Cemented Paste Backfill Research Articles

Recycling Dam Tailings as Cemented Mine Backfill: Mechanical and Geotechnical Properties

As a result of developing technology and scientific studies, employing dam tailings as critical raw material and vital economic reserve has become widespread recently. Employing dam tailings as a main ingredient of CPB (cemented paste backfill) can offer benefits to mining operations. This study deals with the use of dam tailings in CPB, considering the mechanical and geotechnical aspects. CPB was prepared at fixed solid and cement contents (72%, and 5%, respectively) and tested for different cure ages varying from 3 to 56 days. The results disclosed that the strength of filling increased over time, with the exception of 56-day cured CPB having high sulfur minerals where strength decreased sharply. The reasons behind these strength surges could be clarified by CPB’s basicity, which quickens the hydration of cement. Voids between tailings grains are also occupied by hydration products, resulting in the high strengths. Due to the fact that higher sulfate contents can cause lower pH values within CPB, this is one of the factors that should be considered for the backfill’s strength performance. The cement tends to increase the backfill’s pH in short term, but pH of long-term cured backfills decreases because of dam tailings which is inclined to acid formations and erosions. This is a sign that the deformation properties of CPB are deteriorated. Depending on curing time, CPB’s water content and void ratio decrease, but their surface areas increase. The resulting data will endow to better apprehend the effects of dam tailings on CPB quality integrating cost and quality.

Wear law of Q345 steel under the abrasion–corrosion synergistic effect of cemented paste backfill

Excessive pipe wear affects the continuity and safety of the delivery of cemented paste backfill (CPB). However, the dominant factors affecting the wear of CPB transportation pipelines are not well understood. The goal of this study is to determine the wear law of the Q345 steel pipeline under the abrasion–corrosion synergistic effect of CPB at varying mass fractions (76–82%), flow velocities (1–2.5 m/s), and rheological parameters. A mini cathodic protection system was installed in the slurry pot tester to simultaneously acquire the total wear and pure abrasion, while pure corrosion was obtained via immersion testing. The results indicate that the total wear and pure abrasion exhibit a power-law increase according to flow velocity and grow exponentially as the CPB mass fraction increases. CPB with increasing yield stress and plastic viscosity leads to an exponential growth in the total wear and pure abrasion. However, a higher solid fraction not exceeding a certain critical value effectively alleviates pipe wear and resistance. In most cases, the synergistic effect of abrasion–corrosion contributed to more than 50% of the total wear. CPB mass fraction and the abrasion-corrosion synergistic effect are the dominant factors affecting the total wear of the CPB-transporting pipeline and should be properly controlled in practice. CPB with a solid fraction ranging between 76 and 78% at a flow velocity of 1.57 m/s and pipelines made of corrosion-resistant materials are recommended for the mine of interest. The findings are conducive to the selection of appropriate pipeline materials and CPB transportation parameters.

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

The Energy Dissipation Mechanism and Damage Constitutive Model of Roof–CPB–Floor (RCF) Layered Composite Materials

The stability of composite material that is composed of roof rock, cemented paste backfill (CPB), and floor rock has an important impact on safe mining within metal mines. In order to explore the mechanical properties, acoustic emission (AE), energy dissipation, and damage evolution of roof–CPB–floor (RCF) layered composite materials, uniaxial compression (loading rate 0.02 mm/min) AE tests on RCF materials with different CPB height ratios were performed. The test results show that: (1) the uniaxial compressive strength (UCS) and elastic modulus (ER) of the RCF material were lower than those of the roof or floor rock and higher than that of the CPB. With the increase in the CPB’s height ratio from 0.2 to 0.7, the UCS and the ER decreased from 18.42 MPa to 10.08 MPa and 3.15 GPa to 1.79 GPa, respectively, and the peak strain first decreased from 0.695 to 0.510 and then increased from 0.510 to 0.595. The UCS increased as a polynomial function with the increase in the ER. (2) The AE ring count first increased slowly, then increased rapidly, and finally maintained a high-speed increase. The AE cumulative ring count at the peak point decreased with the increase in the CPB height ratio. The energy dissipation showed that the elastic energy UE accumulated slowly at first, then the dissipated energy UD increased, and finally the UE decreased and the UD increased almost linearly. The UT, UE, UD, UE–UT ratio and UD–UT ratio showed a decreasing trend, and the UE–UD ratio showed an increasing trend at the peak point with the increase in the CPB height ratio. (3) Two damage constitutive models were established based on the AE ring count and energy principle. The damage evolution process of RCF materials can be divided into three stages: the slow damage accumulation stage, stable damage growth stage, and rapid damage accumulation stage.

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.

Mechanical properties, crack evolution and damage characteristics of prefabricated fractured cemented paste backfill under uniaxial compression

The existence of joints and fractures will inevitably affect the mechanical behavior and crack propagation law of the backfill, and then degrade the stability and accelerate the damage evolution of the backfill. Thus, in this study, the uniaxial compressive strength (UCS) tests and acoustic emission (AE) monitoring were carried out for prefabricated fractured (PF) cemented paste backfill (CPB or FCPB) with different dip angles (0, 30, 45, 60, 90°) respectively. The results showed that: 1) The existence of PF collapsed the mechanical properties of the backfill. The UCS and elastic modulus of FCPB samples first decreased and then increased with the increase of PF dip angle, and the deterioration of the 30° FCPB sample was the most serious scenario. 2) Apart from the stress–strain curve of the traditional CPB sample, FCPB sample (except 90°) was a bimodal curve. The self-strengthening characteristics caused by the compression closure of PF led to the continuous upward trend of stress after reaching the first peak and then the second peak. 3) The crack of the FCPB sample usually originated at the tip of PF, and the far-field crack was easy to expand to PF. The PF was conducive to crack development propagation, resulting in macro failure. The failure modes of CPB and FCPB samples were shear failures and tensile failure respectively (shear crack and tensile crack were significantly affected by PF dip angle). 4) The AE ringing count rate and energy rate of FCPB samples (except 90°) usually surged twice, which corresponded to the vicinity of the two peak points of the stress–strain curve of FCPB samples. 5) A piecewise statistical damage constitutive model considering initial damage was established, which could fully reflect the bimodal stress–strain curve characteristics of FCPB samples. The damage evolution law of the FCPB samples obtained from this was significantly affected by PF dip angle. The damage curves of CPB and FCPB (60, 90°) increased approximately in S-shape, while the damage curves of other FCPB increased continuously in the first peak stage and then entered the stable development- accelerated damage-failure stage of the second peak stage. The findings of the study can serve as a theoretical foundation for analyzing the stability of backfill with geological defects such as joints and fractures.

Optimization of Parameters for Rheological Properties and Strength of Cemented Paste Backfill Blended with Coarse Aggregates

Cemented paste backfill (CPB) technology is widely used for environmental protection and underground goaf treatment. The influences of solid concentration, coarse aggregates dosage, and cement dosage on the rheological properties and compressive strength of CPB blended with coarse aggregates (CA-CPB) are investigated through three-factor and four-level orthogonal experiments. The dynamic shear stress and plastic viscosity are selected to characterize the rheological properties of CA-CPB. The uniaxial compressive strength (UCS) is used to describe the compressive strength. The effect of each factor on rheological properties is different from that on UCS. The most significant influences on rheological properties and UCS are solid concentration and cement dosage, respectively. The optimal levels of each factor for rheological properties and UCS are different, resulting in different optimal combinations obtained through range analysis. Therefore, the overall desirability function approach is employed to perform multiple response optimization. The optimal parameters for high fluidity and strength obtained provide valuable information for the CA-CPB process in the Chifeng Baiyinnuoer Lead and Zinc Mine.

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.

Experimental Study on Direct Tensile Properties of Cemented Paste Backfill

Cemented paste backfill (CPB) has been increasingly utilized in mines for efficient mineral obtaining and regional ground support. To guarantee the work performance, the mechanical properties of CPB have long been a topic of study among researchers. But the research progress on the tensile strength of CPB is limited, mainly because of the lack of an appropriate test method due to the low tensile strength of CPB. Therefore, instead of the conventional splitting indirect tensile strength test method, a new direct tension test method, which utilizes the specifically designed compression to tension load converter (CTLC) and dog-bone-shaped specimen, has been applied to study the direct tensile properties of CPB. In this study, the direct tensile strength (DTS) of 47 CPB mix designs were measured using CTLC, and the unconfined compressive strength (UCS) of the corresponding mix design was also tested. The experimental results showed that the increase in the binder content, solid mass content, and curing period led to higher CPB direct tensile strength, and the DTS of CPB was most sensitive to the binder content. Furthermore, the influence of the slurry mass solid content on the tensile strength of CPB was not linear. The influence of the binder content became increasingly notable with the increase in the solid content, especially if the binder content exceeded 75%. The effect of the curing period was found to be rather marginal due to the decreasing amount of un-hydrated cementitious materials left with the increase of the curing period. Overall, the DTS generated using dog-bone specimens and the CTLC apparatus are valid for better mine backfill designs. Finally, a linear correlative between UCS and DTS with a formula in the form of σDT (DTS) = 0.171 σc (UCS) was obtained, and the correlation was sufficient for further calculation of DTS using measured UCS.

A Support Vector Machine and Particle Swarm Optimization Based Model for Cemented Tailings Backfill Materials Strength Prediction.

This study aimed to investigate the feasibility of using a model based on particle swarm optimization (PSO) and support vector machine (SVM) to predict the unconfined compressive strength (UCS) of cemented paste backfill (CTB). The dataset was built based on the experimental UCS values. Results revealed that the categorized randomly segmentation was a suitable approach to establish the training set. The PSO performed well in the SVM hyperparameters tuning; the optimal hyperparameters for the SVM to predict the UCS of CTB in this study were C = 71.923, ε = 0.0625, and γ = 0.195. The established model showed a high accuracy and efficiency on the prediction work. The R2 value was 0.97 and the MSE value was 0.0044. It was concluded that the model was feasible to predict the UCS of CTB with high accuracy and efficiency. In the future, the accuracy and robustness of the prediction model will be further improved as the size of the dataset continues to grow.

Effective reuse of red mud as supplementary material in cemented paste backfill: Durability and environmental impact

Red mud (RM) is a potential supplementary backfill material. However, little is known about cemented paste backfill (CPB) preparation from reused RM. Here, the feasibility of Bayer RM in CPB technology is discussed to expand the utilization of solid waste. With Bayer RM, Fly ash (FA), and cement as raw materials, the strength performance of Bayer RM in cemented paste backfill (RM-CPB) was evaluated by the orthogonal experiment method, and the optimal ratio of RM-CPB was determined. The effects of slurry concentration, mixing ratio of RM to FA, and the cement dosage on uniaxial compressive strength (UCS) were studied. Its durability, microstructure, permeability, and environmental properties were investigated. The experimental results show that the strength of the optimum proportion reached 1.25 MPa and 2.37 MPa after curing for 3 d and 28 d respectively and meet the mine design standard when the ratio of RM-CPB is: 60% of the slurry concentration, the RM: FA is 3:2, and the dosage of cement is 5%. RM-CPB material has good durability, and the main hydration products are C-S-H gel, ettringite, and gmelinite, which is conducive to the development of UCS of the backfill material. Meanwhile, the permeability k20 of RM-CPB is only 6.005 × 10-6 cm/s, indicating that the material has few internal pores, which can effectively prevent external water intrusion. The leaching test results showed that both the heavy metal concentration and pH value of the leachate were within the range specified in the Chinese standard (DZ/T 0290–2015), and it was found that the effect of the three ion leaching tests is successive: toxicity leaching test > immersion test > eluviation test. The comprehensive analysis found that the reuse of Bayer RM as a supplementary cemented paste backfill material provides a new idea for the large-scale utilization of industrial solid waste.

Kalsitik ve dolomitik kireçtaşlarının çimentolu macun dolgunun çevresel davranışına etkisi

Bu çalışmada, çimentolu macun dolgu (ÇMD) karışımında sülfürlü maden atığı (S-MA) yerine ikame (ağırlıkça %10) olarak doğal alkali malzemelerin (kalsitik kireçtaşı: KK ve dolomitik kireçtaşı: DK) kullanılmasının ÇMD’nin uzun dönem çevresel davranışına etkileri araştırılmıştır. Bu amaçla, ÇMD numuneleri 360 güne kadar dinamik tank liçi testlerine tabi tutulmuş ve elde edilen sızıntı suları üzerinde pH, sülfat (SO42-) ve ağır metal (Cu-As-Pb-Cd-Co-Ni-Cr) analizleri gerçekleştirilmiştir. Ayrıca, mineraloji ve mikroyapı özelliklerinin ÇMD’nin çevresel davranışına etkisi X-ışınları difraktometre ve porozite testleri ile incelenmiştir. Bulgular, KK ve DK kullanımı ile sızıntı suyu pH’ının alkali seviyelerde seyrettiğini ve SO42- salınımının önemli ölçüde azaltıldığını göstermiştir. Dahası, KK ve DK ikameli ÇMD numunelerindeki daha yoğun mikroyapı ÇMD'den ağır metallerin (Cu, Mo ve Pb hariç) salınımının engellenmesine veya büyük ölçüde azaltılmasına katkı sağlamıştır. Sonuçlar, ÇMD’nin maliyet ve mekanik özelliklerinin yanısıra yeraltı suyu kirliliği üzerindeki etkisinin de dikkatle değerlendirilmesinin gerektiğini ortaya koymaktadır.

Temperature Effect on Mohr–Coulomb’s Effective Strength Parameters of Paste Backfill

In-stope paste backfill monitoring at different mine sites showed anomalous increase in total stress during rest periods. One of the explanations according to a recent laboratory- model experiment was attributed to volumetric expansion caused by temperature increase within the backfill. This paper extends the understanding whether the Mohr–Coulomb’s effective strength parameters are affected by such temperature increase. The effects are explained through evaluating the apparent cohesion and the effective internal and interfacial friction angles under different temperature conditions. A series of modified direct shear tests were performed on saturated specimens under three controlled temperature levels: 25°C, 50°C, and 70°C. The specimens consist of cemented paste backfill and uncemented paste backfill. The results show that the effective internal and the interfacial friction angles increase as the temperature increases, depending on the type of material and the shearing condition, whereas the temperature increase does not significantly affect the apparent cohesion. The findings serve as a reference for engineers and academics in explaining the stress anomaly and to better understand the shear behavior of paste backfill under different temperature conditions for mine stope backfill design.

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.

Strength and microstructural evolution of alkali-activated slag-based cemented paste backfill: Coupled effects of activator composition and temperature

The activator concentration/silica modulus and curing temperature play critical roles in the engineering performance of alkali-activated slag-based cemented paste backfill (AAS-CPB). Different types of AAS-CPB samples, as well as CPBs made of OPC, were tested at different curing times and temperatures (10 °C, 20 °C, 30 °C, and 40 °C). The results show that the strength of AAS-CPB is more sensitive to changes in curing temperature, and the strength of AAS-CPB is consistently higher than that of CPB made of OPC. Moreover, the strength evolution of AAS-CPB is strongly affected by the coupled effect of curing temperature and activator concentration/silica modulus. An increased activator concentration and a reduced silica modulus can improve the early strength of AAS-CPB under a low curing temperature, but it can also weaken the improvement in the late strength of AAS-CPB under warmer curing temperatures. These findings could contribute to successful application of AAS binder to the mine backfill operation.

A binder prepared by low-reactivity blast furnace slags for cemented paste backfill: Influence of super-fine fly ash and chemical additives

Alternative binders for cemented paste backfill (CPB) are necessary to be prepared considering the high cost and environmental footprint of ordinary Portland cement (OPC). This study focuses on the preparation of a binder using low-reactivity blast furnace slag (BFS). Superfine fly ash (SFA) and chemical additives (aluminum sulfate, AlS and carbide slag, CC) are used to modify the binder properties. Both SFA and chemical additives could promote the binder reaction with the formation of more reaction products. The pore structure was then refined; thereby higher compressive strength was observed. Krstulovic-Dabic (K-D) model was used to characterize the hydration process and all binders hydration mechanism was ‘NG-I-D’. The synergistic effect of SFA, AlS, and CC showed the best performance, the compressive strength of the CPB samples could reach 0.24 MPa and 2.73 MPa at 3 and 28 days using the optimal proportion. The excellent performance can be attributed to the physical and chemical effects of the coupling actions of SFA and chemical additives.

Stability Evaluation of Layered Backfill Considering Filling Interval, Backfill Strength and Creep Behavior

Cemented paste backfill (CPB) is the primary solution to improving the safety of continuous mining. The interaction between rock mass and backfill is an important indicator of backfill stability. The creep behavior of weak rock mass is an essential factor, which causes the evolution of stresses and displacements in the backfill stope. In this paper, numerical models were constructed to analyze the interactions between rock mass and backfill by considering the creep behavior of the rock mass, filling interval, and backfill strength. The numerical simulation results showed the effects of different parameters, including the number of backfilling layers, filling interval time (FIT), and backfill strength under creep behavior on stress, displacements, and plastic deformation. The horizontal displacement near the mid-height and vertical displacement at the top of the backfilled stope is the largest compared to layered backfilling. The stress within the backfilled stope is smallest when the stope is filled in a single layer. With increasing FIT, stress in the backfilled stope decreases. FIT mainly affected the horizontal displacement of the stope. The stresses on the stope bottom decrease when the strength of the middle-backfilled stope decreases. Overall, this study provides important insights for understanding the creep behavior of rock mass in underground backfilling practices.

Strength Analysis and Optimization of Alkali Activated Slag Backfills Through Response Surface Methodology

The significant difference in water-to-binder ratio, activator type and concentration between alkali-activated slag (AAS) paste/mortar/concrete and AAS-based cemented paste backfill (AAS-CPB) means that previous results related to the properties and mix optimization of AAS materials cannot be directly translated to AAS-CPB. This study statistically identifies the effect of key influential variables such as silicate modulus, slag fineness and activator concentration on 3- and 28 day unconfined compressive strength (UCS) of AAS-CPB by central composite design (CCD) established in response surface methodology (RSM). In this study, the prominence of independent variables and their relations are investigated by using ANOVA (analysis of variance) having a significant level of 0.05. ANOVA results certify that there is a strong link between the level of variable contribution on UCS performance of AAS-CPB and curing age. Obviously, silicate modulus and activator concentration are the most major variables influencing UCS at 3 and 28 days, respectively. Increased fineness of slag and higher pH of pore solution enhance 3 day UCS, but restrain the further hydration of unreacted slag and subsequent the gain in strength at advanced curing ages. The combination of independent variables of silicate modulus (0.295), slag fineness (12630.2), activator concentration (0.45) gives the optimum responses.

Modification of carbonate-activated binder for lead-zinc mine tailings based cemented paste backfill

CPB promotes a green development of the mining industry. At the same time, the high cost of OPC limits the large-scale application of CPB. This study aimed to use carbonate-activated binders as cementitious materials in LZT based CPB. The binder was modified by CLDH and/or HM when considering the carbonate-activated binder's low reaction rate and bad performance. The effect of 3–5 wt% CLDH and 0.5–1 wt% HM on the reaction kinetics and phase assembles of Na2CO3-activated slag was investigated via isothermal calorimetry, XRD, and TG analysis. Flowability, setting time, and compressive strength of CPB samples were used to assess the feasibility of the binder in CPB. The immobilization effect and leaching mechanism of heavy metals from the CPB samples were then evaluated via TCLP, sequential extraction test, and semi-dynamic leaching. The incorporation of CLDH and HM accelerated binder reaction through consuming CO32−. The coupling addition of 3 wt% CLDH and 0.5 HM presented the best performance, reaching about 2.29 MPa at 28 days. This value was higher than OPC-based CPB samples by around 10%.

Pore structure, mechanical behavior and damage evolution of cemented paste backfill

In this paper, the internal pore structure and mechanical properties of cemented paste backfill (CPB) with different mix proportions are studied by low field nuclear magnetic resonance (NMR) and unconfined compressive strength (UCS) test, and the relationship between UCS, pore structure characteristics and curing time is quantitatively characterized. The following conclusions are obtained: (1) The internal pores of CPB are divided into micropores, secondary pores, and macropores, among which secondary pores account for the largest proportion, accounting for about 70% of the total pores. The proportion of macropores is inversely proportional to the UCS, while the proportion of micropores is proportional to the UCS. (2) The porosity of CPB decreases with the increase of curing time, and UCS increases with the increase of curing time. The curing time has an exponential function relationship with porosity. UCS decreases exponentially with the increase of porosity. (3) A damage model of CPB is established considering the initial pore damage, which is highly consistent with the experimental results. The total damage evolution curve presents an “S" type distribution. The total damage change rate evolution curve showed a normal distribution.