Strength Of Backfill Research Articles

Optimization of Proportions of Alkali-Activated Slag-Fly Ash-Based Cemented Tailings Backfill and Its Strength Characteristics and Microstructure under Combined Action of Dry-Wet and Freeze-Thaw Cycles.

To enhance the application of alkali-activated materials in mine filling, cemented tailings backfill was prepared using slag, fly ash, sodium silicate, and NaOH as primary constituents. The effects of the raw material type and dosage on the backfill were examined through a single-factor experiment. Additionally, response surface methodology (RSM) was utilized to optimize the mixing ratios of the backfill, with a focus on fluidity and compressive strength as key objectives. The evolution of backfill quality and compressive strength under the combined effects of dry-wet and freeze-thaw (DW-FT) cycles was analyzed. The hydration products, microstructure, and pore characteristics of the specimens were analyzed using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and nitrogen adsorption tests (NATs) across varying cycles. The results demonstrate that the optimal backfill composition includes 47.8% fly ash, 6.10% alkali equivalent, and a 1.44 sodium silicate modulus. The macroscopic behavior of the backfill under DW-FT coupling followed this progression: pore initiation → pore expansion → crack formation → crack propagation → structural damage. After a minor initial increase, the backfill strength steadily decreased. Microscopic analysis revealed that the decline in internal cementation products and the deterioration of pore structure were the primary causes of this strength reduction. Thus, the DW-FT coupling can cause significant erosion of the backfill. The technical solutions presented in this paper offer a reference for solid waste utilization and provide valuable insights into the durability of backfill under DW-FT coupling.

Cementation characteristics and hydration mechanism of magnesium slag-phosphogypsum composite cementitious materials

The selection and mixing proportion of cementitious materials in cemented backfills are of great engineering importance to ensure the quality of the backfill. Therefore, based on the mixing proportion test of magnesium slag-phosphogypsum composite cementitious materials, the strength change characteristics and volume change rate of the cemented backfill under different cementitious material proportions were investigated. Combined with indoor tests such as hydration heat test, X-ray diffraction, thermogravimetric-differential thermogravimetric, scanning electron microscopy, and mercury intrusion porosimetry, the hydration mechanism of the cemented backfill under different cementitious material proportions was investigated. The results showed that the highest strength of the cemented backfill was observed with only magnesium slag as the activator. The strength of magnesium slag-phosphogypsum and magnesium slag-desulfurized gypsum cemented backfill was greater than that of cement cemented backfill, yet lower than that of magnesium slag alone cemented backfill. The shrinkage trend and magnitude of magnesium slag alone excites blast furnace slag cemented backfill and cement cemented backfill were similar. With the increasing content of phosphogypsum and desulfurized gypsum, the shrinkage of the backfill tended to increase, especially when the content was 18%. The gel-like products of backfill with magnesium slag-based cementitious materials increased rapidly at 7 days, which strongly bonded the aggregates and filled the backfill pores, resulting in high backfill strength. Although the porosity of backfill with magnesium slag-based cementitious material showed an increasing trend with the increase of age, its most available pore size decreased and harmful pores became less. The results can provide a reference for the application of magnesium slag-phosphogypsum composite cementitious materials.

Delving into the role of microwave curing on the strength and cement hydration features of cemented tailings backfill

Cemented tailings backfill (CTB) comprises tailings, binders, and water and is filled into goaves to regulate the ground pressure and ensure production safety. Thus, shortening the curing time of CTB has been a popular research topic in backfill mining as it maximizes the extraction of the neighboring stopes while lowering mining-related costs. In this study, a self-made horn microwave experimental device was developed to rapidly enhance CTB’s strength property. Subsequently, the microwave-curing effects on the upper surface temperature, strength, deformation coefficient, and hydration reaction of CTB were explored through uniaxial compressive strength, X-ray diffraction, and thermogravimetric/differential thermogravimetric experiments. Experimental marks revealed that the strength property of early-aged (up to 7 d) CTB composites could be rapidly enhanced by microwave curing, except for the 7-d-cured fills with microwave curing times of 5–7 min. Moreover, the hydration reactions of CTB after 3- and 7-d curing were substantially accelerated by microwave curing. Thus, this study offers a novel method of satisfactorily increasing early-aged CTB strength and exploring its hydration mechanisms effectively.

Improvement of Fluidity and Long-term Strength of Cemented Paste Backfill with Low Calcium Fly-ash

ABSTRACT Waste rocks and tailings are widely applied materials in underground metal mines to backfill mined-out areas. To test the effect of low calcium fly ash on slurry fluidity and long-term strength of cemented paste backfill, orthogonal experiments of backfill proportions with variable levels of waste, tailing, fly ash, water and their combinations were carried out. Results show that slurry slump is most sensitive to mass concentration, and slurry fluidity is optimal when fly ash-cement ration is 1:1. The longterm strength of cemented paste backfill after curing for 56 days is significantly affected by cement-(tailing + waste) ratio, and slightly evolves regardless of fly ash-cement ratio. Fly ash promotes the generation of active silicon oxide and aluminum oxide, which fills the pores within the backfill. The optimal proportion of cemented paste backfill is 77% mass concentration, 8:2 tailing–waste ratio, 1:30 cement-(tailing + waste) ratio and 1:1 fly ash–cement ratio. The correlative slurry slump and long-term backfill strength meet the requirement of pumping and backfill mining. Additionally, an industrial scale loop pumping test of backfill slurry shows the pipeline transportation resistance is 4 kPa/m, pipeline diameter is optimal at 150 mm, and flow rate is optimal at 90–100 m3/h. The experiment confirms that proper addition of low calcium fly ash is conducive to improve the slurry fluidity and long-term strength of cemented paste backfill.

Prediction model of maximum stress for concrete pipes based on XGBoost-PSO algorithm

Due to varying burial conditions and service environments, concrete pipes exhibit complex mechanical behavior. Existing theoretical, simulation, and test methods for determining the maximum stress of pipes have significant limitations, including excessive assumptions, low efficiency, and restricted applicable conditions. Therefore, there is an urgent need to propose a multi-factor associated method for pipe stress prediction. This paper proposed an innovative approach to finely simulate the mechanics response for concrete pipes under the coupling action of stress-seepage-fluid fields. The accuracy of this numerical simulation method was validated through full-scale test. Sensitivity analysis based on Morris sensitivity analysis theory was conducted on traffic load magnitude and speed, buried depth, groundwater table, fluid height and velocity, bedding strength, backfill strength, and pipe diameter. A dataset of “physical variables - maximum stress” for concrete pipes was established. A multi-factor-correlated prediction model of maximum stress for concrete pipe was proposed using XGBoost machine learning method optimized by Particle Swarm Optimization (PSO) algorithm. The results indicate that pipe diameter is highly sensitive; buried depth and traffic load magnitude are sensitive; groundwater table, bedding strength, and backfill strength are moderately sensitive; while fluid height, traffic speed, and flow velocity are insensitive. The XGBoost-PSO model demonstrates the highest accuracy and lowest error compared to BP, RF, and XGBoost models, with improvements in prediction accuracy of 59.6 %, 23.8 %, and 8.6 %, respectively. The model achieves RMSE of 0.118 and MAE of 0.213, demonstrating the suitability of the XGBoost-PSO model for predicting maximum stress for concrete pipes.

Effects of superabsorbent polymer on mechanical properties of cemented paste backfill and its mechanism evolution

Cemented paste backfill (CPB) technology offers advantages in safety, efficiency, environmental protection, and economy, and it has been increasingly applied in mines worldwide. The mechanical properties of CPB are critical indicators of the quality of the backfill. Traditionally, cement is used as the primary binding material; however, its high cost and the resulting inconsistent strength of CPB present challenges. Superabsorbent polymer (SAP) has been extensively used in cement-based materials due to its beneficial effects on mechanical properties, shrinkage, and durability. In this study, SAP is incorporated as an additive, with the unclassified tailings from an iron ore mine used as the research material to prepare SAP-enhanced CPB. The study focuses on SAP content, the cement-to-tailings ratio, and curing time as the main influencing factors. Uniaxial compressive strength (UCS) tests, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests were conducted on CPB specimens to investigate the mechanical characteristics of SAP-enhanced CPB and to explore the influencing mechanisms of SAP on CPB. The results indicate that CPB strength initially increases and then decreases with rising SAP content, reaching a maximum UCS value at 0.2 % SAP content. XRD, TGA, and SEM results show that SAP affects the formation of hydration products and the pore structure of CPB. Specifically, when the SAP content is below 0.2 %, increasing SAP content leads to a denser pore structure and lower porosity, which correlates with higher UCS values. There is an exponential decrease in UCS with increasing porosity. Additionally, a quadratic relationship exists between UCS and the amount of calcium hydroxide, a key hydration product in CPB specimens. These findings provide valuable insights for improving the mechanical properties of CPB and serve as a reference for designing the strength of backfill in similar mining applications.

Management Solutions and Stabilization of a Pre-Existing Concealed Goaf Underneath an Open-Pit Slope

Pre-existing concealed goafs underneath open-pit slopes (PCO-goafs) pose a serious threat to the stability of open-pit slopes (OP-slopes), which is a common problem worldwide. In this paper, the variable weight-target approaching method, equilibrium beam theory, Pratt’s arch theory, and numerical simulation are used to analyze the management solutions and stability of five PCO-goaf groups in the Nannihu molybdenum mine located in Luoyang City, Henan Province, China. The five PCO-goaf groups, numbered 1#, 2#, 3#, 4#, and 5#, are divided into four hazard classes, ranging from extremely poor to good stability. The stability of 1#, 2#, and 4# is poor and must be managed by filling, and the design strength of backfill is 1.2 MPa; caving is used to treat 3# and 5#, and the safe thickness of the overlying roof is calculated to be 10.5–41 m. After treatment, the safety coefficient of the slope is greater than 1.2, indicating that the slope is stable. This study provides insight and guidance for the safe operation of open-pit mines threatened by the existence of PCO-goafs.

Numerical investigations of GRS wall performance with tiered configurations

Geosynthetic Reinforced Soil (GRS) walls have become increasingly popular as a result of their numerous advantages. In some cases these structures are constructed in a multi-tiered configuration, which makes their behavior more complicated. Nevertheless, the response of the multi-tiered walls is insufficiently explained by the existing design manuals and literature studies. This paper investigated the performance of GRS walls with multi-tiered configurations using two-dimensional (2D) finite element numerical models. This study compares the performance of two-tiered GRS walls with simple GRS walls (single-tiered). It also examines the impact of offset distance, backfill strength properties, and reinforcement parameters (vertical spacing and reinforcement length) on horizontal deformations and reinforcement tensile loads in two-tiered GRS walls. Adopting a multi-tiered configuration for GRS walls can significantly reduce both the horizontal wall deformation and the maximum reinforcement tensile loads. Additionally, the critical offset distance found in this study is significantly smaller than that recommended by the Federal Highway Administration (FHWA) guidelines. The finite element results also demonstrate that using high-quality backfill soil can minimize interaction between lower and upper tiers. Using a uniform reinforcement length of 0.6H for both tiers significantly reduces horizontal deformation compared to the FHWA recommendation of 0.6H and 0.35H for the lower and the upper tier respectively.

Study of Slope Stability of the Mining Wall in an Open-Pit Coal Mine by the Paste Cut-and-Backfill Method

According to this study’s findings, slope stability problems in open-pit coal mines can be avoided, and mine wall collapse can be effectively mitigated by the use of cut-and-backfill mining techniques. The main research results are as follows: (1) The stope and waste rock’s geotechnical, physical, and mechanical characteristics were gathered and examined; the geotechnical and mechanical characteristics found in this study largely satisfy the criteria for slope stability analysis. (2) Cemented paste backfill (CPB) materials were made of mine waste rock and fly ash at a desired ratio, mixed with cement as a bond material, and were tested in the laboratory, using a combination of cement percentages of 6%, 8%, and 10% for the cement content and 25%, 30%, 35%, and 40% for the fly ash content, to determine the ideal mix for artificial ground support in underground mines, taking into account both economic and performance factors. (3) By using this model, the changes in CPB strength were investigated under various factors influencing the cement ratio, and limit equilibrium modeling was used with the FLAC-Slope 8.1 program with different cement paste backfill ratio to calculate the factor of safety for each cement percentage after 1 day, 3 days, 7 days, and 28 days of curing time (CT) to obtain the optimum compressive strength and shear straight of cemented paste backfill with high paste fill shear strength on the slope. (4) The research results are of great significance for the safety of important facilities in open-pit mines and provide a basis for the design and safety implementation of open-pit slope engineering.

Effect and mechanism of time-dependent and economical expansion materials in improving the active roof-contact for cemented paste backfill

During the backfilling process, there is often a problem of no roof-contact, and the time and state of roof-contact cannot be predicted, seriously affecting the backfilling safety and efficiency. Therefore, the expansion effect, mechanism, and time dependence of the expansion agents used to achieve roof-contact were studied through expansion ratio tests, strength tests, and microscopic analysis. The expansion ratio of the MgO-type expansion agent (MEA) can meet the requirement of backfilling, and the unconfined compressive strength (UCS) of the expansive cemented paste backfill (ECPB) was attenuated compared to that of ordinary cemented paste backfill (CPB). Through scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) of the MgO-type ECPB, it is found that the ECB produces Mg(OH)2 crystals, which improves the compensation space inside the ECPB. MIP analysis results also show that the ECPB has higher porosity and more macropores, which is the reason for the strength attenuation of the ECPB. It is found that the expansion ratio and sedimentation ratio of fresh ECPB are time-dependent, and they both conform to logarithmic function. Afterwards, through the dynamic relationship between the sedimentation and expansion of fresh ECPB, the synthetic criterion of roof-contact based on the time-dependent model of expansion ratio and sedimentation ratio was established. The theoretical shortest roof-contact time of different experimental groups was obtained. Finally, through a comparative analysis of backfilling costs, the lowest cost and reasonable backfilling scheme were obtained. It is of great value for judging the effectiveness of roof contact, optimizing the backfilling proportion scheme, ensuring backfilling safety, and saving backfilling and mining costs.

Analysis of physical characteristics and mechanism of retarder to stratified cemented backfill

The stratified structural plane caused by stratified backfill will reduce the strength of backfill, and the introduction of retarder will make up for the defect. Three retarders, sodium tripoly-phosphate, citric acid and sucrose, were introduced. After determining the optimal dosage of retarder, they were added into the filling slurry with a ratio of lime to sand of 1:6 and a mass concentration of 75%. Based on the hydration reaction mechanism and damage mechanics theory of cement, the setting time test and uniaxial compressive strength test were carried out. With the help of scanning electron microscopy and X-ray diffraction, the influence mechanism of retarder on the physical characteristics of stratified cemented filling was investigated.The main research contents and achievements are as follows:. The results showed that the three retarding agents can delay the setting time of the cement filling slurry, and the retarding effect is sucrose > citric acid > sodium tripolyphosphate. The addition of retarder can improve the uniaxial compressive strength and integrity of stratified consolidated backfill, and the best filling interval time (FIT) is 12 h. Appropriate addition of retarder will increase the amount of cement hydration products, make the structure of hydration products more dense, reduce the formation of stratified structural plane, and help to improve the strength of stratified cemented backfill.

Strength and Crack Propagation Analysis of Layered Backfill Based on Energy Theory

The strength of backfill is greatly influenced by its inclination angle and interlayer concentration. In order to study the influence of inclination angle and interlayer mass concentration on the strength of backfill, a group of layered cemented backfill with cement-sand ratio of 1:4, interlayer mass concentration of 66%, 67% and 68% and inclination angles of 0°, 10°, 20° and 30° were prepared by using tailings as aggregate. The uniaxial compression test was carried out to analyse the effect of interlayer mass concentration and inclination angle on layered cemented backfill. The crack propagation and energy change law of the specimen during compression were analysed by J-integral and energy conservation law. The relationship between the crack initiation and propagation and strain energy of two representative three-layer backfill specimens was analysed by numerical modelling. The results show that the increase in the layer number and the inclination angle of the backfill can weaken the strength of the backfill. In a certain range of inclination angles, the weakening coefficient of the backfill caused by the inclination angle is very consistent with the cosine value of the corresponding angle. Due to the release of crack energy and the existence of interface J integral, the uniaxial compressive strength of different mass concentration backfill is different at various positions. When the displacement reaches a certain value, the crack and strain energy no longer increase.

Enhancing performance and structural integrity of cemented paste backfill: Rheological behavior, strength characteristics, and microstructural dynamics

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.

Upper bound stability analysis of tiered geosynthetic-reinforced soil wall

The tiered geosynthetic-reinforced soil (GRS) walls have been increasingly applied in the high and steep retaining soil structures. However, very little is known about the design method for the tiered GRS wall in practice. This study is aimed at proposing an upper-bound stability analysis method of a tiered GRS wall. The proposed method was firstly validated by the existing results from the centrifuge test and the numerical method, and then a parametric study was performed to investigate the effects of the cohesionless backfill friction angle ϕ1 and the wall geometric parameters including the offset distance, the total wall height, the batter angle δ, the number of tiers n, and wall height ratio of adjacent tiers on the dimensionless equivalent earth pressure coefficient KT. The analysis results demonstrated that as the ϕ1 increases, the shear strength of backfill is enhanced and thus the KT or the total reinforcement tensile force decreases, and the KT decreases with the increase of the offset distance at the initial stage and then becomes stable when it reaches a certain critical value. For a fixed offset distance, the KT or the total reinforcement tensile force decreases with the increase of the δ. For the two-tiered GRS walls having the offset distance less than the critical value, the wall with the smaller wall height ratio has a larger KT. Further, the variation of the location of the critical failure surfaces of tiered GRS walls was presented in this study with the variation of the ϕ1 and the wall geometry.

Utilizing PET bottles for sustainable cellular reinforcement: A study on enhancing fly ash backfill bearing strength with innovative geocell alternative

The slow degradation rate is one of the major global concerns. Only, 60 % produced is being recycled. Among these waste materials, Polyethylene Terephthalate (PET) bottles contribute around 10 % to the total plastic waste produced. The recycling process of PET bottles considering existing capacity in environmentally responsible ways is limited. It is estimated that 60 % of PET bottles produced are being disposed of in landfills. To overcome this, past studies have suggested novel approaches for using it as substitute for conventional geocell as soil reinforcement and stability. However, past studies mostly focused on application of PET bottles as flaked, shreds and sliced form. The present study attempts on application of PET bottles under fly ash (FA) backfills without mechanical alterations. Full-scale experiments were conducted on FA backfill system, for both unreinforced and reinforced conditions. A comparative study was performed between high-density polyethylene (HDPE) geocell and PET bottle mattress to assess the bearing strength of the FA backfill. Experiments were performed in a 1 m3 tank with a loading plate width of 200 mm. Vertical loading was applied onto the backfill footing (for all the trial series), till the footing settlement of 40 mm is achieved. An aspect ratio of 2 was considered for HDPE geocell and PET bottles. Rock quarry dust (RQD) was considered as cell infill and overlay material on FA backfill. The test results showed that settlement accumulation rate was low under reinforced scenario compared to the unreinforced condition, with higher resilient (elastic) settlement. RQD over the PET-reinforced zone was also seen to have enhanced the load distribution aspect, thereby reducing deformation in PET reinforcement. This usage of waste material will contribute towards sustainable development. This work demonstrates the feasibility and effectiveness of PET reinforcement to be used as replacement for HDPE geocell, which eventually can agument the design methodology of structural backfills.

Evolution law and mechanism analysis of strength for backfill under different stress and drainage conditions

In recent years, with the improvement of construction safety requirements in deep well mining, the backfill mining method has been widely used. However, the strength of paste filling acquired in quarry often surpasses the design strength determined in laboratory settings. In view of the problems that indoor conditions cannot restore deep mining environment, and the mechanism of coupling effect under multiple fields is unclear. This paper has carried out relevant research work through theoretical analysis and indoor experiments. First of all, after completing the preparatory experiments, this paper analyzed the strength difference of backfill under different curing stress and drainage conditions, and studies the influence of different curing conditions on the strength. Secondly, MPS-6 and 5TE sensors were used to monitor the electrical conductivity, pore water pressure, porosity and other parameters of backfill during the stress-drainage curing process, and changes of parameters during curing process were analyzed. Finally, the relationship among relevant parameters and strength properties of paste backfill was analyzed, as to clarify the influence mechanism of stress-drainage curing conditions on the strength formation for paste backfill. Research shows that both stress-undrained and stress-drained conditions can effectively increase the strength of backfill. Under stress-drainage conditions, the internal porosity of backfill will decrease, and the pore water pressure of backfill will first increase slightly and then continue to decrease. Under this condition, the electrical conductivity of backfill will first increase and then continue to decrease. The entire research has important positive significance for reducing mining costs, optimizing mining processes, and developing mining technology.

Enhancing the physical properties of cemented ultrafine tailings backfill (CUTB) with fiber and rice husk ash: Performance, mechanisms, and optimization

A series of experiments was conducted to study the performance and mechanisms of Cemented Ultrafine Tailings Backfill (CUTB). Firstly, the optimum fiber type was selected by single factor multilevel test. Secondly, the effects of cement content, rice husk ash content, fiber content and fiber length on backfill properties were analyzed by orthogonal test and microstructure test, and the influence mechanism of fiber and rice husk ash content was revealed. Finally, fuzzy mathematics theory is used to optimize the ratio parameters. The results show, compared to glass and basalt fiber, polypropylene fiber yields the most substantial enhancement in backfill strength. The increase of cement content, polypropylene fiber content and length can reduce slump, but the change of rice husk ash content has no obvious effect. Increased cement or fiber content effectively restrained the formation of primary fractures in CUTB, thus enhancing its integrity. Adding an optimal dosage range of 0–4 % of rice husk ash boosted the early compressive strength, albeiting at the expense of later compressive strength. Fiber addition with the optimum content range between 0.1 and 0.4 % enhanced the strengthening effect of cement content on compressive strength. Fiber primarily enhances the macroscopic strength of backfill through the dispersion and co-loading of forces, whereas rice husk ash enhances strength by optimizing void structure distribution. The optimal ratio parameters of a cement content of 310 kg/m³, rice husk ash content of 8.0 %, fiber content of 0.4 %, and fiber length of 9 mm were proposed finally.

Strength distribution of cemented waste rock backfill: a similarity simulation experiment

Backfill of cemented waste rock into underground mined-out areas is an effective way to eliminate solid wastes and potential hazards in mines. To understand the backfill strength distribution law throughout the stope, similarity simulation experiments were conducted for direct-irrigating cemented waste rock backfill, and OpenCV and neural network were employed to analyze particle segregation and the spatial distribution of backfill strength. Results show that distinct gravitational segregation leads to an uneven and heterogeneous distribution of natural graded waste rocks in a similar model. Backfill strength near sidewalls and bottom of the model surpasses that of other areas. In the vertical direction, the average backfill strength increases with depth, ranging from 1.15 MPa at the topmost layer to 1.91 MPa at the bottommost layer. Horizontally, the average backfill strength near model boundaries is consistently higher than that at the model center, irrespective of the layer depth and orientation. Neural network prediction on spatial backfill strength proves reliable, exhibiting an average relative error of 4.12%, compared to the traditional surface fitting with a 10.20% error. Verification tests affirm the capability of the neural network model to accurately predict the anisotropic and nonlinear distribution of backfill strength in a large stope.

Early mechanical strength, hydration mechanism and leaching behavior of alkali-activated slag/fly ash paste filling materials

The enhancement of the early strength of the filling body is regarded as a critical technology for shortening the mining & filling cycle and achieving efficient production. It is a high-value utilization pathway to entirely replace Ordinary Portland Cement (OPC) with industrial waste residue. Hence, in this research, ground granulated blast furnace slag (GGBFS) and fly ash (FA) were selected as aluminosilicate precursors. The effects of single-component and binary activation of Na2SiO3, Na2SO4, Na2CO3, NaOH, NaAlO2 and triethanolamine (TEA) on the mechanical strength of backfill were systematically investigated. The microstructural evolution mechanism of hydration products was elucidated using XRD, TG-DTG, SEM and MIP analyses. The leaching characteristics and immobilization mechanism of heavy metals were further revealed. The experimental results indicated that the activator contributed an alkaline environment and active ions to the initial hydrolysis reaction of precursors and the polycondensation reaction of silica tetrahedra and aluminum tetrahedra with Ca2+ drove the hardening and development of the hydration products. Na2SiO3 exhibited the superior activation effect among single-component activators, while the binary activator presented notable “promoting and inhibiting characteristics”. Moreover, the binary activator composed of 4% Na2SiO3 and 4% NaAlO2 conducted the highest compressive strength at 3 d and 7 d. The dominant hydration products of the backfill were ettringite, C-S-H gels, C-A-S-H gels and zeolite-like products. The density of microstructures and the crystallinity of hydration products were significantly enhanced ascribed to the synergistic and complementary effects of Na2SiO3 and NaAlO2. Heavy metals were immobilized by the hydration products through physical encapsulation and chemical bonding, and the leaching concentrations of all heavy metals (Pb, Cd, Cr(Ⅵ), Zn, Mn, As and Cu, etc.) were lower than the standard limits of Class III in GB/T 14848-2017.

Paraffin–CaCl2·6H2O dosage effects on the strength and heat transfer characteristics of cemented tailings backfill

Paraffin–CaCl2·6H2O dosage effects on the strength and heat transfer characteristics of cemented tailings backfill