Properties Of Cemented Paste Backfill Research Articles

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.

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.

Experimental study on the evolutive shear fracture behaviour and properties of cemented paste backfill

Shear stress prevalence in in-situ cemented paste backfill (CPB) makes understanding mode-II fracture behaviour and properties vital for the mechanical stability of the backfill structure. This study delves into the effect of cement content on CPB's shear fracture behaviour and properties. Results reveal that higher cement content leads to notable changes in load-displacement characteristics under mode-II loading, including steeper pre-peak slopes, higher peak loads, smaller peak-load displacements, and minimal post-peak resistance. However, increased cement content does not linearly enhance fracture properties. Furthermore, this study proposed predictive models to capture the influence of cement content on the evolutive fracture properties.

Effect of submerged curing on properties of cemented paste backfill

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

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.

Experimental study on the effect of fly ash with ammonium salt content on the properties of cemented paste backfill

The wide disposal of fly ash (FA) that contains ammonium is an essential method to realize green backfill mining and resource utilization of solid waste. In this paper, FA containing ammonium with different ammonia contents was simulated by adding NH4HSO4 to the FA. The law and mechanism of influence of ammonia content on the performance of FA-based cemented paste backfill (FA-based CPB) were explored using thorough experimentation, and a maximum ammonia content of FA containing ammonium used in backfill mining was proposed. The results showed that the fresh FA-based CPB slurry could be described by the Herschel–Bulkley model (R2 ≥ 0.991). With the increase in the ammonia content of FA, the yield stress and viscosity of the FA-based CPB slurry increased and the slump value decreased, due to the formation of specific firm bubble bridges between the cement particles, FA, and tiny bubbles and due to the fact that tiny bubbles need more water due to their large specific surface area. In addition, the uniaxial compressive strength (UCS) and elastic modulus of FA-based CPB decreased and the peak strain increased as the ammonia content of FA increased. Specifically, the 28-d UCS of FA-based CPB with ammonia contents of 239, 639, 1139, and 2139 ppm decreased by 12.4 %, 39.5 %, 42.4 %, and 47.0 %, respectively, compared to that of FA-based CPB with ammonia content of 139 ppm. Finally, MIP, SEM, and XRD were utilized to investigate the microstructure of FA-based CPB. Overall, the ammonium-containing FA adversely affected both the flowability and mechanical properties of FA-based CPB. The results provide a reference for the green and efficient use of FA containing ammonium salts.

The effect of coarse aggregate on the bleeding and mechanical properties of cemented paste backfill

The effect of coarse aggregate on the bleeding and mechanical properties of cemented paste backfill

Geomechanical behavior and properties of cemented paste backfill under passive interface loading and their influences on field-scale stability

Geomechanical behavior and properties of cemented paste backfill under passive interface loading and their influences on field-scale stability

Effects of slag-based cementitious material on the mechanical behavior and heavy metal immobilization of mine tailings based cemented paste backfill

Slag-based cementitious material was synthesized from blast furnace slag, clinker, gypsum, and activator to replace cement in cemented paste backfill (CPB). We researched the influence of slag-based cementitious material dosages and curing times on the properties of CPB, including unconfined compressive strength tests, leachate toxicity and chemical speciation of heavy metal as well as microstructural tests and analyses. The results indicated that the addition of slag-based cementitious material improved the compressive strength of the CPB, which attained the compressive strength requirements (≥1.0 MPa) at 28 days. The leachate concentrations of Pb, Cr, Cu, and Cd in CPB decreased as the slag-based cementitious material dosage and curing period increased, which met the standard (GB 5085.3-2007). The dosage of 10% slag-based cementitious material could effectively immobilize the heavy metals in the tailings, and the immobilization performance was similar to that of 20% cement, which indicated the amount of slag-based cementitious material was only half the quantity of cement in CPB. Microstructural analysis showed the hydration products included calcium silicate hydrate, ettringite, and portlandite, which could enhance the bonding force between the tailing grains.

Experimental investigation of fiber content and length on curing time‐dependent mode‐I fracture behavior and properties of cemented paste backfill and implication to engineering design

AbstractThe inclusion of fiber in cemented paste backfill (CPB) can significantly alter the mechanical response of the CPB body. The intrinsic defects in CPB and the potential dynamic loading condition make it necessary to investigate the fracture properties of fiber‐reinforced CPB (FR‐CPB). The mode‐I fracture behavior and properties are crucial to the successful engineering application of FR‐CPB technology used in underground mines. The contribution of fiber length and content to the evolutive mode‐I fracture behavior and properties of FR‐CPB was examined in this study. The results show that the addition of fiber reduces the prepeak stiffness but improves the mode I fracture toughness (KIc), and the improvement in KIc increases with fiber length. In contrast, the initial increase in fiber content (from 0% to 0.5%) benefits the KIc acquisition, while a further increase in fiber content from 0.5% to 0.75% poses a negative influence on the KIc development. Moreover, with the adoption of the cement hydration model, four predictive functions are proposed to describe the contribution of fiber length and content to the development of fracture properties. In addition, KIc is identified as a more reliable fracture property for assessing the immediate ground support role played by the FR‐CPB structure. The findings are helpful when it comes to the determination of the fiber length and content in FR‐CPB design.

Rheological properties of cemented paste backfill and the construction of a prediction model

The Cemented Paste Backfill (CPB) yield stress is a key rheological parameter for paste filling technology, which has significant practical value for pipeline optimization and equipment selection of pipeline conveying systems. However, the slurry yield stress is affected by many factors. In order to accurately analyze and predict the CPB yield stress, this study uses the sparrow search algorithm to optimize the relevance vector machine (SSA-RVM) and proposes the prediction model of SSA-RVM CPB yield stress regression. Based on 136 sets of rheological tests for copper mine, different waste rock/tailing sand ratios, mass concentrations, and water-cement ratios select to predict the yield stress at different training set ratios (78%, 85%, 92%). Compared with the traditional relevance vector machine (RVM) regression model, the SSA-RVM regression prediction model has higher prediction accuracy. In addition, the coefficient of determination R2 of the predicted and true values obtained from the SSA-RVM model increased by 0.0407, 0.0438, and 0.0500 for the training set ratios of 78%, 85%, and 92%, respectively. The results suggested that SSA-RVM can efficiently predict the CPB yield stress, which can be a reference for the design of paste-filled pipe conveying systems.

Evaluation of time-dependent rheological properties of cemented paste backfill incorporating superplasticizer with special focus on thixotropy and static yield stress

Evaluation of time-dependent rheological properties of cemented paste backfill incorporating superplasticizer with special focus on thixotropy and static yield stress

Effect of fly-ash as fine aggregate on the workability and mechanical properties of cemented paste backfill

An experimental study was conducted to investigate the effect of fly-ash(FA) as a fine aggregate on filling performance. The effect of FA content on the gradation distribution and compactness of the dry mixture is tested. Slump, bleeding rate, and unconfined compressive strength (UCS) of cemented waste rock-FA backfill (CWFB) samples were also tested at different FA content, solids content, and cement-sand ratio conditions. Results show that FA as a fine aggregate can effectively improve the mixture gradation performance. Short-term (3d/7d) strength increases with FA content, while long-term (28d) strength and slump first increase and then decrease, reaching a maximum value of 8.58 MPa and 27.4 cm respectively at 30% FA content. The bleeding rate first decreased and then stabilized (about 5.2%) with FA content. The UCS showed higher sensitivity to high solid content. The slump reduction rate of samples with high FA content decreases with solid content. Larger cement content will weaken the fluidity. When the cement-sand ratio increased from 1:6–1:4, the slump decreased from 27.5 cm to 23.5 cm, and the bleeding rate decreased to 4.05%. However, the mechanical properties are significantly improved with cement content. This study has positive implications for recycling the FA.

Fresh and hardened properties of cemented paste backfill: Links to mixing time

Current technical knowledge is insufficient regarding the influence of mixing time on fresh and hardened properties of cemented paste backfill (CPB). This work focused on experimental studies to gain a deeper understanding of the influence of mixing time on the rheological properties (yield stress, viscosity), self-desiccation, permeability and mechanical properties or behavior (strength, deformation behavior) of CPB. A series of CPB specimens were prepared with various mixing times (1, 2, 4, 7, 10, and 15 min) and cured at different times (1, 2, 4, 7, 10 and 15 min) for rheological property testing. Unconfined compressive strength (UCS), hydraulic conductivity and microstructural tests were performed on CPBs that were made with various mixing times and cured for different times (up to 90 days). Monitoring experiments were also carried out on CPBs prepared with various mixing times. The results obtained indicate that the mixing time significantly affects the rheological, mechanical, hydraulic and microstructural properties of CPB. Moreover, the self-desiccation of CPB is a function of the mixing time. A longer mixing time increased the yield stress and decreased the viscosity. The longer mixing time promoted binder dissolution and hydration in the CPB, which increased the amount of hydration products and decreased the volumetric water. Longer mixing time intensified the CPB self-desiccation, which is beneficial for the early age mechanical strength of CPB. CPB specimens made with longer mixing time experienced a higher strength and elastic modulus due to the generation of more cement hydration products and the reduction of the volume of pores in CPB. A longer mixing time reduced the CPB hydraulic conductivity, due to the refinement of the CPB pore structure. This study provides relevant knowledge and technical information that will contribute to the design of more cost-effective and sustainable CPB structures.

Effect of rice husk ash (RHA) dosage on pore structural and mechanical properties of cemented paste backfill

Reducing solid waste emission is the development direction of cleaner production in the future. This paper proposes to use the agricultural solid waste rice husk ash (RHA) as an alternative cementitious material for the underground filling of mines. The pore structure and mechanical properties of cemented paste backfill with different RHA dosages (RCPB) are analyzed. The results reveal that: (1) The pore structure of RCPB is divided into three types: micropores (<0.1 μm), secondary pores (0.1–100 μm), and main pores (>100 μm). The total number of micropores accounts for the largest proportion, followed by secondary pores and main pores. The total volume of secondary pores accounts for the largest proportion, followed by micropores and main pores. (2) The porosity decreases and the UCS increases with the increase of RHA dosage and curing time. The UCS decreases linearly with the increase of RHA dosage. The UCS has a linear negative correlation with porosity. (3) The cracks of RCPB initiated at the yield point, gradually expanded at the peak point, and finally penetrated at the post-peak point. The failure mode of RCPB is mainly a tensile failure, accompanied by a small number of secondary tensile cracks. (4) The hydration products of RCPB are mainly C–S–H and AFt gels. The greater the RHA dosage and CT, the more hydration products, the fewer pores, the greater the strength, and the greater the average gray value. The outcome of this work will afford a new ideas and methods for using solid waste (Rice husk) as backfilling.

Specific Mixing Energy of Cemented Paste Backfill, Part II: Influence on the Rheological and Mechanical Properties and Practical Applications

The rheological properties (yield stress, flow index and infinite dynamic viscosity) and mechanical properties (unconfined compressive strength, UCS) of different cemented paste backfill (CPB) recipes must be determined during the laboratory optimization phase. However, the influence of the mixing procedure on these properties has scarcely been studied so far. The objective of this paper is to assess to what extent these properties depend on the specific mixing energy (SME) for a given type of mixer. CPB recipes were prepared based on two types of tailing (CPB-T1 and CPB-T2, also referred to as T1 and T2) at a fixed solid percentage for each type of tailing using the Omcan laboratory mixer. A mixture of 80% slag and 20% GU was used as a binder. The mixing time and the rotation speed of the mixer were successively varied. For each recipe prepared, we determined the SME, the rheological properties of fresh CPB (at the end of mixing) and the UCS at 7, 28 and 90 days of curing. The results show that yield stress and infinite viscosity decreased when SME increased in an interval going from 0.3 to 3.8 Wh/kg and 0.6 to 6 Wh/kg for CPB-T1 and CPB-T2, respectively. An increasing trend in UCS with increasing SME was also observed. Empirical equations describing the change of the rheological properties with the SME are used to estimate the change in rheological properties of CPB along the distribution system, considering the specific energy dissipation during CPB transportation. A mixing procedure for obtaining CPB mixtures that are representative of CPB deposited in underground mine stopes is suggested for laboratories who currently use a same mixing procedure, irrespective of the variable field specific energy.

Experimental investigation on flow properties of cemented paste backfill through L-pipe and loop-pipe tests

Experimental investigation on flow properties of cemented paste backfill through L-pipe and loop-pipe tests

The rheological, mechanical and heavy metal leaching properties of cemented paste backfill under the influence of anionic polyacrylamide

Anionic polyacrylamide (APAM) has widely been employed in backfill mining to accelerate the sedimentation of fine tailings particles and increase the concentration of tailings slurry. However, APAM inevitably remains in thickened tailings, leading to a nonnegligible influence on the rheological, mechanical, and heavy metal leaching properties of tailings-based cemented paste backfill (CPB). In an effort to solve these issues, the influences of APAM on CPB properties were examined in the present study. Experimental tests such as rheology, uniaxial compressive strength (UCS), toxicity leaching, and microscopy were conducted. The results showed that the presence of APAM first significantly increased the yield stress and viscosity of CPB slurry. APAM slightly improved the early UCS of CPB curing for 7 days but hindered the UCS development of samples cured for 28 days. Moreover, the presence of APAM restrained the hydration reaction, reduced the amounts of hydrated products, increased pore size, and loosed the microstructure of the test samples. Finally, the addition of APAM effectively reduced the leaching of Ag and As, while incremented that of Cu and slightly affected the leaching of Ba. In sum, these findings look promising for the safe production and environmental protection of the mining industry.

Strength and Ultrasonic Characteristics of Cemented Paste Backfill Incorporating Foaming Agent

This work is a systematic study of the strength and ultrasonic properties of cemented paste backfill incorporating a foaming agent, known as foam-cemented paste backfill (FCPB). Based on determining the optimal admixture contents (foaming stabilizer, thickening agent, and foaming agent), a series of uniaxial compressive strength (UCS) tests were conducted to determine the relationship between the UCS of FCPB and four influencing factors, i.e., cement–tailings ratio (CTR), solid content (SC), curing time (T), and foaming agent content (FC). To analyze the sensitivity of UCS to these four factors, grey relational analysis (GRA) was introduced. Moreover, UCS results were correlated with the corresponding ultrasonic pulse velocity (UPV) parameters. The results indicate that the optimal contents of foaming stabilizer, thickening agent and foaming agent are 0.5%, 0.6%, and 1–3%, respectively. The UCS of FCPB exponentially increases with CTR and SC, while it logarithmically and linearly increases with T and FC, respectively. CTR has the most significant influence, followed by T, SC, and FC. There exists an evidently linear relationship between UPV and UCS of FCPB regardless of CTR, SC, T and FC. These results contribute to understanding the properties of hardened FCPB and to sound designs in practice.

Non-isothermal evolution of mechanical properties, pore structure and self-desiccation of cemented paste backfill

In the field, cemented paste backfill (CPB) structures are subjected to non-isothermal curing conditions. In this study, the non-isothermal strength, pore structure development, and self-desiccation of CPB were investigated. CPB specimens with different types of binders and tailings were prepared and cured under isothermal (room temperature: 20 °C) and field non-isothermal conditions. Unconfined compressive strength (UCS) tests, microstructural tests and analyses as well as monitoring experiments, were conducted on CPB specimens cured over various ages. The obtained results show that the non-isothermal curing condition significantly increases the strength as well as the strength increase rate of the CPB regardless of the type of binder and tailings used. Moreover, the non-isothermal condition leads to more intense self-desiccation of CPB as well as the refinement of the pore structure of CPB due to the generation of more hydration products, such as calcium–silicate–hydrate (C–S–H), in the non-isothermal CPB. It is also found that a mine cavity (stope) backfilled with CPB material made with Portland cement type I (PCI) has a significant advantage over stope backfilled with CPB made with slag/PCI (50%/50%) in terms of strength formation and enhancement of self-desiccation due the difference in the non-isothermal curing conditions. The findings of this study provide insight into the development of the mechanical and microstructure properties as well as self-desiccation of CPB structures when exposed to field thermal curing condtions, thereby contributing to the improvement of mechanical stability and economic performance of future CPB designs. The impact of non-isothermal curing conditions on CPB properties need to be considered in mine backfill design and operations.