Paste Backfill Research Articles

Synthesis of cemented paste backfill by reutilizing multiple industrial waste residues and ultrafine tailings: Strength, microstructure, and GA-GPR prediction modeling

Industrial waste residues are increasingly reutilized in the preparation of cemented paste backfill for reducing the cost of mine filling. Therefore, to promote the utilization of the bulk industrial waste residues (IWRs), mechanical and microstructure properties of cemented ultrafine tailings backfill (CUFTB) manufactured by reutilizing 5–10 wt% steel slag (SS), 5–10 wt% fly ash (FA), 16–22 wt% carbide slag (CS), 0–3 wt% desulfuration gypsum (DG), and 40–74 wt% blast furnace slag (BFS) and ultrafine tailing (d50 = 10.84 μm) were investigated after curing of 1-, 3-, 7-, 14-, 28-, 56- days. Unconfined compressive strength (UCS) test was adopted to determine strength and the regression analysis was applied to establish UCS prediction model. XRD, SEM, and MIP were used to evaluate the evolution characteristics of CUFTB microstructure. The obtained results indicate that the cementitious material synthetized by IWRs can completely substitute Portland Cement (PC) for CUFTB. After curing of 28 days, CUFTB exhibit UCS values with increasing of 10.80% ∼ 44.89% than those made of PC. Logarithmic function UCS=α⋅lnt+β is constructed to characterize UCS development with curing time. By optimizing the hyperparameters of Gaussian process regression (GPR) using Genetic algorithm (GA), GA-GPR model is established with high accuracy for predicting UCS. Microscopic analysis reveals that under the alkaline environment, the hydration reaction of SS, FA, BFS occurred to generate calcite (CaCO3), ettringite (AFt) and hydrate calcium silicate gel with a low Ca/Si ratio. Microtopography formed with more refined pore distribution of 0.003- and 1- μm inside CUFTB. To substitute PC using the cementitious material synthesized by IWRs can reduce the mining cost and CO2 emission. The findings provide the guidance for the synthesis of sustainable filling material by reutilizing IWRs.

Improving early-age performance of alkali-activated slag paste backfill with calcium salts at low temperature

The hydration of alkali-activated slag (AAS) is highly sensitive to the curing temperature, especially at early ages. In low temperature environment, cemented paste backfill made of AAS (AAS-CPB) exhibits notably reduced early-age uniaxial compressive strength (UCS), attributable to the inhibitory effect of low temperature on slag hydration. This study aims to improve the performance of AAS-CPB at low temperatures by incorporating chemical additives. The results shows that calcium salts, specifically CaCl2, CaSO4, and Ca(COOCH3)2, can increase the early-age UCS of AAS-CPB by up to 1050%, depending on the specific anion involved. Overall, CaCl2 provides the greatest enhancement in the UCS. However, the presence of these salts result in strength degradation at later ages. A pronounced exponential relationship is evident between UCS and ultrasonic pulse velocity. The change of conductivity and moisture content are valuable indicators of hydration process at low temperatures. C(N)-A-S-H, hydrotalcite and portlandite are the primary hydration products. Anions play a decisive role in the morphology, precipitation and quantity of C(N)-A-S-H. The slag hydration degree and UCS basically exhibit a consistent trend.

Energy evolution and mechanical properties of modified magnesium slag-based backfill materials at different curing temperatures

To study the mechanical properties and failure characteristics of all-solid waste cementitious materials prepared in the intense geothermal environment of deep mines. Uniaxial compression, acoustic emission (AE), SEM and other tests were adopted to characterize the energy and deformation failure of backfill materials from different temperatures (20 °C, 30 °C, 40 °C). The results show that the temperature has a promoting effect on the development of modified magnesium slag-fly ash cemented paste backfill (MFPB) strength. The elastic strain energy and the dissipated energy corresponding to the peak stress increase as the curing temperature increases. The high frequency phase of the energy scatter plot is accompanied by a rapid increase in the cumulative ringing count and cumulative energy. Tensile cracks increase with the increase of curing temperature. The temperature effectively promotes the hydration process of MFPB. The decrease of strength in the later stage of curing temperature 40 °C is due to the harmful thermal stress within the backfill. The results provide theoretical guidance for the practical application of MFPB.

Impact of Admixtures on Environmental Footprint, Rheological and Mechanical Properties of LC3 Cemented Paste Backfill Systems

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.

Mitigating Risks in Coal Mining: Simulation-Based Strategy for Oxidation Zone Control Using Inorganic Paste Backfill at the Working Face Corners

Insufficient stability of the top plate at the corner of an easily combustible coal seam comprehensive mining face may lead to a natural fire within the goaf. While corner sealing is crucial for minimizing air leakage, current sealing methods struggle to effectively prevent such leakage. Additionally, the distribution characteristics of the oxidation zone in the goaf after sealing are unclear, making it difficult to control the extent of the oxidation zone. To address these issues, a new type of inorganic paste filling material was developed, taking into account the conditions of the Cuncaota II Mine. Various corner-filling schemes were developed, and numerical simulations were used to study the effects of different corner-filling strategies and varying filling interval distances on the width of the oxidation zone in the goaf. Based on these findings, a working face corner-filling technology was proposed and applied to the 22,122 working face. The research results indicate that the mountain sand-based paste filling material, using mountain sand as the filling aggregate and cement and fly ash as the binding materials, not only meets the pumping requirements but also exhibits excellent self-supporting characteristics, thereby addressing the corner filling needs of the working face. The width variation in the oxidation zone in the goaf is influenced by the position and interval distance of the corner filling, showing a pattern of initially decreasing and then increasing with the rise in the filling interval distance, reaching a minimum at a filling interval of 50 m. Field observation data demonstrate that, following the application of the aforementioned filling technology, the width of the oxidation zone in the goaf of the 22,122 working face is reduced by 37.5%, and air leakage decreases by 66.7% compared to the unfilled condition. This technology effectively narrows the range of the oxidation zone in the goaf, ensuring the safety of working face production.

Ultrasonic and Microstructural Evaluation of Sulphide-Rich Tailings Cemented Paste Backfill Properties Containing Alkali-Activated Slag: Effect of Slag Fineness

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.

Effect of roughness on shear behavior of interface between cemented paste backfill and rock

The interaction between cemented paste backfill (CPB) and rock at their interface plays a crucial role in the stability of underground backfill structures. Considering the interface roughness could have a significant influence on the shear behavior and mechanical properties of the interface, a series of laboratory direct shear tests were carried out on the CPB-rock interface with various roughnesses. The results indicates that the interface roughness and normal stresses have a remarkable effect on the interfacial shear behavior, with typical stress-shear displacement curves that could be classified into three types depending on the peak and post-peak characteristics. Compared to the smooth interface, the shear strength increases with increasing roughness, owing to the enhancing interlocking effect, which is confirmed by digital image correlation (DIC) in micro views. In addition, the shear contraction observed at the smooth interface changes to shear dilatation at the rough interface, which is caused by wider distribution and higher adhesion of CPB asperities, as observes by using 3D laser scanning technology. Furthermore, a theoretical model for the shear strength, taking into account the influence of interface roughness, is developed to assess its effect on shear strength. The experimental results and the theoretical model presented in this paper will contribute to better understand the interaction mechanism and predict the shear strength of the interface.

Study of fresh properties of cemented paste backfill material with ternary cement blends

This study is aimed at evaluating the effects of ternary blended Portland cement type I (PCI) with slag and limestone (LS) powder on key engineering fresh properties of CPB: (i) rheological properties and (ii) setting time. CPB samples with PCI/Slag ratios of 50/50 (Group A) and 80/20 (Group B) were considered in this study. The effect of LS in the ternary mix was investigated by replacing the slag with increasing doses of LS (5, 10, and 20 wt%). The specimens were cast and cured over periods of 0, 0.25, 1, 2 and 4 h and tested for rheological properties (yield stress, viscosity). In addition, tests were performed to identify the initial and final setting time of the samples. In addition, microstructural tests, zeta potential and pH measurements, and monitoring experiments (temperature, electrical conductivity) were carried out to better comprehend the underlying mechanisms behind the observed changes in rheological behavior and setting time. The findings have shown that the replacement of slag by a higher dosage of LS in the ternary binder significantly affects the rheological properties of the studied CPB. It reduces the yield stress and increases the viscosity of CPB. The effect of LS on the rheological properties of CPB is mainly attributed to the physical (e.g., filler effect, lubrication, particle size) and chemical (nucleation and changes in repulsive forces between CPB particles) effects of LS in the ternary system. The findings also revealed that increasing the proportion of limestone in the CPB ternary binder system prolonged the setting time (initial and final) of the CPB mixture due to the nucleation and dilution effects of LS. Overall, the synergy between slag and LS was observed; the optimal use of LS and slag in the ternary system can serve as a sustainable alternative to the predominantly used ordinary Portland cement (OPC) or OPC/Slag binary binder, thereby reducing the energy consumption and carbon footprint associated with cement and CPB technology. The results of this research will be valuable for a better comprehension of the impacts of ternary binder with an increasing percentage of LS on the rheology and setting time of the CPB mix, ultimately, the efficient design of the mixing plant, especially the backfill transportation system.

Preparation and strength formation mechanism of alkali-stimulated spontaneous combustion gangue-granulated blast furnace slag backfill.

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.

A New index and control method of filling effect for cemented paste backfill in coal mines

ABSTRACT 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.

Wear characteristics of the pipeline transporting cemented paste backfill containing coarse aggregate

Cemented paste backfill (CPB) offers unique advantages for managing tailings and underground mining voids, sometimes incorporating coarse aggregate. The pipeline is crucial for transporting CPB that contains coarse aggregate (CPBC), and excessive wear can compromise safety and continuity of transportation. However, the wear characteristics of the pipeline that transports CPBC are not well understood. In this study, wear tests were conducted using a novel self-designed instrument to investigate the impact of CPBC mass fraction (76–84%), flow velocity (1.0–2.5 m/s), coarse aggregate content (0–35%), and coarse aggregate particle size (1.05–7.34 mm). The results indicate that the wear rate increases in a power-law manner with both flow velocity and the size of coarse aggregate particles. The wear rate exhibits a non-monotonic trend with increasing CPBC concentration, initially rising, then declining before sharply increasing. With an increase in coarse aggregate content, the wear rate initially decreases slowly and then increases rapidly. The inflection point in the wear rate is associated with the interconversion between abrasion and erosion, which is governed by the yield stress of CPBC. Given the same material composition and wear type, and minimal variation in aggregate particle size, a higher yield stress of CPBC results in a higher wear rate. Abrasion and erosion dominate the total wear, contributing an average of 71.3%. The findings facilitate the selection of CPBC recipes and pipe materials to mitigate excessive pipe wear, while also providing significant potential for predicting pipe wear based on yield stress of paste.

Mechanical behaviors of backfill-rock composites: Physical shear test and back-analysis

The shear behavior of backfill-rock composites is crucial for mine safety and the management of surface subsidence. For exposing the shear failure mechanism of backfill-rock composites, we conducted shear tests on backfill-rock composites under three constant normal loads, compared with the unfilled rock. To investigate the macro- and meso-failure characteristics of the samples in the shear tests, the cracking behavior of samples was recorded by a high-speed camera and acoustic emission monitoring. In parallel with the experimental test, the numerical models of backfill-rock composites and unfilled rock were established using the discrete element method to analyze the continuous-discontinuous shearing process. Based on the damage mechanics and statistics, a novel shear constitutive model was proposed to describe mechanical behavior. The results show that backfill-rock composites had a special bimodal phenomenon of shearing load-deformation curve, i.e. the first shearing peak corresponded to rock break and the second shearing peak induced by the broken of aeolian sand-cement/fly ash paste backfill. Moreover, the shearing characteristic curves of the backfill-rock composites could be roughly divided into four stages, i.e. the shear failure of the specimens experienced: stage I: stress concentration; stage II: crack propagation; stage III: crack coalescence; stage IV: shearing friction. The numerical simulation shows that the existence of aeolian sand-cement/fly ash paste backfill inevitably altered the coalescence type and failure mode of the specimens and had a strengthening effect on the shear strength of backfill-rock composites. Based on damage mechanics and statistics, a shear constitutive model was proposed to describe the shear fracture characteristics of specimens, especially the bimodal phenomenon. Finally, the micro- and meso-mechanisms of shear failure were discussed by combining the micro-test and numerical results. The research can advance the better understanding of the shear behavior of backfill-rock composites and contribute to the safety of mining engineering.

Damage characterization and microscopic mechanism of steel slag-cemented paste backfill under uniaxial compression

The utilization of steel slag-cemented iron tailings for preparing mine backfill materials can effectively consume industrial solid waste generated from steel production and significantly reduce backfilling costs. The study analyzed the influence and mechanisms of steel slag (SS) content on the mechanical damage characterization of steel slag-cemented paste backfill (SS-CPB) through uniaxial compressive strength (UCS) tests and microscopic testing methods such as X-ray diffraction (XRD) and a scanning electron microscope (SEM). The engineering applicability and economic feasibility of the material were evaluated. The main conclusions were as follows: (1) With the increase of SS content, the strength of SS-CPB first increases and then decreases, with the highest strength observed at a 10% SS content. (2) The inclusion of SS in SS-CPB leads to higher peak strain and post-peak strength, demonstrating significant plastic deformation characteristics. (3) When the SS content increases from 30% to 60%, the Ca(OH)2 content in SS-CPB hydration products decreases by 20.2%, and internal micropores increase. (4) When the SS content reaches 30%, the damage mode of SS-CPB changes from purely splitting failure to a plastic combination of splitting and shear failure. These research findings provide a new application model for the collaborative utilization of steel slag, tailings, and other solid wastes.

Effect of Alkali-Activated Slag and Phosphogypsum Binder on the Strength and Workability of Cemented Paste Backfill and Its Environmental Impact

Effect of Alkali-Activated Slag and Phosphogypsum Binder on the Strength and Workability of Cemented Paste Backfill and Its Environmental Impact

Effect of temperature-rising inhibitor on the hydration and performance of cemented paste-filling material

The addition of a temperature-rising inhibitor (TRI) to aeolian sand paste materials (ASPM) to produce paste-like filling mining materials can solve multiple problems. First, it may alleviate the environmental problems caused by solid waste treatment in mines to achieve sustainable use of solid waste. Second, It may solve the problem of rapid temperature rise in mines caused by the rapid heat release during filling body hydration. Therefore, this study explored the hydration of an ASPM with different TRI contents and its mechanical properties, setting time, and microstructure. The results show that at TRI contents of 0–1.0%, the peak heat-release rate of the ASPM is reduced by 16.0%, the early hydration heat release is reduced by 14.2%, and the delay of the heat-release peak is more prominent. TRI inhibits the hydration of ASPM primarily within 7 d, which reduces the early strength of the ASPM by a maximum of 43.4%. However, with the increase in age, the strength difference gradually decreases, and TRI even becomes beneficial for the development of strength in later stages. In addition, the high content of TRI has a significant retarding effect on ASPM hydration. The temperature rise test shows that TRI can reduce the temperature increase rate and delay the peak temperature increase rate, which can effectively solve the problem of concentrated heat release by backfill. This paper provides a theoretical basis for the application of TRIs in cemented paste backfill.

A machine learning model to predict unconfined compressive strength of alkali-activated slag-based cemented paste backfill

A machine learning model to predict unconfined compressive strength of alkali-activated slag-based cemented paste backfill

Experimental Development of an Innovative Approach to Enhance the Strength of Early Age Cemented Paste Backfill: A Preliminary Investigation of Microwave-Assisted Curing

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.

Deeper Understanding of the Strength Evolution and Deformation Characteristics of Sodium Silicate–Cemented Paste Tailing Material

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.

Co-treatment of steel slag and oil shale waste in cemented paste backfill: Evaluation of fresh properties, microstructure, and heavy metals immobilization

The environmentally sustainable treatment of steel slag (SS) and oil shale waste (OSW) is a significant concern in the field of industrial development. The mining industry also faces challenges related to the high costs and carbon emissions associated with ordinary Portland cement (OPC), leading to environmental pollution. To address these challenges, this study aimed to develop a cost-effective and environmentally friendly binder for cemented paste backfill (CPB) by utilizing SS and calcined oil shale waste (COSW) as primary precursors. Extensive investigations were conducted to evaluate the properties of the CPB sample with varying COSW content, including rheological properties, mechanical strength, and microstructure. The binder sample was comprehensively characterized using isothermal calorimetric analysis, X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscopy (SEM). Based on systematic experimentation, an optimal blend ratio for the binder was determined, consisting of 60 wt% SS, 15 wt% COSW, 15 wt% phosphogypsum (PG), and 10 wt% OPC. The exceptional performance of the binder was attributed to the substantial formation of precipitated ettringite (AFt), resulting in a more compact structure and improved mechanical strength. Additionally, a sequential extraction test revealed that the heavy metals in the CPB sample were mainly present in the residual fraction, demonstrating the effective immobilization of heavy metals by the binder.

Effect of submerged curing on properties of cemented paste backfill

ABSTRACT 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.