Cemented Paste Backfill Samples Research Articles

Durability and heavy metals leaching behavior of cemented paste backfill using chemical activated binary slag as binder under sulfate attack

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.

Testing the properties of cemented tailings backfill under multiaxial compressive loading

The engineering design of cemented paste backfill (CPB) typically relies on technical data obtained from tests conducted on CPB samples cured under conventional laboratory conditions. However, these methods often fall short in capturing the complex multiaxial stress curing conditions that CPB masses experience in many underground mines, particularly in deep underground mines. In these mining environments, CPB is subjected to multi-axial stress conditions during the curing process that are challenging to replicate in a controlled laboratory setting. No lab-scale apparatus can currently accurately reproduce these actual field multiaxial stress conditions, especially the intricate interplay of horizontal rockwall closure stresses, vertical self-weight stress, and overburden stresses from upper layers. Moreover, the impact of these conditions on the key engineering properties of CPB is unknown. To address this significant challenge and technology gap, this study has developed a new apparatus for curing and monitoring CPB under realistic multiaxial compressive loading conditions, simulating the complex stress environment encountered in underground mines. The developed apparatus was then utilized to assess the impact of multiaxial stress curing conditions, including vertical stress and horizontal stresses induced by rockwall closures, on key engineering properties (strength, deformation behaviour, self-desiccation) of CPB at early ages. The research results clearly indicate that the application of multiaxial stresses leads to a significant enhancement in the mechanical and physical properties of CPB. This enhancement is supported by observable densification of the pore structure in CPB subjected to multiaxial compressive stresses. In addition, a comprehensive analysis of deformation and strain patterns establishes a direct correlation between multiaxial stresses and the progressive increase in stiffness and hardness of CPB over time. Furthermore, the evolution of matric suction and degree of saturation provides compelling evidence of the significant impact of multiaxial stresses on pore water consumption or self-desiccation. The development of this new apparatus fills a substantial void in CPB research capabilities. Furthermore, the results obtained provide a better understanding of the complex behavior of CPB in multi-stress loading environments, paving the way for the design and optimization of backfill solutions that effectively address the unique challenges posed by deep underground mining operations.

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.

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 curing humidity on the deformation and mechanical properties of cemented paste backfill

ABSTRACT 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.

The effects of arsenic trioxide addition on the mechanical and geochemical properties of the cemented paste backfill

Cemented paste backfill (CPB) technology, a densified mixture of mine tailings, binding material, and water, thickens to form a non-settling paste that is transported to fill mined cavities. CPB could provide environmental advantages by preventing the release of contaminants through hydraulic binder stabilization/solidification. Up to now, only few studies have been carried out to examine the feasibility of arsenic (As) fixation within cemented paste backfills. The main objective of the current study is to assess the impacts of incorporating pure arsenic trioxide on the geomechanical and geochemical properties of cemented paste backfill. CPB samples were prepared using pure ground silica (Sil-Co-Sil®) mimicking mine tailings, general use (GU) cement, deionized water, and reagent-grade pure As2O3 at different arsenic contents (0, 5, 10, and 15%). The samples were cured for up to 28 days and unconfined compressive strength (UCS) tests were conducted after 7 and 28 days of curing. Moreover, to evaluate the geochemical behavior of the pastes, mixtures of GU cement, pure As2O3 (0–15%), and deionized water with the same proportions as the CPB samples were prepared and mixed for up to 28 days. Then, pH, EC and chemical composition of the mixtures were evaluated. Results showed that the addition of pure arsenic trioxide (as a partial substitution for pure silica) leads to a substantial decrease in the mechanical strength of the CPB samples. However, this adverse effect was more substantial for the arsenic content of 5 wt%. The strength of the As2O3-containing samples did not improve significantly after 7 days of curing and arsenic addition lowered the pH of the solutions Microstructural analysis using SEM proved the formation of some C–S–H gels that contained arsenic in their structures as well as some complex mixture of oxides for the case of the As2O3-cement mixtures.

Strength, Deformation Behavior, and Microstructure of Cement Paste Backfill with Calcium Chloride in Subzero Environments

This manuscript presents and discusses the results of an experimental study on the deformation behavior, strength, and microstructural development of cemented paste backfill (CPB) with chloride-bearing antifreeze (calcium chloride, CaCl2) in subzero environments. CPB samples with CaCl2 at various concentrations (0, 5, 15, and 35 g/L) were cured at different subzero temperatures (−1, −6, and −12°C) that represent temperatures to which CPBs may be exposed in mines located in permafrost or cold regions. Unconfined compressive strength (UCS) tests were conducted after specific curing time (7, 28, 60, and 90 days). Moreover, microstructural analyses and monitoring experiments (for volumetric water content and matric suction) were performed. The results showed that the addition of calcium chloride antifreeze reduced the strength of CPB and had a significant impact on its stress–strain behavior and microstructural characteristics. Furthermore, it was also found that the strength of CPB decreased with an increase of calcium chloride concentration and subzero curing temperature. These findings provide important guidance for mine backfilling work of CPB with chloride-bearing antifreeze additives and productivity improvement in subzero environments.

Application of deep neural network in the strength prediction of cemented paste backfill based on a global dataset

With the development of the mining industry, the increasing global content of tailings is causing environmental pollution and the use of tailings as a cemented paste backfill (CPB) for underground filling is an effective method of disposal. The application of the backfilling mining method is heavily dependent on the stability of the CPB. However, experimentally evaluating the unconfined compressive strength (UCS) of CPB is time-consuming and expensive. This study discussed the feasibility of using a deep neural network (DNN) model to predict the UCS of CPB. This study established the first global dataset of UCS values of CPB through a literature search and laboratory studies, for the first time. The dataset comprised 986 CPB samples, where each sample included 14 feature values and a target value. The dataset was divided into three parts, i.e., a training set, a validation set, and a testing set, which were used to build, validate, and test the model. The correlation coefficient (R), coefficient of determination, mean absolute error, and mean square error metrics were used for model evaluation. After the hyper-parameter tuning, the number of layers in the DNN model was 4, the learning rate was 0.001, and the dropout rate was 0.25. The optimal DNN model achieved excellent predictive performance on this dataset, with R values on the training, validation, and testing sets of 0.989, 0.964, and 0.967, respectively. The feature importance was analyzed using permutation importance and the Shapley Additive Explanation value, with the cement–tailings ratio found to be the most important feature value with the greatest impact on the model output. This study provides, for the first time, a UCS prediction based on the global CPB dataset, a method that can quickly and accurately obtain the UCS of CPB. The method can save a lot of experimental time and provide a theoretical reference for subsequent environmental management as well as tailings utilization, and promotion of paste filling.

Preparing new supplementary cementitious materials with co-calcined waste glass-dolomite and environmental assessment

Recycling waste glass (WG) for supplementary cementitious materials is one of the most viable methods to address the environmental issues of waste generation. In this study, homogenised WG–dolomite with different mass ratios was first calcined at 800 °C and 1000 °C. Then non-cement clinker cementitious materials (NCCMs) were prepared by mixing calcined WG–dolomite, superfine slag (SS) and flue gas desulphurisation gypsum. Finally, coupled with silica tailings, NCCMs were used to prepare cemented paste backfill (CPB) samples. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), Isothermal calorimeter, Thermogravimetry (TG) and scanning electron microscopy (SEM) were employed to study the thermal transformation of calcined WG–dolomite and microstruction evolution of NCCMs hydration. The experimental results show that the main products of calcined WG–dolomite have high contents of MgO, calcite and CaO at 800 °C, whereas they have large proportions of C2S and CA at 1,000 °C. As the calcination temperature increases, the chemical shift of 29Si moves steadily towards higher frequencies, indicating the dominance of Q0/Q1 sites from silicate. In addition, the high contents of MgO and CaO in calcined WG–dolomite accelerate NCCM paste hydration, which is conducive to the formation of C–A–S–H and M−S−H. Moreover, due to SS hydration being more dependent on alkaline environments, co-calcined WG-dolomite at 800 °C enables the CPB sample to have better mechanical performance.

Eco-Sustainable Recycling of Cement Kiln Dust (CKD) and Copper Tailings (CT) in the Cemented Paste Backfill

Cement global demand shows continued growth and a significant increase in the production volume, which may negatively impact the non-renewable natural resources and the environment, which is incompatible with sustainability goals. Cement kiln dust (CKD) is a primary concern associated with clinker manufacturing as a waste byproduct. Similarly, the mining industry produces copper tailing as unwanted material while beneficiating the ore, creating environmental problems due to difficulty in managing worldwide generated quantities that reach billions of metric tons. This study investigated the beneficial utilization of cement kiln dust and copper tailing as undesirable wastes in industrial applications through underground mines’ cemented paste backfill (CPB). Sixty different mixtures were prepared with three types of CKD collected from various cement manufacturers and were accordingly used with a proportion of 5, 10, and 15% to partially replace ordinary Portland cement (OPC) and pozzolan Portland cement (PPC) binders, represented in hundreds of CPB samples. The hardened specimens were subjected to density, uniaxial compressive strength (UCS), and axial deformation measurements to evaluate the physical and mechanical properties at curing up to 90 days. Meanwhile, X-ray powder diffraction (XRD) was extensively applied to chemically investigate the hydration products of CPB-hardened mixtures. Moreover, we developed a UCS predictive model applying two techniques: multiple variables regression analysis and artificial neural network (ANN). The results showed that the tricalcium silicate (Alite) and dicalcium silicate (Belite) phases form C-S-H upon hydrations and provide high strength in the binary mixtures. Meanwhile, the CKD’s lime saturation factor (LSF) governed the strength value in the ternary mixtures that utilized copper tailings. That makes CKD practical in the CPB mixture when partially replacing the OPC and PPC binders, with a proportion of up to 15%. In addition, the ANN technique’s predictive model exhibited a significant positive correlation with excellent statistical parameters that achieved 0.995, 0.065, and 0.911 for R2, RMSE, and MAE, respectively.

Modification of cemented paste backfill with calcined layered double hydroxides for lead-containing tailings disposal

Cemented paste backfill (CPB) is the main way to treat tailings at present. Alternative binders are necessary due to the high cost and CO 2 emission of ordinary Portland cement . Besides, the heavy metals contained in the tailings should be immobilized effectively when being used in CPB. In the present work, calcined Mg-Al-layered double hydroxides (CMA) were used to modify the properties of high-volume fly ash (FA) cement to increase its performance in CPB. Isothermal calorimetric, X-ray diffraction, and thermogravimetric analysis were used to explore the reaction kinetics and phase assembles of the binder. The properties of CPB samples were then studied. In addition, the lead (Pb) immobilization effects in CPB samples were studied using toxicity characteristic leaching procedure and semi-dynamic leaching. The experimental results proved that CMA could accelerate binder reaction by providing additional nucleation sites for hydration gel formation. It then increased the compressive strength of CPB samples. Besides, the immobilization effects of Pb were enhanced when adding CMA due to the better immobilization capacity of regenerated LDHs. • CMA provided more nucleation sites for hydration gels formation. • CMA could increase the yield stress of fresh CPB slurry. • The presence of CMA increased Pb immobilization effects of CPB. • The leaching of Pb from CPB was controlled by diffusion.

Novel SCMs produced by the calcination of secondary aluminium dross with dolomite and their potential usage in cemented paste backfill

In this study, novel supplementary cementitious materials (SCMs) were produced by the mixed calcination of secondary aluminium dross and dolomite. The thermal activation effect on calcined mixes, hydration properties of pastes with the novel SCMs and workability of cemented paste backfill (CPB) were experimentally investigated. The results demonstrated that high-temperature calcination evidently increased the activity of SCM, and the improvement by thermal activation was positively correlated with calcination temperature. Pastes with calcined SCMs hydrated to form more CsbndSsbndH, ettringite and Ht but less portlandite because of the accelerated pozzolanic reaction of SCMs. Moreover, CPB samples with novel SCM had an imporved transportation performance and mechanical strength with denser pore structure. Furthermore, heavy metals (Cu, Pb, Zn and Cr) were well-immobilised/stabilised by CPB with novel SCMs calcined at 900 °C and 1,000 °C, which can make secondary aluminium dross be used without environmental risks.

Performance investigation of blast furnace slag based cemented paste backfill under low temperature and low atmospheric pressure

To promote application of cemented backfill mining in underground mines located at high-altitude regions, there is a necessary to investigate mechanical performance of cemented paste backfill (CPB) under low temperature and low atmospheric pressure. In this study, the orthogonal experiment was first scheduled to synthesize the new cementitious material by combining industrial byproducts of blast furnace slag (BFS), carbide slag (CS), desulfurization gypsum (DG) with cement clinker (CC). Then, CPB samples were prepared with the new cementitious material and cured under different temperatures of 5, 10, 20 ℃ and atmospheric pressures of 50, 75, 101 kPa for 3, 7 14, and 28 days. Unconfined compressive strength (UCS) and microstructural analyses were conducted to evaluate strength and microstructure evolution of CPB. Experimental results indicate that UCS values of CPB increase with BFS, but decrease with CS and DG. The optimal proportion of the new cementitious material is determined as: 70 wt% BFS, 12 wt% CS, 1 wt% DG, and 17 wt% CC. Under curing of low temperature and low atmospheric pressure, CPB samples exhibit lower UCS values than those under 20 ℃ with 101 kPa. Especially, the coupling of low temperature and low atmospheric pressure exerts significantly adverse influence on the later strength of CPB after curing of 14 and 28 days. The declines of 57.99 % and 41.75 % are observed from UCS values of 14-day and 28-day CPB under 5 ℃ with 50 kPa, respectively. Regardless of curing temperature and atmospheric pressure, UCS values increase with the ratio of cementitious material to tailings and curing time. Low curing temperature and low atmospheric pressure reduce the hydration degree of the new cementitious material. The amount of hydration products decreases, the number of micropores (0.1 ∼ 1 μm) and the total porosity increases, as well as more loose microstructure forms among solid particles. This is the underlying reason behind performance degeneration of CPB under low temperature and low atmospheric pressure.

Recycling of arsenic-containing biohydrometallurgy waste to produce a binder for cemented paste backfill: Co-treatment with oil shale residue.

The high cost of ordinary Portland cement (OPC) limits the broad usage of cemented paste backfill (CPB). Additionally, improper disposal of arsenic-containing biohydrometallurgy waste (BW) can cause tremendous pollution to the environment. Consequently, BW is used to prepare an alternative cementitious material for CPB in this study. The effect of calcined oil shale residue (COSR) on the binder's characteristics was studied. The reaction kinetics of the binder in the presence of COSR were studied via the isothermal calorimeter test and the Krstulovic-Dabic model; mechanical strength and hydration product modifications due to the addition of COSR were also investigated. The leaching of hazardous elements from the binder was also investigated. The results showed that adding COSR reduced the flowability of fresh slurry and early-age compressive strength; however, adding 20wt% COSR resulted in the highest later age compressive strength, thereby reaching ∼43.65MPa after 60 days. The compressive strength of the CPB sample using the COSR20 as a binder may reach ∼87% of the OPC-based CPB sample. Furthermore, the presence of COSR had no significant effect on the phase assembles but changed the amount of ettringite (AFt) and calcium silicate aluminate hydrate (C-A-S-H). The results of this study show that the prepared binder could be used as an alternative to OPC in CPB.

Effects of chlorides on setting time, hydration heat and hydration products of fresh slurry of cemented paste backfill

Mine water is rich in various chlorides, which will inevitably affect the performance of the cemented paste backfill (CPB). In this study, the TAM Air isothermal calorimeter was used, the effects of typical chlorides (NaCl, CaCl2 and MgCl2) in mine water on the hydration heat and hydration heat flow in the solidification stage of fresh CPB were studied, and the effects of chlorides on the setting time of fresh CPB were analyzed. The hydration products of CPB samples containing different chlorides were tested by the X-ray diffractometer and thermal gravimetric analyzer. The results show that NaCl and CaCl2 can promote the early hydration reaction of CPB; and the promoting effect of CaCl2 is more significant; while MgCl2 consumes OH- in the solution and reduce the pH of the solution, thus inhibiting the early hydration reaction of CPB. With the increase of chloride concentration, the promoting effect of NaCl on the early hydration of the CPB first increases and then decreases, the promoting effect of CaCl2 increases constantly, and the inhibitory effect of MgCl2 also increases continuously. Besides, CaCl2 can significantly shorten the hydration time of CPB in the induction stage and acceleration stage, and the higher the CaCl2 concentration, the higher the cumulative hydration heat and the hydration heat release rate of CPB in the same hydration stage. This study comprehensively evaluates the influence of typical chlorides in mine water on the early hydration process and setting time of the fresh CPB, providing a reference for the clean utilization of mine water, fly ash, gangue and other solid wastes.

Effect of Waste Materials on the Strength-Stability Performance and Production Cost of Cemented Paste Backfill

Bu çalışma ile çimentolu macun dolgu (ÇMD) karışımında sülfürlü-maden atığı (S-MA) yerine %15 oranında ikame edilen atık malzemelerin (inşaat-yıkıntı atığı: İYA, kireçtaşı: KT, uçucu kül: UK ve yüksek fırın cürufu: YFC) ÇMD’nin dayanım/duraylılık performansına ve üretim maliyetine etkisi incelenmiştir. Bu amaçla, üretilen ÇMD numuneleri (kontrol: ve %15 atık malzeme ikameli) 7-360 gün boyunca dayanım testine tabi tutulmuştur. ÇMD üretim maliyetinin araştırılması için karışımlarda kullanılan çimento miktarları ve maliyetleri belirlenirken, atık malzemelerin öğütme sırasındaki enerji tüketimleri ve maliyetleri hesaplanmıştır. Tüm numuneler kısa ve uzun dönemde istenen 1,0 MPa dayanımı sağlamış ve %15 UK ve YFC ikameli ÇMD numuneleri kontrol numunelerine kıyasla 4 kata kadar daha yüksek dayanım üretmiştir. 1,0 m3 ÇMD üretimi için kontrol karışımında 130,0 kg çimento (%8,5) kullanılırken, atık malzeme ikameli karışımlarda bağlayıcı oranının %1,0 düşürülmesi yaklaşık %15 çimento tasarrufu sağlamıştır. Atık malzemelerin öğütme işlemlerinde 6,55-18,89 kW-saat/ton elektrik enerjisi tüketilmiş ve böylece 2,99 ₺ (UK)-8,85 ₺ (İYA) arasında para harcanmıştır. ÇMD üretimi için toplam maliyet değerlendirildiğinde, kontrol karışımı için 153,4 ₺ harcanırken, %15 atık malzeme ikameli karışımların maliyetinin 133,5 ₺’ye kadar (%12,98’e kadar tasarruf) düşürülebilmesi öngörülmüştür. Sonuçlar, ÇMD’nin dayanım/duraylılık performansı ve üretim maliyeti konusunda en uygun karışım tipinin %15 UK ikameli ÇMD karışımı olduğunu göstermiştir.

Preparation and characterization of a new alkali-activated binder for superfine-tailings mine backfill.

Recently, the increasing of ultrafine-tailings increases the amount of ordinary Portland cement (OPC) in cemented paste backfill (CPB), which leads to the rise of CPB cost and carbon emission. As a result, it is necessary to develop alternative binders. The present work focuses on the preparation of a new binder, which is activated by a mixture of calcined quarry dust (CQD) and NaOH at a mass ratio of 1:1. The results indicated that CQD/NaOH was more effective than using NaOH or CQD alone in activating blast furnace slag (BFS) and also showed better performance than OPC. The compressive strength of the CPB samples using 10% CQD/NaOH was around 3.78MPa after curing for 90days, around 42% higher than the OPC-based CPB samples. The reaction products of CQD/NaOH-activated BFS consisted mainly of C-(A)-S-H, hydrotalcite like phases (Ht), and M-S-H. The generation of Ht phases lowered the Al incorporation into the structure of C-S-H, resulting in lower average Al/Si ratio and mean chain length.

Dual waste utilization in cemented paste backfill using steel slag and mine tailings and the heavy metals immobilization effects

Cemented paste backfill (CPB) is one of the effective means to disposal of mine tailings. During CPB process, ordinary Portland cement (OPC) is the most commonly used cementitious materials. The high price of OPC increases CPB cost. In the present work, a new binder was prepared using illite-containing mine tailings (IT) and steel slag (SS) after thermal treatment as supplementary cementitious materials (SCMs), which were then used in CPB. OPC was replaced by 30 wt%. The phase assembles of binders hydration products with different calcined IT (CIT), and SS (CSS) ratios were investigated via X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscopy (SEM) analysis. After that, properties of CPB samples were then characterized, including the flowability, setting time, compressive strength, and pore structure. The results showed that sample CIT10-CSS20 showed superior performance, which was comparable to OPC-based samples. Furthermore, the cost of binders was calculated using a mass-based analysis, and the results show that sample CIT10-CSS20 was cheaper than OPC. Heavy metals leaching concentration from this sample fulfilled the regulation limit.

Preparation and Strength Formation Mechanism of Calcined Oyster Shell, Red Mud, Slag, and Iron Tailing Composite Cemented Paste Backfill.

The use of bulk solid-waste iron tailing (IOT), red mud (RM), and oyster shells to prepare cemented paste backfill (CPB) can effectively solve the ecological problems caused by industrial solid waste storage and improve the utilization rate of such materials. In this study, a new type of CPB was prepared by partially replacing slag with RM, with calcined oyster shell (COS) as the alkaline activator and IOT as aggregate. The central composite design (CCD) method was used to design experiments to predict the effects of the COS dosage, RM substitution rate, solid mass, and aggregate–binder ratio using 28-dUCS, slump, and the cost of CPB. In this way, a regression model was established. The quantum genetic algorithm (QGA) was used to optimize the regression model, and X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS) microscopic tests are performed on CPB samples of different ages with the optimal mix ratio. The results showed that COS is a highly active alkaline substance that provides an alkaline environment for polymerization reactions. In the alkaline medium, the hematite and goethite in RM and quartz in IOT gradually dissolved and participated in the process of polymerization. The main polymerization products of the CPB samples are calcium–silicate–hydrogel (C–S–H), calcium–aluminosilicate–hydrogel (C–A–S–H), and aluminosilicate crystals such as quartz, albite, and foshagite. These products are intertwined and filled in the internal pores of the CPB, enabling the pore contents to decrease and the interiors of the CPB samples to gradually connect into a whole. In this way, the compressive strength is increased.

Strength, Microstructure, and Deformation Behavior of Frozen Cemented Tailing Material

Cemented paste backfill (CPB) is a novel cementitious construction material that is used extensively for underground mine support and/or mine waste management worldwide. CPB consists of a mix of tailings (mine waste), water, and binder. In other words, tailings are transformed into construction materials. Key engineering properties required for the geotechnical design of CPB structures include strength and deformation behavior. However, there is a paucity of technical data and information about the effect of sub-zero temperatures on these properties. This paper presents an experimental study that focuses on the investigation of the influence of sub-zero curing temperatures on the strength, deformation behavior, and microstructure (e.g., pore structure, porosity, and binder hydration products) of CPB. Several CPB samples with various combinations of compositions (e.g., binder type, cement amount, and water content) cured at different temperatures (sub-zero and room temperatures) and times (7–90 days) are tested with regard to strength, stress–strain behavior, and microstructural characteristics. It is found that frozen CPB (FCPB) exhibits remarkable strength compared with unfrozen CPB and has a great resemblance to frozen soil. No obvious peak stress is observed from FCPB samples during compression, and strain hardening phenomena are commonly seen after the initial yield point. Factors that may affect the behavior of FCPB are thoroughly examined. Binder contents and types are found to be irrelevant; in contrast, water content plays a dominant role. This negligible effect of binder on the properties of FCPB is due to the inhibition of the binder hydration by sub-zero curing temperatures. FCPBs show coarser pore structure than unfrozen CPBs. The results obtained in this study have significant practical engineering applications for mines located in permafrost or cold regions.