Cemented Paste Backfill Mixtures Research Articles

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.

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

This study investigates the time-dependent rheological behavior of cemented paste backfill (CPB) that contains calcined clay as a binder, particularly with LC3 (Limestone Calcined Clay Cement) compositions, using two different PCEs (Polycarboxylate Ether) superplasticizers. Rheological measurements have been conducted on four different mix designs using the Bingham model to describe the CPB mixtures. Both yield stress and plastic viscosity have been reported, and the impact of the admixture on these parameters has been investigated. Unconfined compressive strength (UCS) was measured over 182 days for all mix designs. Both admixtures showed better workability in all cases, with significantly improved yield stress and plastic viscosity compared to the reference, while showing little to no negative impact on strength over time. This study highlights that both from a binder and an admixture point of view, relevant to the industry, these calcined clay systems are ready to be used in a CPB and could make a significant impact on the sustainability of a mining operation in the near future.

Strength and suction development of nano-cemented paste tailings materials

This paper presents an experimental study of the strength and suction development of cemented paste backfill (CPB), which is an innovative cementitious construction material for mining (made by recycling mine waste into a construction material), and modified with nanoparticle (NP) additives. The effects of different amounts of four types of NP additives, including nano-silica (SiO2), nano-calcium carbonate (CaCO3), nano-iron oxide (Fe2O3), and nano-aluminum oxide (Al2O3), on the key engineering properties of CPB are investigated. An ether-based polycarboxylate superplasticizer (SP) is added to the backfill to help the NPs to better disperse in the mixture. Ordinary Portland cement is used as the binder in the CPB mixture. Uniaxial compressive tests (UCS) are conducted to determine the strength of the CPB, while suction monitoring experiments are performed to evaluate changes in suction with time. To understand the effects of the NP additives, different microstructural analyses and tests, including thermal analyses (thermogravimetry (TG), differential thermogravimetry (DTG)), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD) are conducted on the nano-CPB and the cement paste of nano-CPB. The results indicate that the addition of NP additives in the absence of SP results in lower strength due to high likelihood of agglomeration. In contrast, samples with SP and NP additives show a higher UCS and more suction than the control sample at the early ages of curing. It has been observed that the addition of NP additives results in the generation of more hydration products which enhance the interparticle friction and packing density of the CPB structure. Higher strength is obtained by increasing the SP content (0.25%) with the same NP content (1%). Enhancement of the strength of CPB and increase in suction, particularly at early ages, can have great importance in speeding up the mining cycle and thus increasing mining productivity, which is obviously associated with financial benefits to the mine.

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.

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.

The Role of Rheological Additives on Fresh and Hardened Properties of Cemented Paste Backfill.

Cemented paste backfill (CPB) has become a significant structural material in most mines across the world. In this study, the effects of chemical rheological additives including viscosity modifying agent (i.e., polyacrylamide) and polycarboxylate superplasticizer (PCE) on fresh and hardened properties of CPB with different water-to-solid (W/S) ratios and water-to-cement (W/C) ratios were investigated. The microstructure of CPB specimens was also characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and backscattered electron image (SEM-BSE). The obtained results indicate that PAM (polyacrylamide) dosage and W/S are the most significant parameters influencing the workability of fresh CPB mixtures. For the hardened CPB specimens, the decreasing W/S ratio leads to higher flexural and compressive strength values and lower dry shrinkage strains. The interfacial transition zone (ITZ) between the cement matrix and the tailings sand was also observed to be narrower, with fewer micro cracks and capillary pores. Meanwhile, the existence of PAM decreased the number of hydration products and retarded the hydration reaction. Overall, the CPBs with high W/C ratios (i.e., 1.0 and 1.2), low W/S ratios (i.e., 0.3), and moderate amounts of rheological additives (i.e., 0.05% PAM and 1.0% PCE) have excellent fresh and hardened properties. The findings of this study contribute to better optimization of CPB mixtures in backfill construction, bringing benefits of low costs and low environmental impacts.

Influence of silica fume on mechanical property of cemented paste backfill

The cemented paste backfill (CPB) method, which is the most preferred method for tailings storage, is one of the most used methods for the disposal of mine tailings. However, the high rate of cement usage increases the costs. In this study, whether silica fume (SF), which is a pozzolanic material, can be used as a substitute instead of cement was investigated based on mechanical parameters or not. As a result of the experiments, it was determined that SF substituted for portland cement (PC) increased the strength of paste backfill mixtures prepared in a certain cement ratio. In addition, it was determined that SF substitution in CPB increased the durability of mixtures against sulphate attacks as it did in concrete. With the use of SF, savings of up to 20% were achieved in the amount and cost of cement used in CPB. Besides, using it without the pulverizing process required for pozzolanic materials used in other studies had a positive effect in terms of time and cost. Moreover, the use of SF in CPB mixtures resulted in less energy use and less greenhouse gas emissions, and a reduction of environmental pollution caused by SF tailings.

Specific Mixing Energy of Cemented Paste Backfill, Part I: Laboratory Determination and Influence on the Consistency

Slump determination is widely used to assess the consistency and transportability of fresh cemented paste backfill (CPB). CPB consistency can depend on the mixing procedure for CPB preparation. In this paper, a method was developed to determine the specific mixing energy (SME) that is dissipated during the preparation of CPB mixtures and to analyze its effect on CPB consistency. For this purpose, CPB recipes were prepared using two tailings and the mixing parameters (mixing time and speed and load mass) were successively varied. SME was determined for each mixture using a power meter equipped with an energy recording system mounted on a laboratory Omcan mixer. Slump was also determined for each mixture. A semi-empirical model was then developed to predict SME as a function of the mixing parameters. Results showed that predicted SME compared well with measured SME during CPB preparation. Results also showed that slump increased with increasing SME. The influence of SME on the rheological and mechanical properties of CPB and practical applications are presented in a companion paper.

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.

Temperature induced changes in the behaviour of cementing fine-grained soils under dynamic loadings

ABSTRACT Cemented paste backfill (CPB) has been extensively used in the mine industry to backfill underground mine cavities for ground support and/or tailings management. Once placed in mine underground cavities, the geotechnical and liquefaction response of the CPB under dynamic (cyclic) loadings is a key design concern in mine backfilling. Moreover, fresh CPB might be exposed to several sources of heat that might affect its cyclic behaviour and liquefaction potential. This manuscript presents findings of assessing the effect of backfill temperature on its geotechnical and liquefaction response to cyclic loading by using shaking table. CPB mixtures were prepared under different temperatures, poured into a flexible laminar shear box, cured (under the same mixing temperature) for 2.5 hours, and then exposed to cyclic loading using 1-D Shaking table. Obtained results illustrate that CPB prepared and cured under the temperature of 20°C can be prone to liquefaction under the studied loading conditions. However, CPB prepared and cured below a temperature of 35°C is resistant to liquefaction. These results provide better comprehension of the effect of backfill temperature on the cyclic behaviour of CPB, and thus assist in designing more efficient CPB structures.

Effect of construction and demolition waste on the long-term geo-environmental behaviour of cemented paste backfill

The construction and demolition waste (CDW) could be used as backfill material to fill the voids created during the ore production in underground mining. However, there is a need to clarify the impact of CDW on groundwater pollution when it is used as backfill material in cemented paste backfill (CPB) of sulphide-rich tailings (S-rT). This study presents the influence of CDW on the long-term geo-environmental behaviour of CPB samples (CPBs) when used as replacement (10 wt.%) to S-rT. For this reason, the dynamic-tank leaching test was conducted on CPBs and pH, conductivity (Ec), sulphate (SO42−) and heavy metals (HMs) analyses were executed for leachates over 30–360 days of leaching period. The effects of mineralogy and microstructure on the geo-environmental behaviour of CPBs were also analysed via X-ray fluorescence (XRD) and mercury intrusion porosimeter (MIP). The utilisation of CDW in CPB mixtures was found to reduce the SO42− release (up to 13.89%), neutralise the acid generated and lower the Ec (up to 22.16%). Furthermore, the HMs releases (except As, Cu and Zn) were prevented (Ni and Cr) or reduced up to 92%, which is compatible with the improved CPB microstructure. Only the release of arsenic (As) exceeded the limit value for groundwater in CPB of CDW leachate. These findings suggest that not only the cost, strength and stability but also the impact on groundwater pollution should be considered when disposing of CDW as CPB material in underground voids.

Chemically induced changes in the geotechnical response of cementing paste backfill in shaking table test

Abstract Cemented paste backfill (CPB) is extensively used for underground mine support and/or tailings management. However, CPB behavior under cyclic loadings might be affected by the chemistry of its pore-water, which often contains sulphate ions. Till today, no studies have addressed the effect of sulphate on the response of CPB to cyclic loadings by using shaking table technique. This study presents new findings of assessing the effect of the sulphate in the pore water of CPB on its geotechnical response to cyclic loading by using shaking table. CPB mixtures were prepared (with and without sulphate), poured into a flexible laminar shear box, cured to 4 h, and then exposed to cyclic loading using one-dimensional (1D) shaking table. Several parameters (e.g. pore water pressure, settlement, lateral deformation, acceleration, electrical conductivity, effective stress, and liquefaction susceptibility) were monitored or determined before, during, and after shaking. Obtained results indicate that the sulphate-bearing CPB cured to 4 h can be prone to liquefaction under the studied conditions. However, sulphate-free CPB samples are resistant to liquefaction. These results are expected to contribute to a better understanding of the effect of water chemistry on the cyclic behavior of CPB, consequently enhancing the cost-effective design of CPB structures.

Evaluation of geochemical behaviour of flooded cemented paste backfill of sulphide-rich tailings by dynamic-tank leaching test

ABSTRACT This research elucidates the geochemical behaviour of cemented paste backfill (CPB) of sulphide-rich tailings (S-rT). The dynamic-tank leaching test was performed on the CPBs for up to 360 days. The CPBs with the alkaline industrial by-products (AIPs) produced relatively lower acidity, Ec and SO4 2- than the Control. The AIPs replacement appeared to considerably mitigate the release of heavy metals (HMs) including As. Only Mo and As in CPBs of AIPs exceeded the limit-values for ground-water. These findings demonstrated that a suitable CPB mixture design to control the release of all HMs in CPB is of practical importance for ground-water quality.

Effect of temperature on time-dependent rheological and compressive strength of fresh cemented paste backfill containing flocculants

Temperature significantly affects the transportability and strength of fresh cemented paste backfill (CPB). In this study, experiments are performed to investigate the effect of temperature on the time-dependent fluidity and compressive strength of CPB samples containing different flocculants dosages (anionic-type polyacrylamide). Rheological tests are conducted on fresh CPB samples containing 0, 55, 75, and 85 g/t flocculants, which are then are cured for 0, 20, 40 and 60 min, respectively. Subsequently, mechanical tests are performed on the CPB samples cured at 2 °C, 20 °C and 50 °C for 3, 7, and 28 d, respectively. Moreover, microstructural analysis and zeta potential measurements are performed to evaluate the effect of curing temperature and flocculants dosage on the microstructure and zeta potential of fresh CPB mixtures. The results show that the time-dependent rheological of the fresh CPB mixtures are significantly affected by the curing temperature and flocculants dosage. Both the yield stress and viscosity increase steadily as the curing time elapses, and an increase in the curing temperature and flocculants dosage results in a higher yield stress and viscosity. The uniaxial compressive strength of the CPB samples is enhanced by the curing temperature but decrease with increasing flocculants dosage. The CPB samples with flocculants exhibit a looser and more heterogeneous structure than the flocculants-free CPB samples. The findings of this study provide guidance for the design and application of CPB in deep mines.

Multi-objective mixture design of cemented paste backfill using particle swarm optimisation algorithm

In order to achieve a successful cemented paste backfill (CPB) mixture design, multiple project requirements such as strength, flowability and cost should be met. For this achievement, the key design parameters, solid content (SD) and cement percentage (C), should be well adjusted. With increasing the amount of cement in the mixture, CPB strength and production cost increase together, whereas the workability decreases. In order to reduce the cost, more tailings can be added while keeping the cement amount the same but this will reduce both strength and workability. Therefore, CPB design is in fact a multi-objective optimisation problem. In this study, the particle swarm optimisation (PSO) algorithm is used to design CPB mixture meeting multiple objectives. PSO identifies the optimum set of SD and C yielding in desired strength and workability with a minimum cost. The proposed workflow can be a useful and practical for multiple decision making where CPB designers face strength-workability-cost paradox. In addition to reducing the number of trial experiments, the multi objective mixture design of CPB also provides the optimum use of materials to reduce the incurred costs and ensure cleaner and more sustainable production.

Rheological Properties of Cemented Paste Backfill with Alkali-Activated Slag

This study investigates the time-dependent rheological behavior of cemented paste backfill (CPB) that contains alkali-activated slag (AAS) as a binder. Rheological measurements with the controlled shear strain method have been conducted on various AAS-CPB samples with different binder contents, silicate modulus (Ms: SiO2/Na2O molar ratio), fineness of slag and curing temperatures. The Bingham model afforded a good fit to all of the CPB mixtures. The results show that AAS-CPB samples with high binder content demonstrate a more rapid rate of gain in yield stress and plastic viscosity. AAS-CPB also shows better rheological behavior than CPB samples made up of ordinary Portland cement (OPC) at identical binder contents. It is found that increasing Ms yields lower yield stress and plastic viscosity and the rate of gain in these parameters. Increases in the fineness of slag has an adverse effect on rheological behavior of AAS-CPB. The rheological behavior of both OPC- and AAS-CPB samples is also strongly enhanced at higher temperatures. AAS-CPB samples are found to be more sensitive to the variation in curing temperatures than OPC-CPB samples with respect to the rate of gain in yield stress and plastic viscosity. As a result, the findings of this study will contribute to well understand the flow and transport features of fresh CPB mixtures under various conditions and their changes with time.

Effects of water content, water type and temperature on the rheological behaviour of slag-cement and fly ash-cement paste backfill

The pumping ability and placement performance of fresh cemented paste backfill (CPB) in underground mined cavities depend on its rheological properties. Hence, it is crucial to understand the rheology of fresh CPB slurry, which is related to CPB mixture design and the temperature underground. This paper presented an experimental study investigating the effects of binder type, content, water chemical properties and content, and temperature, on the rheological properties of CPB material prepared using the tailings of a copper mine in South Australia. Portland cement (PC), a newly released commercially manufactured cement called Minecem (MC) and fly ash (FA) were used as the binders added to the mine tailing materials. Various amounts of two different water types were added to the mixtures in the preparation of backfill material slurry. Six different temperatures ranging from 5 to 60 °C were to investigate the effect of temperature on CPB rheology. Overall, the increasing water content and decreasing temperature lead to lower yield stress. Based on the results obtained from the rheological properties of CPB slurry, it was found that at room temperature (25 °C), with regards to the unconfined compressive strength (UCS) performance, the replacement of 4% PC mixed CPB (28 days UCS 425 kPa) to 3% MC mixed CPB (28 days UCS 519 kPa), reduced the slurry yield stress from 210.7 to 178.5 Pa. The results also showed that the chemical composition of water affects the yield stress of CPB slurry and that MC mitigates the negative effect of mine-processed water (MW) and thus lead to improve the rheological properties of the slurry. However, the results suggested that the rheological properties of a mixture using MC is very sensitive to the water volume and temperature change. Therefore, using MC in backfill requires better quality control in slump mixing.

Evaluation of the neutralization performances of the industrial waste products (IWPs) in sulphide-rich environment of cemented paste backfill

The purpose of this research is to examine the neutralization performances of CaO-rich industrial waste products (IWPs) in the sulphide-rich environment of cemented paste backfill (CPB). A total of 205 CPB samples were prepared by using four different IWPs (type-C fly ash (C-FA), blast furnace slag (BFS), calcitic limestone (CL) and dolomitic limestone (DL)) as 5, 10 and 15 wt% substitute for sulphide-rich tailings. These CPB samples were cured and subjected to the acid (pH) and sulphate (SO42−) tests during 7–360 days of curing periods. MIP and XRD tests were also carried out to understand the generation of acid and sulphate and their effect on CPB stability at 28 and 180 days. The findings indicated that the utilisation of IWPs in CPB mixtures mitigated the acid (up to 58.9% higher pH values) and sulphate (up to 72.1% lower SO42− ion release) production, and enhanced the microstructure (12.43% lower total porosity) of CPBs owing to the neutralization potential, pore-filling effect, pozzolanic and partially binding characteristics of IWPs. It can be inferred from these findings that the IWPs can be suitably utilised as neutralization materials in CPB of sulphide-rich tailings. This in turn allows the mitigation of potential disposal/pollution problems associated with these IWPs.

Effect of Desliming of Tailings on the Fresh and Hardened Properties of Paste Backfill Made from Alkali‐Activated Slag

Cemented paste backfill (CPB) allows environmental friendly management of potentially hazardous tailings generated from milling of nonferrous metal sulphide ores by placing such tailings into the underground mined‐out openings. The components of CPB are tailings, water, and binders. These components significantly affect the physicomechanical, workability, and geotechnical properties of CPB. Ordinary Portland cement (OPC) is the commonly used binder for CPB operations. The effects of the tailings characteristics and OPC are extensively studied in the study area. The beneficial effect of the use of alkali‐activated slags (AASs) on the mechanical and durability properties of CPB of sulphide‐rich tailings has been recently reported. Therefore, this study especially focused on the effect of desliming of the tailings on the workability properties of sulphide‐rich tailings CPB containing AAS besides hardened properties. In this scope, the water‐retention capacities of full (FT) and deslimed tailings (DT) and the workability characteristics of CPB mixtures were studied. DT was found to decrease the water‐retention capacity, leading to denser CPB mixtures. In addition, DT‐AASs usage produced no adverse effect on the workability of fresh CPB materials. LSS‐S (slag activated with liquid sodium silicate) improved the flowability of CPB mixtures owing to its dispersant effect. Desliming also modified the tailing properties by removing fine particles and improved the main geotechnical parameters of CPB.

Effects of coupled sulphate and temperature on internal strain and strength evolution of cemented paste backfill at early age

Cement hydration is a volume reduction reaction which can result in negative pore water pressure while strengthening the structural stiffness of cemented paste backfill (CPB). Both sulphate and temperature significantly affect the hydration process and thus influence the internal volume change and mechanical properties of CPB. The expansive hydration products produced in sulphated CPB may create an increase in volume which subsequently weakens the CPB. This paper presents an experimental study conducted to evaluate the coupled effects of sulphate and curing temperature on the internal strain evolution of early aged CPB. CPB samples of various initial sulphate concentrations (0, 5000 and 25,000 ppm) were prepared and cured at various temperature (20 °C and 35 °C) at early ages (≤7 days). Mechanical tests were conducted on the samples as internal strain was monitored by Fiber Bragg Grating (FBG) sensors. The results indicate that the FBG sensor is sufficiently sensitive to detect the internal strain development of sulphated CPB mixtures during the hydration process. At sulphate concentration of 25,000 ppm, the expansive strain occurred at curing temperature of 35 °C due to the internal expansive force of the expansive materials. The final internal strain value corresponds closely to the strength of the sulphated CPB. As the internal strain of sulphated CPB decreased, the uniaxial compressive strength and tensile strength showed similar trends throughout the experiment. When expansive strain emerged after the initial thermal strain stage, however, there was a higher ratio of uniaxial compressive strength to tensile strength. This phenomenon merits careful consideration in the stability analysis of exposed CPB in underground mines.