Mechanical Properties Of Limestone Research Articles

Investigations on the effect of natural veined calcite on the mechanical properties of limestone.

The damage behavior of limestone rock masses containing calcite mineral filling under uniaxial compression experimental conditions is unclear, and the fracture mechanism of the rock masses needs to be further explored. In this study, uniaxial compression tests were conducted on limestone rock specimens containing veined calcite by combining acoustic emission and digital image correlation techniques. The effects of veined calcite on the generation and development of cracks on the surface of the specimens until the formation of macroscopic penetration and the strength properties of the rock mass were analyzed. The results showed that the transversely distributed veined calcite caused significant stress concentrations in the rock specimens. The longitudinally distributed veined calcite caused cracks in the specimens or influenced the expansion path of the longitudinal principal cracks. The final damage pattern of the specimens didn't differ significantly from that of conventional rock masses due to the presence of veined calcite. The presence of the veined calcite had effect on the uniaxial compressive capacity of the rock, but the load variation process of the specimen with time still conformed to the load variation pattern during the uniaxial compressive test of conventional rocks.

Effect of Microstructure on Changes to the Pore Structure and Mechanical Properties of Limestone under Acidic Groundwater Corrosion

Effect of Microstructure on Changes to the Pore Structure and Mechanical Properties of Limestone under Acidic Groundwater Corrosion

Effects of heat-treatment on physical and mechanical properties of limestone

The susceptibility of buildings to fire makes it crucial to examine the physical and mechanical (P&M) properties of building stones under high temperature, which is necessary to predict and evaluate the safety and stability of stone structures. In this study, uniaxial compression (UC) and Brazilian splitting (BS) tests were performed on heat-treated limestone specimens and digital image correction (DIC) techniques were utilized to measure specimen deformation. Correlation analysis (CA) and principal component analysis (PCA) were conducted on the mechanical parameters obtained from the UC and BS tests, resulting in the establishment of three principal components (y1c, y2c and y1t) that comprehensively reflect the compressive and tensile properties; these were then utilized to analyze the sensitivity of mechanical properties to temperature changes. Furthermore, based on prior experimental data regarding the fundamental physical parameters of granite, one principal component (y1w) that comprehensively reflects fundamental physical characteristics was established and utilized to predict the uniaxial compression strength (σc) and tensile strength (σt). The results indicate that the compressive properties (σc, Poisson's ratio, elastic modulus and principal compressive strain) and tensile properties (σt and tensile strain) are all affected by temperature changes; as tensile strength is sensitive to temperature changes, special attention should be paid to fire and high temperature of stone buildings with the components subjected to the tensile stress; basic mechanical properties (σc and σt) can be well predicted by a principal component (y1w) which provides a new idea for calculating indirectly the residual mechanical properties of building stones after high temperature or fire.

Influence of the combined action of water and axial pressure on the microscopic damage and mechanical properties of limestone

As one of the main methods, hydraulic fracturing method is widely used in underground energy exploitation. Groundwater not only restricts the energy exploitation efficiency, but seriously affects the safety and stability of underground energy storage structure. To study the influence of groundwater and geostress on hydraulic fracture propagation and rock failure mechanism, the water injection tests were performed on limestone under different constant axial loading (0, 1, 2 and 3 MPa). After water injection, the evolution law of the micropore structure in water-injection samples were studied through SEM and mercury-injection tests; Moreover, the mechanical properties of the water-injection samples were studied through laboratory loading crushing tests. During loading process, the acoustic emission (AE) and infrared radiation temperature (IRT) parameters were collected synchronously and nondestructively. The results indicated that the pore size and porosity of limestone considerably increased with increasing axial pressure, and obvious stage characteristics of the stress-strain curve, cumulative AE energy and IRT difference were determined. Furthermore, the strength, cumulative AE energy and cumulative IRT difference decreased continuously with increasing axial pressure. Compared to limestone subjected to only water injection, the cumulative AE energy of the specimens subjected to high-pressure water under 1–3 MPa axial pressure decreased by 11.31%, 24.71% and 25.56%, and the IRT difference decreased by 10.71%, 19.64% and 26.79%, respectively. In addition, the extreme values of both cumulative AE energy and IRT occurred earlier than the peak stress, which can be interpreted as a sign of structural failure in limestone.

Mechanism Study and Performance Evaluation of Nano-Materials Used to Improve Wellbore Stability

In the drilling process of Tarim Oilfield, a representative of ultra-deep oil and gas reservoirs, there are many problems of wellbore stability/instability caused by the development of a large number of micro-fractures. According to the nano-plugging mechanism, rigid nano-SiO2 and deformable nano-paraffin emulsion are added to the drilling fluid to improve the plugging rate. The effect of nanomaterials on the mechanical properties of limestone in the Karatal Formation was evaluated through a triaxial mechanical experiment, and it was found that rigid nano-SiO2 can have a better plugging effect under high formation pressure. It can increase the compressive strength of the limestone core by 10.32% and the cohesion of the core by 12.19%, and the internal friction angle of the core was increased from 25.67° to 26.39°. The internal structure of the core after nano-blocking was observed using CT scanning, and the fracture distribution state of the core before and after plugging and the fracture characteristics of the core under the pressure gradient were obtained, which confirmed that nano-SiO2 can effectively solve the fracture problem of deep limestone caused by micro-fractures.

Experimental Study on the Effect of Thermal Shock on Physical and Mechanical Properties of Limestone

Thermal shock is the physical process of rapid cooling of a hot object. The physical and mechanical properties of rocks that have undergone thermal shock will change. This variation can be applied to the development of geothermal in limestone reservoirs and serve as an effective means of enhancing heat exchange capacity. The essence of this is rock thermal shock rupture. The reason for the change in rock properties due to thermal shock is distinguished from other factors and is a process of instantaneous impact thermal stress caused by non-constant heat transfer, resulting in rock damage from microscopic damage to macroscopic damage. In order to study the variation of physical and mechanical properties of limestone with heating and cooling temperatures under the effect of thermal shock, a self-developed thermal shock test device was used to test the physical and mechanical properties of limestone heated to 100 °C~600 °C after thermal shock. The results strongly suggest that the heating temperature under the effect of thermal shock is the main factor affecting the evolution of basic physical properties of limestone; with the increase in heating temperature, the color of the specimen changes from off-white to white, the mass decreases and the volume nonlinearly increases, with a maximum reduction of 1.39% in mass and a maximum expansion of 2.79% in volume at 600 °C. Indeed, 500 °C is the temperature of abrupt mass loss. The heating temperature and the cooling medium temperature act together to deteriorate the mechanical properties of limestone. With increasing heating temperature (decreasing cooling temperature), the uniaxial compressive strength of limestone decreased by 39.5% (19.3%), modulus of elasticity by 59.5% (22.9%), tensile strength by 42.9% (7.6%), and cohesion by 43.2% (22.5%). The peak strain increases by 74.2% and the angle of internal friction increases by 27% (25.9%). The above data are average values. The empirical equations of the compressive strength, modulus of elasticity, tensile strength of limestone under the action of thermal shock versus heating temperature were obtained. The differences in the physical and mechanical properties of limestone after two heat treatments (thermal shock and high-temperature heating) were compared and analyzed, and the results showed that the physical and mechanical properties of limestone deteriorated more severely after thermal shock compared to high-temperature heating. The research results can provide technical support for the drilling of geothermal development and wellbore stability assessment in limestone reservoirs, and enrich the theory of high-temperature rock mechanics.

Effect of the Number and Distribution of Circular Holes on the Damage and Fracture of Limestone Using PFC2D

The common occurrence of various number and distribution of hole flaws complicates the mechanical behavior and fracture mode of the rock masses that contain them. This study develops seven numerical models of limestone samples with different numbers and distributions of circular hole flaws using 2-D particle flow discrete element code (PFC2D) to investigate their impact on the mechanical properties of limestone while maintaining the same flaws area. In addition, it analyzes the effect of these factors on the mesomechanical features of each model, including the characteristic stress values (peak stress, crack initiation, and damage stress), crack evolution, stress, and displacement field. The results showed that the peak stress, crack initiation, and damage stress of the single-hole model are between those of multihole models. As the arrangement of dip angle increases, the peak stress, crack initiation, and damage stress of models with the same number of multihole flaws exhibit a V-shaped change. The characteristic stress values are the largest when the holes are vertically aligned. Model differences in crack development path, shape, and number, as well as stress concentration area and failure mode, are primarily due to the number and distribution of holes. The circular holes are arranged at approximately 45°, and the greater the number of defects, the more likely the model is to fail. The study’s findings can provide support and reference for the research system of deformation and failure of rock mass with hole flaws.

Damage mechanism and heat transfer characteristics of limestone after thermal shock cycle treatments based on geothermal development

Since coal and petroleum resources are facing depletion, geothermal resources that can be stably mined for a long time are increasingly valued, especially hot dry rock (HDR). However, thermal shock damage of rock is an unavoidable problem in the development of HDR. The effects of thermal shock fatigue on the physical and mechanical properties and heat conduction of limestone are analyzed in this paper. The limestone is subjected to 1–5 heating and cooling cycles at 100 °C–500 °C. The L* a* b* values, P-wave velocity, thermal conductivity, and tensile strength of the treated limestone are obtained. The experimental results show that the P-wave velocity, thermal conductivity, and tensile strength of limestone decrease with an increase in the temperature for a constant number of thermal cycles. When the temperature is constant, the wave velocity, thermal conductivity, and tensile strength of the limestone decrease with an increase in the number of heating and cooling cycles. In addition, the numerical simulation indicates that the heat treatment temperature, the number of cycles, and the heat transfer time have significant effects on the internal heat transfer of the limestone. Changes in the calcite crystal structure due to fatigue after multiple thermal shocks can lead to cracks between crystals, significantly affecting the physical and mechanical properties of limestone. This study provides insights into the damage characteristics and heat transfer behavior of limestone under thermal shock fatigue, as well as theoretical support for the development of geothermal carbonate reservoirs.

Numerical simulation of the effect of internal hole defect size on the mechanical properties of limestone.

To better understand the effect of the size of hole defects on the mechanical properties of a rock mass, the two-dimensional particle flow discrete element code (PFC2D) is applied to establish rock mass models with single circular hole defects of different diameters. Uniaxial compressive strength (UCS) tests are conducted on each model by only taking the defect size (area) as a variable. This study analyzes each model’s stress-strain, contact force chain, crack evolution, meso-damage and failure, and mechanical properties. The results showed that with the size enlargement of the circular hole defects, each model’s UCS and elastic modulus gradually decrease, and the defect size is negatively correlated with the mechanical strength of the rock samples. The size of the hole defects affects the entire process of contact force chain and crack evolution. The larger the aperture dimension of the circular hole defects in each model, the greater the concentration degree of the contact force chain, the earlier the crack initiation, and the higher the degree of crack coalescence in the post-peak stage. The number of cracks decreases as the hole size increases, and the model is more prone to failure. Rock models’ strength and failure characteristics with different numbers and arrangements of hole defects are discussed under the same defect area condition.

Effect of morphology characteristics on the polishing resistance of coarse aggregates on asphalt pavement

Skid resistance performance of asphalt pavement is an important factor affecting the traffic safety. The long-term skid resistance performance of asphalt pavement depends on abrasion and polish resistance of aggregates. However, the mechanical properties and surface morphological characteristics of aggregates not only affect the road bearing capacity, but also impact the long-term abrasion and polish resistance of asphalt pavement. In this study, the mechanical properties of limestone, basalt, granite and 88 # calcined bauxite were investigated. The macro morphology characteristic parameters (MACP) of coarse aggregates were obtained by Image Pro Plus (IPP) software analysis with strong applicability, and the distribution models and characteristics were further analyzed. In order to present quantitatively the dynamic change process of the macro and micro morphology characteristics of coarse aggregates with the polished stone value (PSV) during the polishing process, a long-term polishing test was carried out on the coarse aggregates. The MACP and micro morphology characteristic parameters (MICP) of coarse aggregates were obtained by the IPP analysis and three-dimensional laser microscope. The grey relation entropy analysis method was used to analyze the correlation degree between morphological characteristic parameters and PSV. The results show that the contents of corundum and mullite in 88 # calcined bauxite are 85.2% and 14.8% severally. Corundum and mullite have the highest Mohs hardness, 9 and 6 respectively. The IPP analysis is suitable for quickly obtaining the MACP of coarse aggregates, and the MACP distribution of four kinds of coarse aggregates satisfies well normal distribution. In addition, in the process of PSV attenuation, the grey entropy correlation coefficients between PSV and fractal dimension, Rq are the highest, 0.9037 and 0.8882 respectively. The fractal dimension of MACP and Rq of MICP are selected as the main various indexes. Meanwhile, the average correlation coefficients of fractal dimension, Rq and PSV are 0.9589 and 0.9809 separately. Therefore, the fractal dimension and Rq are proposed to evaluate the long-term polishing resistance performance of coarse aggregates, and to provide useful references for the long-term skid resistance modeling of durable asphalt pavement.

Elevated Temperature, Freezing–Thawing and Mechanical Properties of Limestone, Marble, and Basalt Powders Reinforced Metakaolin–Red Mud-Based Geopolymer Mortars

Elevated Temperature, Freezing–Thawing and Mechanical Properties of Limestone, Marble, and Basalt Powders Reinforced Metakaolin–Red Mud-Based Geopolymer Mortars

Effect of Freeze-thaw Cycles on Microstructure and Mechanical Properties of Limestone

In studying the effect of freeze-thaw cycles on the microstructure and mechanical properties of limestone, scanning electron microscope, low-field nuclear magnetic resonance, and uniaxial compression tests are carried out on the limestone samples dried and subject to 5, 10, 15, and 20 freeze-thaw cycles. Through analysis and discussion, it was found that the number of freeze-thaw cycles has a significant effect on the microstructure of the limestone samples. Compared to the dry samples, the number of microcracks of the limestone samples subjected to freeze-thaw cycles is increased. Moreover, the crack width is positively correlated to the number of freeze-thaw cycles. With an increase in freeze-thaw cycles, the signal intensity of the T2 spectrum is considerably increased, and the connectivity of the micropores and fissures is increased. In addition, the peak compressive strength and elastic modulus showed a significant negative correlation with the number of freeze-thaw cycles. Again, compared to the dry samples, the peak compressive strength of the samples subject to 5, 10, 15, and 20 freeze-thaw cycles decreased by 14.7%, 22.0%, 28.7%, and 37.5%, respectively. The elastic modulus also decreased by 8.0%, 11.4%, 11.7%, and 21.5%, respectively. Therefore, these findings provide basic parameters for the stability evaluation of rock slopes in Northwest Guizhou.

Mechanical Properties of Limestone After High-Temperature Treatment Under Triaxial Cyclic Loading and Unloading Conditions

Mechanical Properties of Limestone After High-Temperature Treatment Under Triaxial Cyclic Loading and Unloading Conditions

Study on the Influence of Different Aqueous Solutions on the Mechanical Properties and Microstructure of Limestone

Abstract Uniaxial and triaxial compression tests were carried out on limestone samples immersed in distilled water and pH = 2 solution for 80 days to investigate the influences of aqueous solutions on the mechanical properties of limestone. Scanning electron microscopy and image recognition techniques were employed to analyze the morphology of limestone before and after immersion in aqueous solutions. The test results show that the peak stress and elastic modulus of the limestone specimens were reduced while the Poisson’s ratios were increased after 80 days of soaking. A series of chemical reactions take place between water and rock samples during the process of soaking. Energy-dispersive spectrometer analysis results showed that the content of calcium in the surface of the sample decreases after soaking, while the contents of aluminum, magnesium, and silicon are increased. From the image analysis results, it is demonstrated that the number and area of microscopic pores of the sample after immersion increased. The physical-chemical actions between the aqueous solutions and the samples lead to the deterioration of the mechanical properties of the rock.

Research on application feasibility of limestone in sublayer of Double-Layer permeable asphalt pavement

In double-layer permeable pavement, upper layer provides better road performance, and sublayer ensures better lateral drainage capacity. The mechanical properties of limestone are weak, so its application in upper layer is limited, while the sublayer does not directly contact with vehicle load, and the application feasibility of limestone aggregate in sublayer of double-layer permeable asphalt pavement is confirmed in this paper. Optimum asphalt contents and reasonable number of Marshall blows of limestone and basalt PAC-16 (Permeable Asphalt Concrete mixture whose nominal maximum aggregate size is 16 mm) were determined, temperature stability, water stability and water permeability were obtained. Gyratory compaction tests were designed and the compaction characteristics, mechanical properties and aggregate crushing characteristics of limestone and basalt PAC-16 were investigated. Considering the disadvantages of the existing testing methods, the concept of “actual crushing proportion (ACP)” was proposed to calculate the crushing degree of aggregate in mixture under load. It was found that the optimum asphalt content of limestone PAC-16 was higher than that of basalt mixture, and the laboratory properties related to field performance of limestone PAC-16 met the requirements of specifications in general. The equivalent compacting times of limestone mixture are slightly less than that of basalt in order to achieve the same void ratio, and the void ratio decay rate of limestone mixture is much faster than that of basalt mixture after opening to traffic. The ACP results showed that limestone aggregate > 13.2 mm can be replaced by basalt aggregate to ensure the strength of aggregate skeleton.

The mechanical properties of limestone as an aggregate on high strength concrete

The construction of multi-stories buildings is increasing rapidly. In concrete construction, various studies and innovations have been carried out in order to obtain high strength concrete. The use of limestone either as a substitute for fine aggregate, as a substitute for coarse aggregate or as a substitute for fine aggregate and even coarse aggregate in a concrete mixture is still lacking. In South Sulawesi, large quantities of limestone are found in several regencies. Enrekang Regency is one with considerable limestone potential which is about 74.75 km2 or an estimated geological of 3.7 billion cubic meters. Most limestone is made into split stones that can be used as construction materials. Limestone can be processed into split or powder which can be used as a replacement for sand in concrete mixture. The results of the concrete at 28 days with a mixture of natural sand as fine aggregate and limestone split as coarse aggregate, w/c ratio of 0.20 produced a value of f’c = 59.26 MPa. ft = 4.51 MPa (0.61 √f’c), and fr = 7.18 MPa (0.93 √f’c). The average modulus of elasticity at 28 days with a mixture of limestone powder as fine aggregate and limestone split as coarse aggregate produced a value of Ec = 46960.25 MPa (6325 √f’c) with Poisson’s ratio υ = 0.3847.

Correlating Natural, Dry, and Saturated Ultrasonic Pulse Velocities with the Mechanical Properties of Rock for Various Sample Diameters

P-wave velocity is employed in various fields of engineering to estimate the mechanical properties of rock, as its measurement is reliable, convenient, rapid, nondestructive, and economical. The present study aimed to (i) correlate natural, dry, and saturated P-wave velocities with the mechanical properties of limestone and (ii) investigate how the ultrasonic P-wave velocities and mechanical properties of limestone are affected by the sample diameter. This study reveals that P-wave velocities under different environmental conditions can be correlated with the mechanical properties of limestone. Further, the R-value variations with different P-wave velocities for a given sample diameter are (i) negligible in terms of the uniaxial compressive strength (UCS) excluding 63.2 mm, (ii) limited for the diametrical point load index (PLID) except for 53.9 mm, (iii) perceived in case of the axial point load index (PLIA) for 47.7 mm, (iv) observed for the indirect tensile strength (ITS), but generally insignificant, and (v) detected in terms of Schmidt hammer value (SHV) except for 47.7 mm.

Microfracture development and chemical damage analysis of limestone based on fractal theory

To explore the influence of microfracture development caused by chemical dissolution on the mechanical properties of limestone, this paper presents a new numerical simulation and quantitative analysis method. First, the dissolution rate was determined by the theory of chemical kinetics, and a differential equation that can be solved for results of the fracture evolution process by COMSOL Multiphysics was established to describe the microfracture's expansion. The fractal dimensions of the microfractures were found to have a linear relationship with the damage variables at different time periods through analysis of the simulation results with the fractal geometry method using fracture width as the index, which proves that the evolution of damage has a fractal nature. After that, a damage evolution equation was fitted to predict the deterioration in rock mechanical properties under hydrochemical actions and the predictive uniaxial compressive strength of limestone is seen to be in agreement with experimental test results. The application of the fractal geometry method has important engineering significance as it relates the development of microscopic fractures to changes in the macroscopic mechanical properties and predicts the mechanical properties of the rock under chemical damage.

Mechanical properties of limestone from Maixi tunnel under hydro-mechanical coupling

The hydro-mechanical coupling often leads to both mechanical properties and stability deterioration during excavation of water-rich tunnel rock mass. Deformation and mechanical, fracture, and strain energy characteristics of limestone from Maixi tunnel in Guiyang (China) are investigated by hydro-mechanical coupling tests in this paper. Results show that the water pressure has a significant influence on the stress-strain curve, strength characteristics, and macro-fracture degree. The compaction stage is relatively prolonged and elastic phase is shortened. With increasing water pressure, average peak strength decreases exponentially and both average elastic modulus and deformation modulus decrease linearly. The larger the water pressure, the better the fragment uniformity, and fragment uniformity increases exponentially but decreases logarithmically with peak strength. Mercury-injection curve shows a rapid increase then develops gently; the pore volume per unit mass increases exponentially revealing that water pressure has a significant effect on the dissolution pores. Strain energy dissipation characteristics show that total strain energy, dissipation strain energy, and releasable strain energy decrease exponentially with increasing water pressure. Energy ratio Ud/Ut experiences a slow increase, then dramatic rise, and finally develops gently, but Ue/Ut goes through a negative development tend and its boundary points of water pressure are both 2 MPa and 4 MPa. Ud/Ut has a typical logistic function with water pressure reflecting the damage degree and sensitivity of dissipation strain energy to water pressure.

Changes in physical and mechanical properties of limestone and marble after exposure to different high temperatures

Under or after high-temperature treatment, the physical and mechanical characteristics of limestone and marble change significantly. This study seeks to understand the effect of high temperatures on physical and mechanical properties (such as density, porosity, permeability, P-wave velocity, thermal diffusivity, elastic modulus, uniaxial compressive strength, peak strain and Poisson's ratio) of limestone and marble. The results indicate that, from room temperature to 300°C, most of the physical and mechanical indices of limestone and marble change relatively little, except for thermal diffusivity. Above 300°C (especially at 400–600°C), physical and mechanical characteristics change significantly, corresponding to the changes to minerals between 400 and 600°C. These results confirm the important link between physical and mechanical properties and heating temperature, and can provide the basis of theory and reference for related engineering.