Uniaxial Compressive Strength Tests Research Articles

Study on the mechanical properties of anisotropic red sandstone under point load strength test and uniaxial compression strength

The red sandstone of Xiaopu 3# branch Cave in the Yuxi section of the Central Yunnan Water Diversion Project was taken as the research object. The uniaxial compression strength and point load strength test are conducted from the perspectives of vertical and parallel stratifications, respectively, and then the anisotropy of red sandstone was analyzed in detail. The data obtained from the field and laboratory test was analyzed, and the conversion relationship between point load strength index and uniaxial compression strength is a power function under both parallel stratification and vertical stratification. The study results showed that: The mechanical properties of red sandstone have obvious anisotropy. The difference in its mechanical properties is particularly evident in UCS and point load tests and Is(50) and UCS under vertical stratification are significantly greater than Is(50) under parallel stratification. The point load strength correction index m of red sandstone is m = 0.4096 under parallel stratification, and m = 0.4408 under vertical stratification.

Study on mesostructure and stress–strain characteristics of pervious concrete with different aggregate sizes

This work aimed to study the mesostructure and compressive behavior of pervious concrete (PC) with different aggregate sizes, and to explore the mechanism responsible for the resulted performance. The mesostructure of PC was quantitatively evaluated, including the distribution of internal voids, the distribution of aggregates and the thickness of cement paste using image processing technology. In addition, the full stress–strain curve of PC was obtained by the uniaxial compressive strength test, in which the uniaxial stress–strain characteristics and the whole process of compressive failure was assessed. The results show that the larger the particle size of the aggregate, the fewer the number of voids, and the larger the average diameter of voids. The aggregate distribution in PC with different aggregate sizes is different, but is approximately uniformly distributed. The cement paste thickness of the PC studied in this paper ranges from 0.4 to 0.7 mm. With the same cement content and different aggregate composition, the thickness of cement paste gradually decreases with the decrease of aggregate size. It is found that the stress–strain curve of PC has the same change trend as that of ordinary concrete, and it is a biased unimodal curve. Furthermore, the failure of the PC is proved to be a shear failure. During the destruction of PC, the aggregate is also destroyed which is different from the damage of ordinary concrete.

Mechanical properties, pore characteristics and microstructure of modified magnesium slag cemented coal-based solid waste backfill materials: Affected by fly ash addition and curing temperature

The high-temperature, deep-well environment can affect the mechanical properties and long-term stability of modified magnesium slag cemented coal-based solid waste backfill material (MMS-CBM). The purpose of this study was to investigate the effects of fly ash addition (0 %, 10 %, 20 %, 30 % and 40 %) and curing temperature (20 °C, 30 °C and 40 °C) on the mechanical properties, pore characteristics and microstructure of MMS-CBM. Based on this, relevant laboratory tests (uniaxial compressive strength test, pore structure test and microstructure test) were conducted to characterize the influence mechanism of fly ash addition and curing temperature on the performance of MMS-CBM. The results show that the physical properties (uniaxial compressive strength, pore characteristics and microstructure) of MMS-CBM are significantly affected by fly ash addition and curing temperature. With the increase of fly ash addition, the number of active particles and hydration products involved in the hydration reaction gradually increased, and the physical properties of MMS-CBM were gradually optimized. With the increase of curing temperature, the hydration reaction rate and hydration reaction degree of MMS-CBM gradually deepened, which accelerated the volcanic ash reaction of fly ash particles, which had a promoting effect on the early intensity of MMS-CBM. However, the subsequent strength of MMS-CBM will be affected by thermal damage, resulting in deterioration of physical properties and seriously affecting the long-term stability of MMS-CBM. In addition, the porosity and fractal dimension of MMS-CBM are linearly related to the uniaxial compressive strength, indicating that the pore characteristics can reflect the mechanical properties of MMS-CBM. This study provides a theoretical reference value for the application of MMS-CBM in high-temperature deep wells.

Micro-mechanism on strength development and failure mode of cemented ultra-fine tailing backfill: Influence of binder

As cemented ultra-fine tailings filling method gains popularity, the demands for more economical and environment friendly binders rise. In order to better understand the influence of different binders on the mechanical properties of cemented ultra-fine tailings backfills (CUTBs), the CUTBs with solid materials of 72% for 3, 7, 14, 21 and 28d respectively were made by the water-quenched slag binder (WSB) and ordinary Portland cement (OPC). The microstructure characteristics and macro-mechanical properties of WSB-CUTB and OPC-CUTB at different ages were compared by uniaxial compressive strength (UCS), thermo-gravimetry (TG), X-ray diffraction (XRD) and surface electron microscope (SEM) tests. The results show that the strength development process of CUTBs with different binders has obvious phased characteristics, which can be divided into the initial germination (IG) stage, rapid growth (RG) stage and slow growth (SG) stage: the UCS of WSB-CUTB increases quicker than UCS of OPC-CUTB at the IG and RG stages, while the UCS of OPC-CUTB increases faster than UCS of WSB-CUTB at the SG stage. The micro-mechanism on strength development of CUTBs with different binders was revealed by the evolutional characteristics in the amounts and shapes of hydration products: the amount and shape of AFt are the primary factors which impact the strength development at the IG and RG stages, while the amount and shape of C-S-H are the primary factors which impact the strength development at the SG stage. As the age increases, WSB-CUTB transitions from brittle failure to brittle-ductile failure, while OPC-CUTB transitions from ductile failure to brittle-ductile failure. The micro-mechanism on the failure modes of CUTBs with different binders was revealed by the different characteristics in the skeleton composed of hydration products: the CUTBs with AFt-dominated skeleton will transition from brittle failure to brittle-ductile failure, while the CUTBs with C-S-H-dominated skeleton will transition from ductile failure to brittle-ductile failure. The research results provided theoretical guidance for applying CUTBs using WS as a binder.

Experimental and practical investigation of reinforcement mechanism on permeable polymer in loose area of drainage pipeline

Permeation grouting is one of the important methods of anti-seepage reinforcement when the drainage pipes crosses loose diseases caused by leakage. With the development of grouting materials, permeable polymer slurry is widely used in engineering practice. Due to its low viscosity, fast reaction and micro-expansion, the diffusion and reinforcement law of slurry in loose area of drainage pipeline is more complex. To better understand the effects of water head pressure, grouting pressure, sand particle size and clay content on the anti-seepage and reinforcement effect of permeable polymer grouting in loose area of drainage pipeline, several types of tests, including permeability and uniaxial compressive strength tests, were performed. Then, based on the model test results, a BP neural network prediction model for the anti-seepage reinforcement effect of permeable polymer grouting in loose area of drainage pipeline is constructed, and the research results are applied to the treatment project of loose area of drainage pipeline for verification. The results show that: 1) after grouting, the order of magnitude of permeability coefficient of the consolidated body is reduced to 10-7cm/s, the anti-seepage performance of the sand layer is greatly improved, and the grouting pressure is the main controlling factor affecting the anti-seepage performance of the consolidated body. 2) The compressive strength of the consolidated body is obvious different under different working conditions. The water head pressure is the main controlling factor affecting the strength of the consolidated body. 3) Due to the limitation of test conditions, the relative error between the predicted value of BP neural network model and the actual value is about 20%, which can meet the general prediction needs.

Evaluation of material properties of cultural heritage building by destructive and non- destructive testing: Malatya Taşhoran Church case study

Historical masonry structures are an essential component of cultural heritage. These structures may transfer the lifestyle of previous civilizations to next generations. In order to prevent earthquake damage to these structures, it is important to obtain accurate information on their material properties for reliable computational modelling and strengthening intervention programs. In this context, Destructive Techniques (DT) and Non-Destructive Techniques (NDT) were used together and the results obtained were compared. Taşhoran Church located in Malatya, Turkey was selected as a case study. The aim of this study is to compare the obtained results of Destructive Techniques (DT) and Non-Destructive Techniques (NDT) used to evaluate the original and restoration stones of Taşhoran Church in Malatya, Turkey. The tests conducted include uniaxial compressive strength, flexural strength, water absorption, density, porosity, XRD, SEM-EDX and ageing tests with different solutions (5% H2SO4, 5% HCl and %14 Na2SO4). In addition, NDT methods such as Schmidt hardness, ultrasonic pulse velocity and infrared thermography were used to determine dynamic Poisson's ratio, dynamic modulus of elasticity and UCS. NDT and DT values of the original and restoration stones werepresented.

Fuzzy random evaluation of creep model of frozen soft soil in metro tunnel construction using artificial ground freezing technique

Mastering the creep characteristics of artificial frozen soil and scientifically evaluating the creep model is an important guarantee for the safety of subway tunnel freezing construction. Base on the construction of Nantong metro tunnel, the uniaxial compressive strength tests of the artificially frozen soft soil were carried out to obtain the influence law of temperature on the uniaxial compressive strength, and the uniaxial creep tests were carried out to obtain the influence law of temperature and stress grade on creep, at − 5, − 10 and − 15 °C. The experimental results show that the creep characteristics of frozen soft soil specimens have obvious fuzzy randomness. The traditional ant colony algorithm is improved by optimizing the pheromone fuzzification coefficient, which improves the search efficiency and avoids the local optimum effectively. Subsequently, the improved fuzzy ant colony algorithm is used to invert the flexibility parameters of commonly used permafrost creep models. The fuzzy weight of evaluation index and the fuzzy random evaluation matrix were determined to evaluate the optimal creep model under three different stress levels of frozen soft soil. Finally, the reliability of the fuzzy random evaluation method was verified by engineering measured data.

Analisis Uji Kuat Tekan Uniaksial Batupasir Pada Formasi Pamaluan, Kecamatan Longikis, Kabupaten Paser, Provinsi Kalimantan Timur

The uniaxial compressive strength test was carried out to determine the value of rock strength. This research was conducted on sandstones in the Pamaluan Formation. The tests carried out in this study were physical properties tests, compressive strength tests and grain size tests on sandstones with a total of 30 samples on the physical properties test, 10 samples on the mechanical test and 500 gram grain size test at each point, the purpose of which is to determine the effect of porosity on the compressive strength of rock. In testing the physical properties carried out, the lowest and highest porosity values ​​were 17.27 and 22.91%. The results of the compressive strength test with the lowest and highest values ​​were 3.05 and 7.63 MPa. The grain size test results at points 1 and 2 are the same, namely fine sandstones with a percentage of 45 and 44%. From the results of research that has been done the value of porosity and grain size is very influential on the compressive strength test.

Mechanical properties and disintegration behavior of EICP-reinforced sea sand subjected to drying-wetting cycles

Enzyme-induced carbonate precipitation (EICP) has emerged promising in various geotechnical applications, and has been presented as an alternative to the traditional cementitious materials-based ground improvement method. However, the study on mechanical properties and disintegration behavior of EICP-reinforced sea sand subjected to drying-wetting cycles are limited. This study investigated the mechanical properties and disintegration behavior of EICP-reinforced sea sand against the impact of drying-wetting (D-W) cycles. The uniaxial compressive strength (UCS) tests were performed to discuss the effect of drying-wetting cycles on the mechanical behavior of EICP-treated sea sand. The disintegration tests were conducted on EICP-treated sea sand to investigate the disintegration resistance of bio-cemented samples with various cementation levels. The microstructures of samples before and after disintegration were examined to disclose the disintegration mechanisms of EICP-reinforced sea sand. D-W cycles significantly affect the mechanical properties of EICP-reinforced sea sand, with UCS decreasing by 63.7% after undergoing 15 D-W cycles. The disintegration resistance index of specimens with a lower cementation level decreases significantly under the effect of D-W treatment. The higher disintegration resistance of specimens with higher cementation can be attributed to more crystals with better crystallinity formed in the contact point between sand particles within specimen. The crystals formed by soybean husk urease are mainly calcite and the crystallinity of spherical calcites would gradually change into larger rhombic calcite with further bio-grouting. The crystal with poor crystallinity is susceptible to the effect of D-W treatment, resulting in the obvious disintegration of EICP-reinforced sea sand. Overall, this study is expected to provide useful guidance on the long-term stability and drying-wetting disintegration mechanisms of EICP-reinforced sea sand.

Mechanical and Microstructural Properties of Cemented Paste Backfill with Chloride-Free Antifreeze Additives in Subzero Environments

Cement paste backfill (CPB) is an innovative technology of recycling mine waste (tailings) into construction materials to increase mine safety and productivity and promote sustainable mining. However, the application of CPB technology in mines located in cold or permafrost areas has been difficult due to freezing temperatures. These subzero temperatures can cause fresh CPB to freeze while being transported through the pipelines, which has significant financial implications for the mine. To overcome these problems, antifreeze additives are added to the CPB during its mixing or preparation to enhance the rheological properties of fresh CPB. The addition of antifreeze additives in CPB is an inexpensive and easy-to-operate method currently known to ensure its smooth delivery in subzero environments. But the mechanical and microstructural characteristics of CPB with chloride-free antifreeze additives in subzero conditions are not well understood. Therefore, this study experimentally examined the mechanical (strength, deformation behavior) and microstructural properties of CPB containing chloride-free antifreeze additives and cured under subzero conditions. Three kinds of chloride-free antifreeze (calcium nitrate, calcium nitrite, and urea) with different concentrations (0, 5, 15, and 35 g/L) were separately added to the CPB samples curing at different subzero environments (−1°C, −6°C, and −12°C) for different ages (7, 28, 60, and 90 days). The uniaxial compressive strength (UCS) tests, a series of microstructural (XRD, MIP, DT/DTG, SEM) analyses and monitoring (suction, volumetric water content) experiments of CPB were performed. The obtained results showed that the addition of antifreeze weakened the mechanical properties of CPB. Furthermore, the UCS of CPB was significantly affected by the antifreeze type, antifreeze concentration and subzero curing temperature. The findings in this research will support the successful application of antifreeze cemented backfill technology in cold regions.

Empirical correlation of uniaxial compressive and shear strength of jointed granitic rock

Shear Strength of jointed rock plays a significant role in the stability of rock mass structure especially if the developments plan to be constructed adjacent to this formation. However, to get the shear strength of the rock joints is quite costly and difficult to be identified directly at site. This research is conducted to establish the relationship between uniaxial compressive strength (UCS) and shear strength of jointed granitic rock. UCS parameters are quite easily identified and common practise in any construction project such as deep foundation and tunnelling. The result of uniaxial compressive strength test and direct shear test were plotted using 5 samples of cylindrical shape and 5 jointed rock samples respectively. The linear regression analysis produces meaningful correlation with R2 value of 0.8595 and a new correlation to estimate shear strength of jointed rock has been established.

Effect of dry-wet cycles on mechanical properties of polyurethane porous mixture

ABSTRACT Polyurethane porous mixture (PUPM) is a novel material with potential to extend the service life of pervious pavement. The porous structure makes the interior of the pavement material inevitably exposed to frequent cyclic action of environmental factors. However, the mechanical property decay behaviour of PUPM under the dry-wet cycles formed by water, air and corrosive ions is still unclear. Therefore, the mechanical properties of PUPM under different dry-wet cycles were characterised by Marshall stability, splitting strength and uniaxial compression strength tests. The variations in the microscopic properties of PUPM were investigated by computed tomography (CT), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. The grey entropy correlation theory was used to analyse the effect of variations in the functional groups of polyurethane on the mechanical properties of PUPM. It was concluded that the ageing of the polyurethane and the disruption of the bond at the binder-aggregate interface are the fundamental reasons for the mechanical property decay of PUPM. The influence of each functional group on the mechanical strength of the PUPM is in this descending order: amino groups linked to the carbonyl groups, carbonyl groups, ether bonds, methylene groups, and amino groups formed hydrogen bonds with water.

Influence of Pretreatment Methods on Compressive Performance Improvement and Failure Mechanism Analysis of Recycled Aggregate Concrete.

The utilization of recycled aggregate can avert the squandering of resources and the destruction of the environment. Nevertheless, there exists a slew of old cement mortar and microcracks on the surface of recycled aggregate, which give rise to the poor performance of aggregates in concrete. In this study, for the sake of ameliorating this property of recycled aggregates, the surface of the recycled aggregates is covered with a layer of cement mortar to compensate for the microcracks on the surface and reinforce the bond between old cement mortar and aggregates. In order to demonstrate the influence of recycled aggregate by different cement mortar pretreatment methods, this study prepared natural aggregate concrete (NAC) and concretes with recycled aggregate after the wetting pretreatment (RAC-W) and cement mortar pretreatment (RAC-C), and conducted uniaxial compressive strength tests on different types of concrete at different curing ages. The test results indicated that the compressive strength of RAC-C at a 7 d curing age was higher than that of RAC-W and NAC, and the compressive strength of RAC-C at a 28 d curing age was higher than RAC-W but lower than NAC. The compressive strength of NAC and RAC-W at a 7 d curing age was about 70% of that at a 28 d curing age, and the compressive strength of RAC-C at a 7 d curing age was about 85-90% of that at a 28 d curing age. The compressive strength of RAC-C increased dramatically at the early stage, while the post-strength of the NAC and RAC-W groups increased rapidly. The fracture surface of RAC-W mainly occurred in the transition zone between the recycled aggregates and old cement mortar under the pressure of the uniaxial compressive load. However, the main failure of RAC-C was the crushing destruction of cement mortar. With changes in the amount of cement added beforehand, the proportion of aggregate damage and A-P interface damage of RAC-C also changed accordingly. Therefore, the recycled aggregate pretreated with cement mortar can significantly improve the compressive strength of recycled aggregate concrete. The optimal amount of pre-added cement was 25%, which is recommended for practical engineering.

Experimental Study of Mechanical Properties and Failure Characteristics of Coal-Rock-like Composite Based on 3D Printing Technology.

Coal contains cracks and has strong heterogeneity, so the data dispersion is large in laboratory tests. In this study, 3D printing technology is used to simulate hard rock and coal, and the rock mechanics test method is used to carry out the coal-rock combination experiment. The deformation characteristics and failure modes of the combination are analyzed and compared with the relevant parameters of the single body. The results show that the uniaxial compressive strength of the composite sample is inversely proportional to the thickness of the weak body and directly proportional to the thickness of the strong body. The Protodyakonov model or ASTM model can be used as a verification method for the results of a uniaxial compressive strength test of coal-rock combination. The elastic modulus of the combination is the equivalent elastic modulus, and the elastic modulus of the combination is between the elastic modulus of the two constituent monomers, which can be analyzed using the Reuss model. The failure of the composite sample occurs in the low-strength material, while the high-strength section is rebounding as an extra load on the low-strength body, which may cause a sharp increase in the strain rate of the weak body. The main failure mode of the sample with a small height-diameter ratio is splitting, and the failure mode of the sample with a large height-diameter ratio is shear fracturing. When the height-diameter ratio is not greater than 1, it shows pure splitting, and when the height-diameter ratio is 1~2, it shows a mixed mode of splitting and shear fracture. The shape has a significant effect on the uniaxial compressive strength of the composite specimen. For the impact propensity, it can be determined that the uniaxial compressive strength of the combination is higher than that of the single body, and the dynamic failure time is lower than that of the single body. It can hardly determine the elastic energy and the impact energy of the composite with the relationship to the weak body. The proposed methodology provides new cutting-edge test technologies in the study of coal and coal-like materials, with an exploration of their mechanical properties under compression.

Experimental Investigation on the Influence of Crack Width of Asphalt Concrete on the Repair Effect of Microbially Induced Calcite Precipitation.

The appearance of cracks is one of the reasons that affect the performance of asphalt pavement, and traditional repair methods have the potential problem of causing adverse effects on the environment. In this paper, an environmentally friendly method for asphalt concrete crack repair was investigated using microbially induced calcite precipitation (MICP) for asphalt concrete cracks of different widths (0.5 mm, 1.0 mm, 1.5 mm, and 3 mm), and the effectiveness of repair was evaluated using nondestructive and destructive experiments. A varied ultrasonic pulse velocity was used to evaluate the healing process, and it was found that the samples with an initial crack width of 0.5 mm showed the most significant increase in wave velocity of 18.06% after repair. The results also showed that the uniaxial compressive strength and indirect tensile strength of the MICP-repaired samples recovered up to 47.02% and 34.68%. Static creep test results showed that MICP-repaired samples with smaller width cracks had greater resistance to permanent deformation. The results of uniaxial compressive strength tests on larger width (3 mm) cracks repaired by MICP combined with fibers showed that the strength of the samples was significantly increased by the addition of fibers. In addition, the SEM/EDS results showed that the MICP products were spherical calcite particles with a particle size distribution from 0 to 10 μm. This study shows that MICP has some potential for repairing cracks in asphalt concrete of different widths within the range investigated.

The effect of physical properties of sandstone on the compression strength of rock

Sandstone are commonly found on Lombok Island. The research aims to determine the sandstone’s physical and mechanical properties against the uniaxial compressive strength test. Analysis of physical properties for this research was carried out to determine the dimensions of size, moisture content, specific gravity, and bulk density, while the analysis of mechanical properties was to obtain compressive strength values. The original dry and wet bulk weights were obtained by testing the physical properties and compressive strength of sand and trass. The results from the samples in the Gunung Jae show that the average water content was 8.275%, the specific gravity was 2.37 grams, the bulk density was 0.485 gr/cc, and the compressive strength test was the highest value of 14 mm with the stress of 0.18 MPa.

Lithospheric strength and elastic properties for Mars from InSight geophysical data

Elastic moduli and unconfined compressive strength (UCS), material constants which help constrain the mechanical behaviors of rock materials, are useful for developing accurate models of geologic processes like fracturing and faulting. On Earth, UCS and elastic moduli for intact rock can be measured with uniaxial and triaxial compressive strength tests; however, when geological units are highly fractured, it is more appropriate to estimate these parameters for the rock mass, fractures included. At depth, these estimations can be obtained using seismic wave velocities where stronger more intact rock masses result in faster velocities. We use seismic wave velocities from the InSight Lander to derive the elastic moduli and UCS for the upper crust, lower crust, and mantle of Mars. These estimates could be used in developing models for lithospheric deformation on the red planet.

Electrochemical Accelerating Leaching Behavior of Plastic Concrete for Cut-Off Walls

Plastic concrete is a ductile material with a low elastic modulus (1000–3000 MPa), good flexibility, a and strong ability to adapt to the surrounding soil deformation. Hydraulic concrete mainly serves in a watery environment, so the leaching behavior of plastic concrete is crucial and cannot be neglected. Meanwhile, improving the crack resistance and effect of anti-seepage is also a primary task for cut-off walls. In this paper, in order to investigate the mechanical performance and leaching behavior of plastic concrete, a uniaxial compressive strength test was performed on plastic concrete specimens of a specific age (28 days) and different percentages of replacement cement by single bentonite (40%, 50%, and 60%) and bentonite (30%) together with clay (10%, 20%, and 30%), and the compressive strength, elastic modulus, pH value of the leaching solution, ultrasonic transmit time, electrical resistivity, and calcium ion dissolution concentration of plastic concrete have been evaluated. Moreover, the quantitative relationship between pH value and calcium ion concentration change was built through the electrochemical accelerating leaching method. According to the results, adding 40–60% soil materials can entirely meet the compressive strength (2–7 MPa), elastic modulus (below 3000 MPa), and relative permeability coefficient (below 1 × 10−7 cm/s) of plastic concrete used for cut-off walls while the compressive strength and elastic modulus of plastic concrete with 30% replacement cement by bentonite would be higher than 7 MPa and 3000 MPa, respectively. The leaching resistance of plastic concrete can be improved by more than 30% by adding bentonite coupled with clay, and three representative zones were observed through SEM and energy spectrum analysis, and Ca/Si molar ratio decreased by 30% after leaching.

Thermal effect on the geo-engineering characteristics of a rock salt.

Rock salt caverns are considered one of the best hosts to store oil, natural gas, radioactive and toxic wastes due to their low permeability, self-healing characteristics and wide distribution on the Earth. Stored nuclear waste in rock salts will radiate for many years. Therefore, the thermal energy and also temperature in the host environment will increase depending on time. In this study, P-wave velocity (Vp), Brazilian tensile strength (σt), uniaxial compression strength (σc) of Çankırı rock salt were investigated under different temperatures ranging from 20°C to 250°C since the temperature is a factor that causes changes in some physical and geo-mechanical properties of rocks. The acoustic emission technique was utilized during uniaxial compression strength tests, to monitor the crack accumulation. Additionally, X-ray micro-computed tomography technique was employed to observe the microstructure and determine the porosity of rock salt samples depending on the temperature. The Vp and the σt of Çankırı rock salt decrease with increasing temperatures of samples whereas the σc increases. The ductility of rock salt tends to increase with augmented temperature and the axial strain at the ultimate stress level is 2.96% at 20°C whereas it reaches up to 6.29% at 250°C. The AE activity of rock salt generates at the early stages of loading and AE count prominently increases with the increasing temperature of samples. Therefore, the stress levels of crack initiation (σi) and crack damage (σcd) thresholds were reached earlier than the previous one with each temperature increment. According to X-ray micro-CT images of rock salts, the number of cracks increased markedly in thermally treated rock salt samples and therewith the porosity increases from 1.12% to 2.73% with an increase in temperature from 50°C to 250°C.

Mechanical properties and damage constitutive model of phosphogypsum-based cemented backfill under hydrochemical action

In order to analyze the early mechanical properties and damage characteristics of phosphogypsum-based cemented backfill (PCB) under hydrochemical action, hydrochemical erosion and uniaxial compression strength (UCS) tests were carried out with HCl solution, NaOH solution, and water respectively. The damage degree is defined by taking the effective bearing area of the soluble cements of PCB under hydrochemistry action as the chemical damage variable, and the modified damage parameter α, which reflects the damage development characteristics, is introduced to construct the damage constitutive model of PCB considering chemical damage and load damage, and the theoretical model is verified with the experimental results. The results show that the damage constitutive model curves of PCB under different hydrochemical action are in good agreement with the experimental results, which verifies the correctness of the theoretical model. When the modified damage parameter α decreases from 1.0 to 0.8, the residual load-bearing capacity of PCB gradually increases, with the damage values of PCB samples in HCl solution and water gradually increasing before the peak and decreasing after the peak, while the damage values of PCB samples in NaOH solution show an overall increasing trend before and after the peak. The slope of the post peak curve of PCB decreases with increasing model parameter n. The results of the study can provide theoretical support and practical guidance for the strength design, long-term erosion deformation, and prediction of PCB in hydrochemical environment.