement by 25 to 75% with slag on CPB with 35 g/L mixing water salinity was also studied. Slag replacement of 50% and higher resulted in significantly higher UCS over most curing times. Suction likely moderately contributed to UCS of the saline CPB with slag, in addition to the presence of Friedel's salt in the pores and the acceleration of cement and slag hydration by the presence of NaCl. [ABSTRACT FROM AUTHOR]

Flocculent is commonly used in mining activities to improve the concentration of tailing slurry by enhancing the sedimentation process of small tailings particles. The presence of flocculent in thickened tailings is unavoidable, and it affects the heavy metal leaching performances and mechanical and rheological characteristics of tailing-based cemented paste backfill (CPB). This study is carried out to investigate the physicochemical and leachability of CPB amended with flocculants and lime-activated ground granulated blast-furnace slag (GGBS). The stabilized samples were subjected to a series of model tests, including toxicity characteristics leaching procedure (TCLP) and pH, unconfined compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction. Moreover, the CPB amended with anionic polyacrylamide (APAM) demonstrated better performance in terms of a decrease in heavy metal leachability besides higher mechanical strength than poly aluminum chloride (PAC) and poly ferric chloride (PFC) samples. Furthermore, the UCS results showed that increasing binder content up to 15% negatively influences strength improvement of all stabilized samples because of weak connections between soil particles and cementitious material, resulting in high leachability of heavy metals. The analysis of XRD and SEM showed that anionic polyacrylamide (APAM) cases exhibited more voluminous hydration products, resulting in a compact stabilized matrix and substantially reduced heavy metal leachability. [ABSTRACT FROM AUTHOR]

The ordinary Portland cement (OPC) as usual binder is widely used for the backfilling in the Zijinshan Copper mine of Fujian province, whereas it leads to high cost of cemented paste backfill (CPB) every year. The main objectives of this study were to investigate the effect of low-calcium fly ash (LCFA) substituting for OPC on the compressive strength of CPB samples, through treating LCFA with mechanical and chemical action method to improve its pozzolanic activity. The experiment results show that the compressive strength of CPB samples is not increased when the non-treated LCFA is added into substitute for partial OPC. However, the compressive strength is obviously improved by the replacement of partial OPC with treated LCFA. When the substitution ratio of treated LCFA is 29.8%, the 28-day compressive strength of CPB samples with binder/tailing ratio of 1:6 achieves 3.9 MPa, and is 1.95 times higher than that of CPB samples with OPC as sole binder under the same condition. The economic analysis result exhibits a partial replacement (29.8%) of OPC with treated LCFA can save 28.7% of cemented backfill cost, indicating great economic benefit for underground backfilling mining. [ABSTRACT FROM AUTHOR]

Cement paste backfill (CPB) suffers serious damage and deterioration under the dual erosion conditions of the dry–wet cycle caused by the high chloride salt concentration in mine water and the fluctuation of mine water level. In order to discuss the mechanical properties and permeability characteristics of CPB under erosion, this study designs an immersion experiment for CPB under chloride salt and dry–wet cycle conditions. Through a uniaxial compressive strength (UCS) test, the change law for the mechanical parameters of the CPB was investigated, the strength constitutive equation of the CPB was constructed and the deterioration process of the CPB was analyzed. The penetration test was used to investigate the diffusion characteristics of the packing under chloride salt and dry–wet cycle conditions. The results showed that the strength and Young's modulus of the CPB initially increased and then rapidly decreased, with maximum decrease rates of 32.2% and 38.2%, respectively. The CPB structure exhibits an initial undamaged stage, an initial damaged stage, a damaged development stage, a damaged destruction stage and a residual damaged stage. The chloride ion penetration depth gradually increased with the number of dry–wet cycles, with a maximum diffusion depth of 20.5 mm. The maximum apparent diffusion coefficient of chloride ion was 18.99 × 10−10 m2/s, and the maximum concentration was 0.303 mol/L. Under the double erosion conditions of chloride salt and dry–wet cycle, the CPB structure was severely damaged. [ABSTRACT FROM AUTHOR]

In this paper, the effect of ternary binder containing Portland cement type I (PCI), slag, and limestone (LS) powder in varying proportions on the suction development and the mechanical strength of cemented paste backfill (CPB) was investigated. Mechanical tests, microstructural analyses (thermo-gravimetry analysis (TG/DTG) and mercury intrusion porosimetry), and monitoring (suction, electrical conductivity, and temperature) experiments were conducted on CPB. In the first part of this study, binary binders with two different PCI:slag proportions, 50:50 and 80:20, were examined with no LS, followed by the slag replacement with increasing weight percentages of LS from 0% to 20% by weight of the total binder, with constant cement content. The results indicate that the slow slag hydration kinetics decreased the suction and strength gain rate at a young age in the binary sample with high slag content (50 wt.%); however, its latent hydraulic and pozzolanic properties enhanced the strength gain at a later age, from 28 days. The addition of 5 wt.% and 10 wt.% LS to the ternary binder system improved the early age strength of CPB up to 7 days and 1 day, respectively, compared with the binary control samples, i.e., CPB with slag and without LS. While the addition of up to 10% LS to the ternary binder improved the rate of suction development and increased suction at early ages, beyond 10%, the addition of LS slightly decreased mechanical performance at all ages. Overall, the results obtained reveal that up to 50 wt.% slag with up to 10 wt.% LS with cement could be used as a ternary binder to improve the early age strength and suction development rate of CPB studied without significant loss in compressive strength at advanced ages. The results of this research could be of great benefit to the mining industry through the use of a ternary binder to replace cement, which could improve the overall performance of the CPB system, facilitate a more sustainable CPB design, and improve tailings management practices and overall economics. [ABSTRACT FROM AUTHOR]

Spontaneous combustion gangue (SCG) is often used as aggregate in traditional cemented paste backfill (CPB) for mine backfill, but the activation of SCG is insufficient. To stimulate the activity of SCG for the preparation of spontaneous combustion gangue-granulated blast furnace slag backfill (SGB), a new CPB was prepared by activating SCG via a mechanochemical composite activation method and adding ground granulated blast furnace slag (GGBS) to improve its activity. The mixing ratio was optimized by the response surface method and satisfaction function, and the strength formation mechanism was analyzed by scanning electron microscopy–energy dispersive spectrometer (SEM–EDS) and Fourier transform infrared spectroscopy (FTIR). The results showed that SCG had a certain pozzolanic activity, and the optimal grinding time was 30 min. The optimal mix ratio was 82.58% mass concentration, 2.93% alkali content, 30% GGBS content, and 52.92% fine gangue rate. Calcium silicate hydrate (C-S-H) gel and calcium aluminate sulfate hydrate (C-A-S-H) gel were the main reaction products of backfill, and with increasing curing age, C-S-H gel in the reaction system was gradually converted into C-A-S-H gel. FTIR analysis results showed that there were H-O-H, Si-O, and Si-O-T (T was Si or Al) bonds in the product, indicating that C-S-H gel and C-A-S-H gel were formed in the product. A new damage constitutive model was developed. The damage constitutive model could completely describe the backfill stress-strain curve. The study verified the feasibility of preparing cemented paste backfill with SCG and GGBS, which was beneficial to clean coal mine production and environmental protection. [ABSTRACT FROM AUTHOR]

The unconfined compressive strength (UCS) of alkali-activated slag (AAS)-based cemented paste backfill (CPB) is influenced by multiple design parameters. However, the experimental methods are limited to understanding the relationships between a single design parameter and the UCS, independently of each other. Although machine learning (ML) methods have proven efficient in understanding relationships between multiple parameters and the UCS of ordinary Portland cement (OPC)-based CPB, there is a lack of ML research on AAS-based CPB. In this study, two ensemble ML methods, comprising gradient boosting regression (GBR) and random forest (RF), were built on a dataset collected from literature alongside two other single ML methods, support vector regression (SVR) and artificial neural network (ANN). The results revealed that the ensemble learning methods outperformed the single learning methods in predicting the UCS of AAS-based CPB. Relative importance analysis based on the best-performing model (GBR) indicated that curing time and water-to-binder ratio were the most critical input parameters in the model. Finally, the GBR model with the highest accuracy was proposed for the UCS predictions of AAS-based CPB.

The scientific filling effect characterization is very important for backfill mining. A new filling effect index, the final backfill ratio (FBR), is proposed through experimental tests and theoretical analysis, and the sensitivity of FBR is studied in this paper. The control method of FBR is obtained and applied to optimise the filling effect for the backfill panel in Kailuan Group in China. It is concluded that every 0.05 m reduction of the void between the filling body and roof corresponds to 1.87% increase in FBR. FBR increases by 1.47% and 3.15% respectively when the UCS of the backfill body increases from 2MPa to 3MPa and 4MPa. [ABSTRACT FROM AUTHOR]

Cemented Paste Backfill (CPB) undergoes transient changes in stress behaviour during curing, influenced by geothermal gradient and cement hydration. This study explores CPB's response to temperature variations in a semi-confined narrow wall, simulating mining stope conditions. The results revealed that arching effects restricts vertical expansion of CPB slurry leading to temperature-induced thermal stress that often exceeding total stress estimation. Temperature change at different stage of backfill resulted in different level of stress generated due to the material state. These findings suggest the need to consider thermal behaviour in the relevant designs to improve safety in the mining industry. [ABSTRACT FROM AUTHOR]

Mine stopes are often characterised by near-saturate conditions from constant water inflow from the ore body. Although significant research has been conducted on mechanical properties of cemented paste backfill, there are limited studies on curing practices that reflect saturate conditions. This study examines the effects of submerged curing to simulate saturate conditions. The results indicate that observed dark grey colouration associated with submerged curing is similar to 'greening effect' observed in concrete material containing Ground Granulated Blast-furnace Slag. Our study indicates that submerged curing has limited adverse material effects and is effective in simulating near-saturated conditions. [ABSTRACT FROM AUTHOR]

Binder is the main cost burden in cemented paste backfill (CPB) and an obstacle towards fully green mining technologies. In this work, an improved, low-cost, efficient, and green binder with steel slag content up to 50 wt% was presented for mine backfill. The binder hydration and CPB hardening properties were experimentally investigated. Results show that the CPB with green SS binder (50 wt% steel slag, 35 wt% blast furnace slag, 15 wt% desulphurisation gypsum) has the highest 28-day strength of 2.21 MPa, which is 2 times higher than the Portland CPB control (0.98MPa). The green binder has less hydration heat and a slower and longer deceleration stage duration. The hydration products of the green binder are mainly ettringite and amorphous gel. The substantial gel-like products obtained from multiple activation processes are the mystery of the outstanding CPB strength. The hardening process of green binder CPB can be divided into fast hydrating stage, compacting stage, and potential refining stage. The findings can help better understand the steel slag CPB properties and improve solid waste valorisation and sustainable development of the mining, mineral processing, and iron and steel making industries. [ABSTRACT FROM AUTHOR]

With the increasing depths of underground mines due to the scarcity of near-surface ores, the introduction of fibre-reinforced cemented paste backfill (F-CPB) has emerged as a novel solution to address the demanding geomechanical conditions in deep mining operations. However, the widespread adoption of F-CPB in mining and industrial backfill operations necessitates a comprehensive understanding of its key engineering properties, including strength, yield stress, modulus of elasticity, and cost. Moreover, it is crucial to investigate the influence of the constituent materials (water, fibres, binders, tailings) and their interactions on these properties. This research paper presents the application of response surface methodology (RSM) to model the effects of binder content (Portland cement/Slag), water content, fibre content, tailings and their interactions on the mechanical and rheological properties, as well as the cost of F-CPB. Central Composite Design (CCD) experiments were conducted, and a high degree of agreement was observed between the experimental and predicted responses. The RSM approach proves suitable for accurately estimating the responses and assessing the interactions between the model parameters and the properties of F-CPB. Furthermore, a combination of RSM and the desirability approach enables the development of an optimisation tool for F-CPB, facilitating the formulation of optimal backfill mixtures. The results obtained from this study highlight the effectiveness of the combined RSM and desirability approach in F-CPB mix proportioning, offering an advanced engineering approach to F-CPB mix design. The proposed design method has the potential to reduce the laboratory testing protocol required for determining the optimal mix composition. [ABSTRACT FROM AUTHOR]

External sulphate attack (ESA) interferes with spatial changes in fracture toughness of cemented paste backfill (CPB) and affects its mechanical stability. Large-scale curing column models are developed to investigate the spatial evolution of mode-I and mode-II fracture toughness (i.e. KIC and KIIC) under seepage- and diffusion-induced ESA. It has been found that the seepage-induced ESA leads to spatial changes in KIC and KIIC of CPB at advanced ages and higher extent of degradation of fracture toughness is measured at a deeper position in CPB. Comparatively, KIc can be used as a reliable quantity to estimate KIIc under the diffusion-induced ESA. [ABSTRACT FROM AUTHOR]

The influence of underground humidity on the mechanical performance of cemented paste backfill (CPB) in metal mines is a problem that cannot be ignored. To this end, this paper conducted the curing experiments of CPB samples under different curing humidity (60%, 80% and 95%). Physical properties such as moisture content and dry density as well as mechanical properties such as uniaxial compressive strength, cohesion and internal friction angle of the CPB samples were monitored during fixed curing time (3, 7, 14 and 28 days). TGA/DTG, XRD and SEM were used to analyse the microstructure of CPB samples under different curing humidity at 3 and 28 days, and a BP neural network prediction model of CPB strength was established based on the obtained data. The results show that the curing humidity has a great influence on the physical and mechanical properties of the paste, and the amount of hydration products and the change of pore structure are the main reasons that affect the properties. In order to ensure the safety and economy of the CPB structure, the influence of environmental humidity on the paste should be considered in the filling design. [ABSTRACT FROM AUTHOR]

This study investigates the time-dependent rheological behavior of cemented paste backfill (CPB) that contains calcined clay as a binder, particularly with LC3 (Limestone Calcined Clay Cement) compositions, using two different PCEs (Polycarboxylate Ether) superplasticizers. Rheological measurements have been conducted on four different mix designs using the Bingham model to describe the CPB mixtures. Both yield stress and plastic viscosity have been reported, and the impact of the admixture on these parameters has been investigated. Unconfined compressive strength (UCS) was measured over 182 days for all mix designs. Both admixtures showed better workability in all cases, with significantly improved yield stress and plastic viscosity compared to the reference, while showing little to no negative impact on strength over time. This study highlights that both from a binder and an admixture point of view, relevant to the industry, these calcined clay systems are ready to be used in a CPB and could make a significant impact on the sustainability of a mining operation in the near future. [ABSTRACT FROM AUTHOR]

Cement paste backfill (CPB) is an effective waste management method allowing the storage of fine process tailings into underground mined-out voids. CPB performance generally depends on the properties of the tailings and the type of binder. In recent years, there has been an increasing trend in the use of alkali-activated slag (AAS) to improve the performance properties of CPB. This study focuses on the ultrasonic and microstructural investigation of the effect of slag fineness on the mechanical, geochemical, and durability properties of sulphide-rich tailings CPB made of AAS (AAS-CPB) over 360 days. In this scope, the AAS-CPB samples were prepared at three different slag fineness values (3100–4650–6300 cm2/g). According to the findings, the fineness of the slag significantly improved the early-age and long-term strength (~2.3-fold and ~6.6-fold, respectively) of the CPB samples (CPBs). However, a further increase in the slag fineness was observed to impair the CPB microstructure and strength in the long term. Ultrasonic pulse velocity monitoring displayed a very high relation with the strength evolution of the CPBs and is a very reliable method for the durability assessment of the CPBs. Slag fineness around 4600 cm2/g was found to be sufficient for CPB preparation, and was seen to improve the pore structure evolution of the AAS-CPB. Microstructural studies are in good agreement with the geochemical and durability behaviour of the AAS-CPB at this fineness. Microstructural and ultrasonic findings suggest that, while slag fineness enhances the mechanical and microstructural properties of the AAS-CPB, a further increase in the fineness of the slag has no additional technical advantages. [ABSTRACT FROM AUTHOR]

In underground mining, the application of mine backfill has evolved into a standard practice. Mine backfill typically consists of tailings, water, and hydraulic binders. However, the high cost of binders has prompted scholars to research alternatives to reduce this cost while maintaining or even improving the properties of the backfill. One potential alternative is leveraging microwave irradiation. In this study, an innovative approach was developed to increase the unconfined compressive strength (UCS) of early age cemented paste backfill (CPB). Microwave treatment was applied to CPB samples at various curing ages for varying durations. The UCS and ultrasonic pulse velocities were measured and analyzed in an experiment with a full factorial design. Moreover, the microstructural properties of the CPB were investigated using mercury intrusion porosimetry. The results indicate a significant potential to increase the UCS of CPB by up to 25% when microwave-treating samples for 8 min after 7 days of curing. This approach could shorten mining cycle times and improve productivity, presenting a promising method to enhance CPB strength. [ABSTRACT FROM AUTHOR]

This research aims to examine the impact of sodium silicate (SS) on the mechanical and microstructural properties of cemented paste tailings or cemented paste backfill (CPB), a cementitious construction material extensively used in underground mining operations. The study involved various compositions and curing conditions of SS-CPB samples, and their uniaxial compressive strength (UCS), stress–strain behavior, microstructure, and modulus of elasticity were evaluated by conducting mechanical (UCS) and microstructural (DT/DTG, MIP) tests, as well as monitoring experiments. Findings indicate that SS improves the mechanical strength of CPB and enhances its microstructure. The development of UCS is affected by SS dosage, curing time, water chemistry, curing temperature, and curing stress. Higher SS dosage, curing time, temperature, and stress lead to higher UCS, while sulfates decrease UCS. SS also increases CPB's resistance to sulfate attack, and field curing temperature improves the binder hydration enhancement induced by SS. The presence of SS affects the stress–strain properties of CPB, including the shape of the stress–strain curve, maximum stress and strain, and modulus of elasticity. The modulus of elasticity of CPB with SS is higher than that without SS under field thermal curing conditions. Moreover, UCS and the modulus of elasticity have a linear relationship in SS-CPB, regardless of SS content. A relationship is proposed to estimate the modulus of elasticity of SS-CPB from its UCS. The study has significant practical implications for the cost-effective design of mine CPB structures and for improving underground mine work safety and productivity. [ABSTRACT FROM AUTHOR]

This study aims to research the implications of rubber powder utilisation, from tires recycling, in the deformability and strength properties of CPB. In the end, it will be concluded that mine paste backfill with recycled rubber materials contributes to the decrease of waste tire pollution and improve some mechanical properties of the filling body. For that purpose, tests were carried out to determine the uniaxial compressive strength, the elastic energy of deformation, Young's modulus, and Poisson's ratio in specimens made up of mine tailings, Portland cement, wastewater, rubber powder, and plasticisers. The analysis of experimental data determines that recycled rubber makes fresh slurry have better performance in flow characteristics. In the hardened state, recycled rubber reduces the uniaxial compressive strength of the specimens and Poisson's ratio, but other features like deformability increase (Young's modulus decrease) that enhance the ability to absorb elastic strain energy of the filling body. As a result, the study indicates that recycled rubber is applicable to rockburst prevention. The findings of this study provide both invaluable information and industrial applications for the efficient management of solid waste, based on sustainable development and circular economy. [ABSTRACT FROM AUTHOR]

This paper presents the effects of a full-range water-reducing (FRWR) admixture on the key engineering properties of cemented paste backfill (CPB). CPB samples with a certain slump are prepared with 4.5% cement by mass of the tailings and different dosages of an FRWR admixture (superplasticizer contents of 1%, 3%, and 5%) to evaluate their water demand during hydration, rheological properties, self-desiccation ability, and microstructural and mechanical properties. Moreover, cement paste samples with a high water-to-cement ratio (w/c = 2) which are used to model the cement matrix of the CPB are prepared for x-ray diffraction (XRD) scanning and thermal analyses (TAns). The results show that the addition of an FRWR admixture to the studied CPB can reduce its water demand by up to 23% and significantly increase its strength from 1.0 MPa to 2.38 MPa (by approximately 2.4 times) at 28 days. The pore volume of the CPB samples is also significantly reduced from 27.17 to 18.27% due to the capability of the FRWR admixture to reduce water demand. Also, the addition of an FRWR admixture to the CPB results in a substantial decrease (up to 83%) of its yield stress, thereby improving its flowability. The CPB samples with an FRWR admixture are found to have a higher negative pore water pressure, i.e., higher self-desiccation, than the CPB sample without an FRWR admixture. The microstructural analysis also shows that the FRWR admixture has an increasing effect on the hydration products in the CPB mixture. [ABSTRACT FROM AUTHOR]

Estimating the as-placed properties of mine backfill is fundamental to optimizing the safety and productivity of underground mines. For cemented paste backfill (CPB), an important consideration is the extent to which self-weight consolidation during deposition may reduce the void ratio and enhance the binder's effectiveness. Field monitoring and sampling campaigns can help investigate this phenomenon but they are expensive and logistically difficult. Therefore, mesoscale column experiments are performed in the controlled laboratory environment to better understand the coupling between self-weight consolidation and cement hydration. In this paper, columns are backfilled with uncemented paste tailings and with CPB and the pore water pressure, electrical conductivity, and volume changes are monitored during and after backfilling. The pore water pressure profiles at the end of backfilling are compared with an available analytical solution and restrictions on the solution's validity are identified. Void ratios of samples taken from columns are compared with the ones obtained from field samples and the similarity indicates the filling conditions simulated in the laboratory are representative of field conditions. The changes in void ratio after curing were small compared to the initial void ratio of fresh CPB. The tests' results help explain why self-weight consolidation during backfilling is not significant at the studied mine, which may be the case for many other mining operations as well. [ABSTRACT FROM AUTHOR]

The rapid concentration of tailings is a crucial initial step in the cemented paste backfill (CPB) process, as it ensures the stability of the backfilling slurry concentration and the continuity of the backfilling process. The structure of flocs plays a pivotal role in tailings concentration, directly contributing to such critical technical parameters as settling speed and bottom flow concentration. However, most of the current studies focus on flocculant addition rather than the tailings slurry itself. Also, there is a lack of uniform characterization of the flocculant structure in the flocculation and settling system. This study establishes a semi-quantitative assessment system for evaluating the fine structure of tailings flocs based on indicators such as the exposure state of coarse particles, floc size, and floc compactness (porosity). The findings reveal that, during the settling process, the higher true density of tailings (3.156 g/cm3) and intermediate particles (40 wt% of 38 μm–74 μm particles) attenuates the clamping effect of turbulence on settling, leading to a faster settling rate to 0.65 cm/s and 0.29 cm/s respectively. Moreover, in the thickening process, tailings located at the bottom of the mud layer expedite the precipitation of interstitial water within the floc structure through the combined influence of gravity and rake frame shear. Consequently, a denser floc structure forms, as evidenced by a higher concentration of bottom flow at a macroscopic level. This conclusion provides a theoretical basis for faster preparation of highly concentrated tailings slurry in CPB.

The purpose of this study was to investigate the effect of the use of rubber powder from tire recovery on the dynamic loading performance of CPB. Finally, it is concluded that using recycled rubber material to backfill mine paste is helpful in reducing waste tire pollution and improving the impact resistance of the backfill body. The dynamic compressive strength, Dynamic Increase Factor (DIF), peak dynamic load strain, and dynamic load elastic modulus of the samples composed of slag, Portland cement, wastewater, and rubber powder were determined. Through the analysis of the experimental data, it can be seen that the recycled rubber reduces the dynamic compressive strength and DIF of the specimen but increases the peak dynamic load strain and dynamic load elastic modulus and other characteristics, and enhances the ability of the filled body to absorb elastic strain energy. The results show that recycled rubber can increase the deformation ability of the filler and improve the impact resistance of the filler. The results of this study provide valuable information and industrial applications for the effective management of solid waste based on sustainable development and the circular economy.

Macroscopic and microscopic properties of cemented paste backfill (CPB) were studied through uniaxial compressive testing, acoustic emission (AE) monitoring, and microscopic feature analysis. The research shows that the uniaxial compressive strength (UCS) and elastic modulus have an exponential function type positive correlation with the increase in curing time and a polynomial function type with the rise of curing temperature; the mechanical parameters reach the maximum when the curing temperature is 40 °C. Increasing the curing time and curing temperature can promote the transition from shear crack to tensile crack. Increasing the curing time and raising the curing temperature both promote the transition of shear crack to tensile crack in the CPB. Overall, the crack mode is a combination of tensile and shear crack. At room temperature, the shear cracks dominates in the initial stage, but the proportion of the shear cracks decreases as the pressure increases in uniaxial compression test. At a curing temperature of 60 °C, the crack mode transitions to a tensile-shear mixed crack, with tension becoming the dominant crack mode. Microscopic analysis suggests an excellent linear correlation between the pore fractal dimension, UCS, and elastic modulus. When the pore fractal dimension decreases, the mechanical parameters also decrease. The pore fractal dimension can effectively characterize the macroscopic mechanical properties. Finally, the curing temperature is divided into two stages, with 40 °C as the dividing line for analysis. In the first stage, the increase in curing temperature effectively improved the mechanical parameters; in the second stage, the excessively high hydration reaction rate weakened the mechanical parameters.

Cemented paste backfill (CPB) has been a practical approach for mining waste management, underground goaf treatment, and green mining. Strength deterioration because of high sulfide content (SC) is a severe challenge for sulfide-rich CPB. To investigate the influence of rice straw (RS) on the strength of sulfide-rich CPB, RS was utilized as an inhibitor of strength deterioration. RS dosage (RSD), RS length (RSL), and sulfide content (SC) were chosen as the factors, and two stages of the experiment were carried out. It was found that high SC produced pores, cracks, and loose microstructure of CPB, resulting in the strength deterioration of sulfide-rich CPB. The 90-day uniaxial compressive strength (90 d-UCS) was the maximum of the UCS of sulfide-rich CPB. The hydration products and microstructural characteristics observed by XRD and scanning electron microscopy (SEM) illustrated that RS has the effect of bridging and water retention. Accordingly, adding RS improved the long-term strength of sulfide-rich CPB. The optimal RSD, RSL, and SC for 90 d-UCS of sulfide-rich CPB were obtained through the response surface methodology approach. The optimal conditions within the experimental range of this study for maximum 90 d-UCS of CPB with high SC (17 wt%) were RSD of 0.032 wt% and RSL of 0.28 cm, producing a 90 d-UCS of 5.14 MPa.

To solve the disposal problems of carbide slag (CS), soda residue (SR), and red mud (RM) solid wastes, a new type of cemented paste backfill (CPB) was prepared with CS, SR, and RM solid wastes. The mixing proportion for the CPB was optimized by combining the Box‒Behnken design (BBD) response surface method and the satisfaction function method. The strength formation mechanism for the CPB was analyzed with physical and mechanical property tests, X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), etc. The safety of the CPB was evaluated with heavy metal leaching testing. The results showed that the 28-day unconfined compressive strength (UCS) of CPB first increased and then decreased with increasing CS/RM (0.2 ~ 0.6) and SR/RM (0.2 ~ 0.6); the optimum mixing ratios were CS/RM = 0.45 and SR/RM = 0.37, and the solid mass concentration was 64.75%; dense calcium silicate (aluminum) hydrate (C-S–H/C-A-S–H) bound to the solid particles of red mud and filled pores to provide early strength for the CPB, laminar interwoven Friedel's salt (Fs), ettringite and portlandite hydration products provided late strength for the CPB; and the leaching concentrations of five heavy metals (Fe, Mn, Cu, Zn, and Cr) in the solidified CPB were greatly reduced and far below the leaching limits specified in China's Quality Standard for Groundwater (GB/T 14848–2017). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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In Peru, socio-environmental conflicts related to the development of mining-metallurgical processes and the responsible disposal of mine tailings have become central issues for accepting mining projects, especially regarding building relationships of trust with the communities. This condition has prompted the Peruvian mining industry to advance in managing alternatives to the conventional surface disposal of mine tailings. A promising and increasingly popular management strategy for mine tailings in Peru is their disposal inside underground mines. This article presents: site-specific conditions, advantages/disadvantages, and lessons learned from practical experiences of mine tailings disposal in underground mines in Peru. In addition, some techniques are highlighted, such as (i) hydraulic fill, (ii) cemented hydraulic fill, and (iii) cemented paste backfill. Finally, this article concludes that the responsible disposal of mine tailings in underground mines is a green mining solution that reduces negative socio-environmental impacts, limiting the generation of acid rock drainage (ARD) and the leaching of metals due to the decrease in contact with oxygen and rainfall, thus mitigating the contamination of surface and underground waters, reducing the footprint of affectation in the territory, and eliminating the emission of particulate matter in the environment. [ABSTRACT FROM AUTHOR]