Cemented Paste Backfill Research Articles

The mesostructure evolution of cemented paste backfill during mixing

Mixing plays a crucial role in preparing Cemented Paste Backfill (CPB). Shearing, concentration, and particle size distribution are key factors that impact the flow of CPB slurry. This study employed focused beam reflectance measurement and a torque sensor to monitor the flow and structure evolution of CPB during the mixing process. The mixing process can be divided into three stages based on the torque curve: aggregation, destruction, and equilibrium. The structural evolution is the cause of the flow of fresh CPB. Each stage exhibits distinctive characteristics of the fresh CPB. During the aggregation stage, coarse tailings agglomerate via liquid bridges, binders agglomerate by hydration, and fine tailings interact mostly due to interparticle forces. Since the network is heterogeneous, the structure cannot resist shearing forces during the destruction and equilibrium stages. Finally, a rheological model was developed based on the mesostructure evolution mechanism of CPB.

Impact of virgin and recycled polymer fibers on the rheological properties of cemented paste backfill

The addition of polymer fibers to cemented paste backfill (CPB) has shown promise in enhancing mechanical properties, although it also introduces changes in rheological characteristics. This study aimed to investigate the influence of different types of polymer fibers, namely virgin commercial polypropylene fiber (CPPF), recycled tire polymer fiber (RTPF), and recycled tire rubber fiber (RF), on the rheological properties of CPB mixtures through an experimental program, and provide design references for CPB pipeline transport. The results revealed consistent reductions in bulk density upon the incorporation of polymer fibers into CPB, alongside varying impacts on slump. Specifically, the addition of CPPF had a mild effect, while RTPF caused a continuous decrease in slump, and RF exhibited minimal influence up to a 4% concentration, with substantial effects thereafter. Moreover, the inclusion of fibers led to increases in apparent viscosity parameters, with RTPF inducing the most significant changes, followed by varying responses from CPPF and RF. When using RTPF for CPB reinforcement, emphasis should be placed on enhancing technical indicators related to viscosity such as energy consumption and pipeline wear during pipeline transport. Furthermore, adjustments were necessary to account for flow curve instability resulting from interactions between fibers and the paddle, with the data aligning well with the Bingham model. The addition of fibers, particularly CPPF and RF, primarily influenced plastic viscosity rather than yield stress, underscoring the limitations of slump tests in assessing rheology.

Deformation field evolution characteristics of layered cemented paste backfill and strength prediction based on ultrasonic pulse velocity

ABSTRACT This study focused on investigating the damage development mode and strength prediction model of layered cemented paste backfill (LCPB) using digital image correlation (DIC) and ultrasonic pulse velocity (UPV). The results indicated that the damage mode was associated with the cement-to-tailings (c/t) ratio and the height (h/H) ratio of the middle layer of LCPB. The damage mode of LCPB was mainly tensile damage for a small h/H ratio while increasing the h/H ratio to 0.8 resulted in LCPB exhibiting macroscopic shear damage. With the reduction of the c/t ratio, the damage area of LCPB gradually shifted from the upper layer to the middle layer. The UPV tended to decrease exponentially with both the decrease of the c/t ratio and the increase of the h/H ratio. Comparing the predicted and experimental values, the maximum error of the predicted values was only 0.299, and the value of the a20-index was 0.9792, indicating that the predictive model was reliable. The findings could provide guidance for the design of LCPB.

Experimental Investigation of Recycling Cement Kiln Dust (CKD) as a Co-Binder Material in Cemented Paste Backfill (CPB) Made with Copper Tailings

Experimental Investigation of Recycling Cement Kiln Dust (CKD) as a Co-Binder Material in Cemented Paste Backfill (CPB) Made with Copper Tailings

Study on microstructure of cemented paste backfill with initial defects under uniaxial compression failure

In order to fully understand the micro and fine structural characteristics of the cemented paste backfill (CPB) with initial defects, this paper carries out uniaxial compression test on the CPB and real-time monitoring with DIC technology, analyses the crack extension and deformation characteristics on the surface of the specimen, carries out SEM test on the damaged specimen, binarizes the SEM images, and performs microscopic pore analysis on the processed binarized images using PCAS software. Then some parameters such as porosity, probability entropy, probability distribution index, fractal dimension, form factor, etc. of the specimens with different initial defects are discussed. The study shows that the damage form of CPB under uniaxial compression is mainly tensile damage, and gradually changes from tensile damage to shear damage when the specimen reaches the peak strength. The overall displacement and strain of each monitoring point on the specimen increases rapidly after entering the plastic deformation stage. There are many small microcracks and pores in the CPB, and there are a large number of aciculate ettringite and C-S-H gel hydration products, which are generated in the sample unevenly. With the addition of air-entraining agent (AEA), within a certain range, the number of pores inside the CPB increases. Many small pores also form large pores because of the connectivity between the pores, the porosity of the specimen increases, and the morphology and structure of the pores are relatively more regular. However, the direction of the pore development still does not have good directionality, and the initial defects become increasingly obvious.

Strength Development of Cemented Paste Backfill with CaCl2 and NaCl in Above-Zero Underground Environments

Strength Development of Cemented Paste Backfill with CaCl2 and NaCl in Above-Zero Underground Environments

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.

Energy and deformation field evolution characteristics of layered cemented paste backfill under cyclic loading and unloading

Due to the mining environment, layered cemented paste backfill (LCPB) is usually subjected to the cyclic pressure. Therefore, it is of great significance to investigate the mechanical behavior, failure mode and energy evolution characteristics. LCPB samples were prepared and subjected to constant lower limit cyclic loading and unloading test. The digital image correlation (DIC) technology was applied to monitor deformation field of LCPB. The obtained results indicate that: (1) The area of the hysteresis loops increases sequentially with increasing unloading stress level, while the spacing between the hysteresis loops gradually increases, showing the typical “dense-sparse” two-stage variation law. (2) Energy density and the unloading stress level is in agreement with the power function. The limiting elastic energy density (uemax) shows a linear decrease with the increase of h. The exponential function can well characterize the quantitative relationship between uemax and c/t ratio. (3) The damage mode of LCPB gradually tends to x-shape shear-dominated damage with the increase of h. The damage mode of LCPB is gradually dominated by shear-type damage with the decrease of c/t ratio. Ultimately, the findings of this work can provide a reference for the design of LCPB.

Study On Mechanical Properties Of Cemented Paste Backfill Using Fly-Ash-Based Cementitious Materials

In Mongolia, the Ulan lead-zinc mine is now struggling with high backfill operating costs and poor Cemented Paste Backfill (CPB) mechanical performance after curing. To solve this problem, BGRIMM Technology Group has investigated an activator that could mix with fly ash from Choibalsan Power Plant in Mongolia as a supplementary cementitious material for backfill. In this study, the mechanical performance of CPB samples prepared with various fly ash content and activator types were studied to provide a basis for the industrial application of fly ash-based supplementary cementitious materials. The research results indicate that partially replacing cement with fly ash reduces the uniaxial compressive strength (UCS) of CPB samples. Compared with the CPB sample prepared with pure cement, when the fly ash substitution rate is 10%, 20%, and 30%, the UCS reduced by 15.66%, 18.69%, and 32.83%, respectively. With the use of chemical activators, the UCS of CPB samples could be significantly improved. Among them, CPB samples prepared by the activator sodium sulfate+ sodium chloride+ TEA have achieved the highest UCS. Overall, this study shows that the synergistic effect of fly ash and chemical activators could effectively enhance the mechanical performance of CPB, which is beneficial for mine backfill cost reduction and could provide a basis for the further industrial application of fly ash-based cementitious materials in mine backfill.

Experiment and numerical simulation study of polycarboxylate superplasticizer modified cemented ultrafine tailings filling slurry: Rheology, fluidity, and flow properties in pipeline

Understanding the rheological properties of cemented paste backfill is crucial for optimizing its flowability and ensuring the efficient transportation in mine site. Due to the superfine size, the high-concentration filling slurry prepared by ultrafine tailings (the mean size < 0.019 mm) usually exhibits poor flow performance. In this study, the polycarboxylate superplasticizer (PCS) was adopted as an additive to modify cemented ultrafine tailings filling slurry. Experiment tests and numerical simulation were conducted to investigate effects of PCS dosages, solid and binder contents on rheological, fluidity, and flow performance. Results indicate that the PCS modified filling slurry conforms to Bingham model and shows shear-thinning behavior. As PCS dosage increases from 0 to 0.30 wt%, the yield stress gradually decreases, whereas the plastic viscosity initially increases then decreases. The electrostatic repulsion and steric hindrance generated by PCS can disintegrate the floc structures formed by ultrafine particles, leading to more release of free water, and reducing interparticle friction, correspondingly, improving flowability of filling slurry. The optimal PCS dosage is determined as 0.15–0.25 wt% considering transportation requirement. For a given PCS dosage, the yield stress and plastic viscosity exhibit an exponential growth with solid content, while a continuous decline with binder content. Furthermore, the fluidity increases linearly and exponentially with PCS dosage for filling slurry at solid content of 59–62 wt% and 63 wt%, respectively. An exponential model is established to quantify the relationship between yield stress and fluidity, which provides a method for predicting rheological parameters. With addition of PCS dosage, the flow performance of filling slurry is enhanced significantly in transportation pipeline. The maximal flow velocities at the pipeline center increase, and those near the pipeline wall decrease. The findings afford a practical guidance for designing and optimizing materials proportions of PCS modified filling slurry to achieve the desired flowability in mine site.

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.

A state-of-the-art review on delayed expansion of cemented paste backfill materials

A state-of-the-art review on delayed expansion of cemented paste backfill materials

Using cemented paste backfill to tackle the phosphogypsum stockpile in China: A down-to-earth technology with new vitalities in pollutant retention and CO2 abatement

Using cemented paste backfill to tackle the phosphogypsum stockpile in China: A down-to-earth technology with new vitalities in pollutant retention and CO2 abatement

Dynamic Loading Characteristics of Cemented Paste Backfill with Recycled Rubber

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.

Calcined alunite-modified alkali-sulphate-activated slag as a novel binder for high-performance cemented paste backfill

The free water content and pore structure significantly affect the mechanical properties of cementitious materials. Because of high water-to-cement ratio and low binder dosage, cemented paste backfill (CPB) is characterized by high free water content and high porosity, which lead to a low strength. In this study, calcine alunite (CA) was used to modify the alkali-sulphate-activated slag (ASAS) to synthesis high-strength CPB with low porosity and low free water content. The results show that at dosage ≤3 %, CA can significantly enhance the strength of ASAS-CPB, and the strengthening effect becomes more prominent as both the dosage and curing time rise. An addition of 3 % CA leads to a 184 % increase in strength at 14 days. However, excessive CA (5 %) reduces 3-day strength by 65 %, but provides the greatest strength at 56 days. As the dosage increases up to 3 %, the promoting impact of CA on early hydration of ASAS-CPB gradually increases, and the duration of induction stage and acceleration stage gradually decreases. Nevertheless, 5 % CA prolongs the duration of induction stage by 921 %. Electrical conductivity and volume water content can be used to assessing the hydration process of ASAS-CPB. Besides, the addition of CA can promote the hydration of slag, resulting a greater formation of C–S–H and ettringite. The hydration products fill the pores and transform the macropores into micropores. Furthermore, mechanisms of CA-induced enhancement in strength is discussed. The results of this study can offer a reference for the synthesis of high performance CPB.

The Impact of Temperature on the Triaxial Compression Characteristics of Cemented Paste Backfill

In deep well mining, due to the influence of the surrounding environmental temperature, the mechanical properties of the cemented paste backfill (CPB) will change. Therefore, studying the effect of temperature on the mechanical characteristics of CPB is of great research significance for the safety and stability of the mining stope. This article conducted triaxial compression tests on CPB at different temperatures, studied the effect of temperature on the shear strength characteristics of CPB specimens, and investigated the failure mechanisms and characteristics of CPB. The results show that: (1) The cohesion and internal friction angle of CPB specimens increase with increasing temperature. (2) As the temperature increases, the failure mode of CPB specimens changes from single oblique section shear failure to Y-type failure.

An Experimental Study on the Mechanical Properties and Microstructure of the Cemented Paste Backfill Made by Coal-Based Solid Wastes and Nanocomposite Fibers under Dry-Wet Cycling.

The mechanical properties and microstructure of the cemented paste backfill (CPB) in dry-wet cycle environments are particularly critical in backfill mining. In this study, coal gangue, fly ash, cement, glass fiber, and nano-SiO2 were used to prepare CPB, and dry-wet cycle tests on CPB specimens with different curing ages were conducted. The compressive, tensile, and shear strength of CPB specimens with different curing ages under different dry-wet cycles were analyzed, and the microstructural damage of the specimens was observed by scanning electron microscopy (SEM). The results show that compared with the specimens without dry-wet cycles, the uniaxial compressive strength, tensile strength, and shear strength of the specimens with a curing age of 7 d after seven dry-wet cycles were the smallest, being reduced by 40.22%, 58.25%, and 66.8%, respectively. After seven dry-wet cycles, the compressive, tensile, and shear strength of the specimens with the curing age of 28 d decreased slightly. The SEM results show that with the increasing number of dry-wet cycles, the internal structure of the specimen becomes more and more loose and fragile, and the damage degree of the structural skeleton gradually increases, leading to the poor mechanical properties of CPB specimens. The number of cracks and pores on the specimen surface is relatively limited after a curing age of 28 d, while the occurrence of internal structural damage within the specimen remains insignificant. Therefore, the dry-wet cycle has an important influence on the both mechanical properties and microstructure of CPB. This study provides a reference for the treatment of coal-based solid waste and facilitates the understanding of the mechanical properties of backfill materials under dry-wet cycling conditions.

Research on Slurry Flowability and Mechanical Properties of Cemented Paste Backfill: Effects of Cement-to-Tailings Mass Ratio and Mass Concentration.

The flowability and mechanical properties are increasingly crucial in the filling process of deep metal mines with mining depths exceeding 1000 m. The rheological properties of filling slurry in the pipeline were analyzed through rheological tests, L-tube self-flow tests, and semi-industrial loop tests. The results revealed that with an increase in the cement-to-tailings mass ratio (c/t ratio) and mass concentration, the slurry exhibited a higher flow resistance and decreased stowing gradient. During slurry transportation, the pressure loss in the straight pipe was positively correlated with the slurry flow rate, c/t ratio, and mass concentration. A uniaxial compressive strength (UCS) test was conducted to analyze the mechanical properties of the cemented paste backfill containing BMC (CCPB) in both standard and deep-underground curing environments. The UCS of the CCPB showed an increasing trend with the rise in curing age, mass concentration, and the c/t ratio. The comprehensive analysis concluded that when the c/t ratio is 1:4, and the mass concentration is approximately 74%, and parameters such as the slump, bleeding rate, and flowability of the filling slurry meet the criteria for conveying and goaf filling, resulting in a high-strength filling body.

Developing interpretable machine learning model for evaluating young modulus of cemented paste backfill

Cemented paste backfill (CPB), a mixture of wet tailings, binding agent, and water, proves cost-effective and environmentally beneficial. Determining the Young modulus during CPB mix design is crucial. Utilizing machine learning (ML) tools for Young modulus evaluation and prediction streamlines the CPB mix design process. This study employed six ML models, including three shallow models Extreme Gradient Boosting (XGB), Gradient Boosting (GB), Random Forest (RF) and three hybrids Extreme Gradient Boosting-Particle Swarm Optimization (XGB-PSO), Gradient Boosting-Particle Swarm Optimization (GB-PSO), Random Forest-Particle Swarm Optimization (RF-PSO). The XGB-PSO hybrid model exhibited superior performance (coefficient of determination R2 = 0.906, root mean square error RMSE = 19.535 MPa, mean absolute error MAE = 13.741 MPa) on the testing dataset. Shapley Additive Explanation (SHAP) values and Partial Dependence Plots (PDP) provided insights into component influences. Cement/Tailings ratio emerged as the most crucial factor for enhancing Young modulus in CPB. Global interpretation using SHAP values identified six essential input variables: Cement/Tailings, Curing age, Cc, solid content, Fe2O3 content, and SiO2 content.