Freeze-thaw is one of the most powerful weathering agents that may cause a rapid change in the me... more Freeze-thaw is one of the most powerful weathering agents that may cause a rapid change in the mechanical properties of stones, and thus limit their durability. Consequently, determining the mechanical properties of stones after freeze-thaw is important to select the natural building stones for outdoor applications, which are exposed excessive freeze-thaw cycles. The purpose of this study is propose statistical models for predicting the mechanical properties of travertine building stones after freeze-thaw test. For this, 12 travertine samples were selected and their physical and mechanical properties including density (ρ), water absorption (Wa), uniaxial compressive strength (UCS), and P-wave velocity (V P) were determined. Then, freeze-thaw test up to 60 cycles was carried out and mechanical properties including the UCS and V P of the samples were measured. Using data analysis, statistical models for predicting the mechanical properties of deteriorated samples after freeze-thaw test were proposed. In these models, the mechanical property of samples after freeze-thaw was considered to be the dependent variable-dependent on the independent variables of the initial mechanical property of the samples and their water absorption. The results show that statistical models are in good accuracy for predicting the mechanical properties of samples, and thus a rapid durability assessment.
The quantification of total and effective porosities in travertines using PIA and saturation-buoyancy methods and the implication for strength and durability
Bulletin of Engineering Geology and the Environment, Jun 9, 2017
The porosity of travertine controls its strength characters and durability. In this study, seven ... more The porosity of travertine controls its strength characters and durability. In this study, seven travertine samples were collected from mines in Iran. The saturation-buoyancy (SB) method was used to determine density, water absorption by weight, effective porosity, and total porosity. Petrographic image analysis (PIA) was applied to measure total porosity. Uniaxial compressive strength (UCS) of travertine samples was obtained under both oven-dried and saturated conditions. The results showed that mean PIA total porosity of samples is 2–4 times more than total porosity obtained from the SB method. The underestimation of total porosity by SB method was attributed to pores type and pores size. According to regression analyses, the UCS shows a better correlation with SB effective porosity than SB total porosity. Based on results, water absorption by weight has a large impact on UCS of travertines. The SB effective porosity shows high correlation with water absorption by weight. There is a good power relation between PIA total porosity and UCS of travertines.
Bulletin of Engineering Geology and the Environment, Mar 7, 2018
Durability is the most important characteristic of stones in sustainable architecture. Salt cryst... more Durability is the most important characteristic of stones in sustainable architecture. Salt crystallization has been known to damage porous building stones. Gerdoi and red travertines are extensively used in new buildings in East Azerbaijan province. To this end, petrographic and physical properties, dry and saturated P-wave velocity, uniaxial compressive strength and Brazilian tensile strength were obtained for each freshly quarried stone in the laboratory. The samples were subjected to an aging test in order to examine their resistance against sodium chloride crystallization. Water saturated-to-dry strength ratio (a crude immediate estimator) and a decay function model were applied to assess durability of stones. Gerdoi travertine consists of alternation of densely packed layers (laminated fabric) while red travertine exhibits massive fabric. Albeit Gerdoi travertine has laminated fabric, it shows higher initial strength, P-wave velocity and lower effective porosity and water absorption than Gerdoi travertine. The results showed that a crude immediate estimator is not a sensitive indicator for estimating durability of travertine stones. P-wave velocity, uniaxial compressive strength and Brazilian tensile strength decreased with increasing number of salt cycles. A decay function model confirmed that the integrity loss was higher in red travertine in comparison with Gerdoi travertine. It was found that the integrity loss of both stones based on Brazilian tensile strength is highest than those based on uniaxial compressive strength and P-wave velocity.
Crack evolution in a rock depends on the mineralogy, microstructure and fabric of specific rock t... more Crack evolution in a rock depends on the mineralogy, microstructure and fabric of specific rock type. This study aims to investigate how mineralogy and grain shape affect the microcrack initiation and propagation of granite rock, which contains plagioclase, quartz, k-feldspar, biotite and amphibole, during uniaxial compression loading. Physico-mechanical properties and microcrack features such as linear microcrack density (LMD) and microcrack type were investigated. By acoustic emission (AE) measurements, damage stress thresholds were identified. Then, crack characteristics of a fresh sample were compared with the samples that were loaded until damage threshold stresses. The results demonstrate that at an early stage of loading, pre-existing microcracks growth and LMD of intergranular crack increase. In the elastic phase, all microcracks types increase at the same rate. When the loading reaches to the strength limit of the sample, the total LMD reduced, because cracks start to coalesce and form new and large transgranular microcrack. Investigating crack propagation in mineral shows that at first, microcrack generates in biotite and at last in quartz. Plagioclase has the highest LMD and microcracks usually formed within the cleavage plane, but alteration and inclusions of tiny minerals can drastically change the LMD and orientation of microcracks. Biotite can terminate or let the microcrack to pass through the crystal based on the orientation of the microcrack plane and cleavage microcrack within the mineral. Furthermore, crystals with an aspect ratio higher than two have higher LMD. By getting close to the uniaxial compression strength, more microcracks appear close to the grain boundary which increases the circularity of the grain.
Geotechnical and Geological Engineering, Nov 10, 2016
In order to assess the resistance of travertine against salt crystallization, 15 travertine sampl... more In order to assess the resistance of travertine against salt crystallization, 15 travertine samples were selected from Iran's mines. Petrographic, physical and mechanical properties of the travertine samples were determined, and then salt crystallization test was carried out by using magnesium sulfate (MgSO 4) solution up to 60 cycles. Dry weight increment, dry weight loss, Brazilian tensile strength (BTS), point load strength index and P-wave velocity were calculated at 10, 20, 30, 40, 50 and 60 number of cycles. Two weathering forms (granular disintegration, and alveolaring) were observed in the samples as a result of salt crystallization pressure. Onyx travertine samples were more resistant than travertine samples. It was found out that the deterioration rate at elementary cycles was lower. The results showed that durability of samples has a positive relationship with initial BTS and a negative relationship with initial effective porosity. It was concluded non-destructive tests are good technique for assessment of travertine deterioration in salt crystallization test.
Evaluation of travertine samples deterioration against salt crystallization using alteration index and alteration velocity parameters
Scientific Quarterly Journal of Iranian Association of Engineering Geology, Aug 23, 2013
Salt crystallization is one of the important factors on durability and deterioration of building ... more Salt crystallization is one of the important factors on durability and deterioration of building stones. Magnesium sulphate is a common salt that can lead to deterioration, thus it is necessary to consider this subject before select the stones as building facade. In this research, alteration index and alteration velocity were be used to evaluate the durability of travertine against Magnesium sulphate that can be used as criterion in salt crystallization test. For this purpose, fifteen travertine were sampled from different areas in Iran then petrologic, some chemical (density, porosity and water adsorption) and mechanical properties (uniaxial compressive strength and tensile strength) were obtained for samples. Salt crystallization test were carried out 60 cycles and alteration index, alteration velocity were calculated for samples based on the weight loss and appearance variation of samples then relationship between alteration index and alteration velocity with effective porosity, tensile strength and weight was analyzed with regression analysis. The results show that alteration velocity has higher correlation with tensile strength, effective porosity and weight loss whereas the alteration index of the travertine is not. Also the results show that fabric, effective porosity and tensile strength are important factors that controll durability of samples in salt crystallization test.
Engineering Geology for Society and Territory - Volume 8, 2014
Freeze-thaw is one of the most powerful weathering agents that may cause a rapid change in the me... more Freeze-thaw is one of the most powerful weathering agents that may cause a rapid change in the mechanical properties of stones, and thus limit their durability. Consequently, determining the mechanical properties of stones after freeze-thaw is important to select the natural building stones for outdoor applications, which are exposed excessive freeze-thaw cycles. The purpose of this study is propose statistical models for predicting the mechanical properties of travertine building stones after freeze-thaw test. For this, 12 travertine samples were selected and their physical and mechanical properties including density (ρ), water absorption (Wa), uniaxial compressive strength (UCS), and P-wave velocity (V P) were determined. Then, freeze-thaw test up to 60 cycles was carried out and mechanical properties including the UCS and V P of the samples were measured. Using data analysis, statistical models for predicting the mechanical properties of deteriorated samples after freeze-thaw test were proposed. In these models, the mechanical property of samples after freeze-thaw was considered to be the dependent variable-dependent on the independent variables of the initial mechanical property of the samples and their water absorption. The results show that statistical models are in good accuracy for predicting the mechanical properties of samples, and thus a rapid durability assessment.
journal of sciences islamic republic of iran, 2017
Salt crystallization is one of the most powerful weathering agents that may cause a rapid change ... more Salt crystallization is one of the most powerful weathering agents that may cause a rapid change in the mechanical properties of stones, and thus limit their durability. Consequently, determining the mechanical properties of stones due to salt crystallization is important for natural building stones used in marine environmental and mild climatic conditions, which expose excessive salt crystallization cycles. In this study, multivariate regression analysis was performed for estimating the mechanical properties of travertine building stones after salt crystallization test. For this purpose, 12 travertine samples were selected and their physical and mechanical properties (density, porosity, uniaxial compressive strength, Brazilian tensile strength, and P-wave velocity) were determined. Then salt crystallization test was carried out at sodium sulfate solution (Na2SO4) up to 50 cycles and, after every 5 cycles, the uniaxial compressive strength, Brazilian tensile strength and P-wave velo...
Evaluation of travertine samples deterioration against salt crystallization using alteration index and alteration velocity parameters
Salt crystallization is one of the important factors on durability and deterioration of building ... more Salt crystallization is one of the important factors on durability and deterioration of building stones. Magnesium sulphate is a common salt that can lead to deterioration, thus it is necessary to consider this subject before select the stones as building facade. In this research, alteration index and alteration velocity were be used to evaluate the durability of travertine against Magnesium sulphate that can be used as criterion in salt crystallization test. For this purpose, fifteen travertine were sampled from different areas in Iran then petrologic, some chemical (density, porosity and water adsorption) and mechanical properties (uniaxial compressive strength and tensile strength) were obtained for samples. Salt crystallization test were carried out 60 cycles and alteration index, alteration velocity were calculated for samples based on the weight loss and appearance variation of samples then relationship between alteration index and alteration velocity with effective porosity, ...
Microcracking Behavior of Gabbro During Monotonic and Cyclic Loading
Rock Mechanics and Rock Engineering, 2021
Microcracks are an integral part of intact rocks that can develop when the rock is exposed to sta... more Microcracks are an integral part of intact rocks that can develop when the rock is exposed to static or dynamic loads. The loading may not fail the rock. It, however, may cause permanent damage to the sample by expanding the existing microcracks or developing new microcracks. Investigating the development of microcracks in intact rocks is significant to investigate the damage evolution, which is not visible in macro-scale. In this study, the evolution of microcracks in gabbro is investigated under static and dynamic loading. Gabbro samples were subjected to monotonic and cyclic loading until a crack stress threshold (i.e., crack closure, crack initiation, crack damage). After each test, microcracking properties of the sample such as Linear Microcrack Density (LMD), crack length and crack types were defined using fluorescence thin section and combining polarized and fluorescence light optical microscopy. The results demonstrated that samples that are subjected to cyclic loading exper...
Artificial microcracking of granites subjected to salt crystallization aging test
Bulletin of Engineering Geology and the Environment
Salt crystallization-induced decay of Vardavard granodiorite and Shirkouh monzogranite, two Irani... more Salt crystallization-induced decay of Vardavard granodiorite and Shirkouh monzogranite, two Iranian building stones, were assessed with two non-destructive methods: saturation-buoyancy technique and P- and S-wave velocity measurement. Moreover, polarized and fluorescence microscopy studies were used to evaluate the behavior of the studied stones at microscopic scale against a salt crystallization aging test. The aging test extended pre-existing microcracks and generated new ones. Intracrystalline microcracking was the most predominant microcrack type for both samples. Fine-grained Vardavard granodiorite experienced higher intercrystalline microcracking than coarse-grained Shirkouh monzogranite. The microcracking mechanism of feldspars substantially depends on their alteration degree and microstructural precursors. When a growing microcrack reaches a biotite, it propagates within the crystal if the growing microcrack coincides with the cleavage plane; otherwise, it propagates as an intercrystalline one. The increase in maximum microcrack length of the samples was higher than the increase in their mean microcrack length. Low-strength Vardavard granodiorite showed higher microcrack width after the aging test. Dry weight loss in low-strength Vardavard granodiorite was more pronounced than in high-strength Shirkouh monzogranite. Dry unit weight decreased at a higher rate than saturated unit weight with the increase of effective porosity. The reduction in ultrasonic wave velocities and the increment in effective porosity and water absorption were more pronounced for Vardavard granodiorite, indicating a higher degree of decay, i.e., higher microcrack generation, enlargement, and widening. Shirkouh monzogranite, which has large-sized crystals and pores, wider initial microcracks, high tensile strength, and low effective porosity and microcrack density, was more durable than Vardavard granodiorite.
Crack Evolution in Damage Stress Thresholds in Different Minerals of Granite Rock
Rock Mechanics and Rock Engineering
Crack evolution in a rock depends on the mineralogy, microstructure and fabric of specific rock t... more Crack evolution in a rock depends on the mineralogy, microstructure and fabric of specific rock type. This study aims to investigate how mineralogy and grain shape affect the microcrack initiation and propagation of granite rock, which contains plagioclase, quartz, k-feldspar, biotite and amphibole, during uniaxial compression loading. Physico-mechanical properties and microcrack features such as linear microcrack density (LMD) and microcrack type were investigated. By acoustic emission (AE) measurements, damage stress thresholds were identified. Then, crack characteristics of a fresh sample were compared with the samples that were loaded until damage threshold stresses. The results demonstrate that at an early stage of loading, pre-existing microcracks growth and LMD of intergranular crack increase. In the elastic phase, all microcracks types increase at the same rate. When the loading reaches to the strength limit of the sample, the total LMD reduced, because cracks start to coalesce and form new and large transgranular microcrack. Investigating crack propagation in mineral shows that at first, microcrack generates in biotite and at last in quartz. Plagioclase has the highest LMD and microcracks usually formed within the cleavage plane, but alteration and inclusions of tiny minerals can drastically change the LMD and orientation of microcracks. Biotite can terminate or let the microcrack to pass through the crystal based on the orientation of the microcrack plane and cleavage microcrack within the mineral. Furthermore, crystals with an aspect ratio higher than two have higher LMD. By getting close to the uniaxial compression strength, more microcracks appear close to the grain boundary which increases the circularity of the grain.
Freeze-thaw is one of the most powerful weathering agents that may cause a rapid change in the me... more Freeze-thaw is one of the most powerful weathering agents that may cause a rapid change in the mechanical properties of stones, and thus limit their durability. Consequently, determining the mechanical properties of stones after freeze-thaw is important to select the natural building stones for outdoor applications, which are exposed excessive freeze-thaw cycles. The purpose of this study is propose statistical models for predicting the mechanical properties of travertine building stones after freeze-thaw test. For this, 12 travertine samples were selected and their physical and mechanical properties including density (ρ), water absorption (Wa), uniaxial compressive strength (UCS), and P-wave velocity (V P) were determined. Then, freeze-thaw test up to 60 cycles was carried out and mechanical properties including the UCS and V P of the samples were measured. Using data analysis, statistical models for predicting the mechanical properties of deteriorated samples after freeze-thaw test were proposed. In these models, the mechanical property of samples after freeze-thaw was considered to be the dependent variable-dependent on the independent variables of the initial mechanical property of the samples and their water absorption. The results show that statistical models are in good accuracy for predicting the mechanical properties of samples, and thus a rapid durability assessment.
The quantification of total and effective porosities in travertines using PIA and saturation-buoyancy methods and the implication for strength and durability
Bulletin of Engineering Geology and the Environment, Jun 9, 2017
The porosity of travertine controls its strength characters and durability. In this study, seven ... more The porosity of travertine controls its strength characters and durability. In this study, seven travertine samples were collected from mines in Iran. The saturation-buoyancy (SB) method was used to determine density, water absorption by weight, effective porosity, and total porosity. Petrographic image analysis (PIA) was applied to measure total porosity. Uniaxial compressive strength (UCS) of travertine samples was obtained under both oven-dried and saturated conditions. The results showed that mean PIA total porosity of samples is 2–4 times more than total porosity obtained from the SB method. The underestimation of total porosity by SB method was attributed to pores type and pores size. According to regression analyses, the UCS shows a better correlation with SB effective porosity than SB total porosity. Based on results, water absorption by weight has a large impact on UCS of travertines. The SB effective porosity shows high correlation with water absorption by weight. There is a good power relation between PIA total porosity and UCS of travertines.
Bulletin of Engineering Geology and the Environment, Mar 7, 2018
Durability is the most important characteristic of stones in sustainable architecture. Salt cryst... more Durability is the most important characteristic of stones in sustainable architecture. Salt crystallization has been known to damage porous building stones. Gerdoi and red travertines are extensively used in new buildings in East Azerbaijan province. To this end, petrographic and physical properties, dry and saturated P-wave velocity, uniaxial compressive strength and Brazilian tensile strength were obtained for each freshly quarried stone in the laboratory. The samples were subjected to an aging test in order to examine their resistance against sodium chloride crystallization. Water saturated-to-dry strength ratio (a crude immediate estimator) and a decay function model were applied to assess durability of stones. Gerdoi travertine consists of alternation of densely packed layers (laminated fabric) while red travertine exhibits massive fabric. Albeit Gerdoi travertine has laminated fabric, it shows higher initial strength, P-wave velocity and lower effective porosity and water absorption than Gerdoi travertine. The results showed that a crude immediate estimator is not a sensitive indicator for estimating durability of travertine stones. P-wave velocity, uniaxial compressive strength and Brazilian tensile strength decreased with increasing number of salt cycles. A decay function model confirmed that the integrity loss was higher in red travertine in comparison with Gerdoi travertine. It was found that the integrity loss of both stones based on Brazilian tensile strength is highest than those based on uniaxial compressive strength and P-wave velocity.
Crack evolution in a rock depends on the mineralogy, microstructure and fabric of specific rock t... more Crack evolution in a rock depends on the mineralogy, microstructure and fabric of specific rock type. This study aims to investigate how mineralogy and grain shape affect the microcrack initiation and propagation of granite rock, which contains plagioclase, quartz, k-feldspar, biotite and amphibole, during uniaxial compression loading. Physico-mechanical properties and microcrack features such as linear microcrack density (LMD) and microcrack type were investigated. By acoustic emission (AE) measurements, damage stress thresholds were identified. Then, crack characteristics of a fresh sample were compared with the samples that were loaded until damage threshold stresses. The results demonstrate that at an early stage of loading, pre-existing microcracks growth and LMD of intergranular crack increase. In the elastic phase, all microcracks types increase at the same rate. When the loading reaches to the strength limit of the sample, the total LMD reduced, because cracks start to coalesce and form new and large transgranular microcrack. Investigating crack propagation in mineral shows that at first, microcrack generates in biotite and at last in quartz. Plagioclase has the highest LMD and microcracks usually formed within the cleavage plane, but alteration and inclusions of tiny minerals can drastically change the LMD and orientation of microcracks. Biotite can terminate or let the microcrack to pass through the crystal based on the orientation of the microcrack plane and cleavage microcrack within the mineral. Furthermore, crystals with an aspect ratio higher than two have higher LMD. By getting close to the uniaxial compression strength, more microcracks appear close to the grain boundary which increases the circularity of the grain.
Geotechnical and Geological Engineering, Nov 10, 2016
In order to assess the resistance of travertine against salt crystallization, 15 travertine sampl... more In order to assess the resistance of travertine against salt crystallization, 15 travertine samples were selected from Iran's mines. Petrographic, physical and mechanical properties of the travertine samples were determined, and then salt crystallization test was carried out by using magnesium sulfate (MgSO 4) solution up to 60 cycles. Dry weight increment, dry weight loss, Brazilian tensile strength (BTS), point load strength index and P-wave velocity were calculated at 10, 20, 30, 40, 50 and 60 number of cycles. Two weathering forms (granular disintegration, and alveolaring) were observed in the samples as a result of salt crystallization pressure. Onyx travertine samples were more resistant than travertine samples. It was found out that the deterioration rate at elementary cycles was lower. The results showed that durability of samples has a positive relationship with initial BTS and a negative relationship with initial effective porosity. It was concluded non-destructive tests are good technique for assessment of travertine deterioration in salt crystallization test.
Evaluation of travertine samples deterioration against salt crystallization using alteration index and alteration velocity parameters
Scientific Quarterly Journal of Iranian Association of Engineering Geology, Aug 23, 2013
Salt crystallization is one of the important factors on durability and deterioration of building ... more Salt crystallization is one of the important factors on durability and deterioration of building stones. Magnesium sulphate is a common salt that can lead to deterioration, thus it is necessary to consider this subject before select the stones as building facade. In this research, alteration index and alteration velocity were be used to evaluate the durability of travertine against Magnesium sulphate that can be used as criterion in salt crystallization test. For this purpose, fifteen travertine were sampled from different areas in Iran then petrologic, some chemical (density, porosity and water adsorption) and mechanical properties (uniaxial compressive strength and tensile strength) were obtained for samples. Salt crystallization test were carried out 60 cycles and alteration index, alteration velocity were calculated for samples based on the weight loss and appearance variation of samples then relationship between alteration index and alteration velocity with effective porosity, tensile strength and weight was analyzed with regression analysis. The results show that alteration velocity has higher correlation with tensile strength, effective porosity and weight loss whereas the alteration index of the travertine is not. Also the results show that fabric, effective porosity and tensile strength are important factors that controll durability of samples in salt crystallization test.
Engineering Geology for Society and Territory - Volume 8, 2014
Freeze-thaw is one of the most powerful weathering agents that may cause a rapid change in the me... more Freeze-thaw is one of the most powerful weathering agents that may cause a rapid change in the mechanical properties of stones, and thus limit their durability. Consequently, determining the mechanical properties of stones after freeze-thaw is important to select the natural building stones for outdoor applications, which are exposed excessive freeze-thaw cycles. The purpose of this study is propose statistical models for predicting the mechanical properties of travertine building stones after freeze-thaw test. For this, 12 travertine samples were selected and their physical and mechanical properties including density (ρ), water absorption (Wa), uniaxial compressive strength (UCS), and P-wave velocity (V P) were determined. Then, freeze-thaw test up to 60 cycles was carried out and mechanical properties including the UCS and V P of the samples were measured. Using data analysis, statistical models for predicting the mechanical properties of deteriorated samples after freeze-thaw test were proposed. In these models, the mechanical property of samples after freeze-thaw was considered to be the dependent variable-dependent on the independent variables of the initial mechanical property of the samples and their water absorption. The results show that statistical models are in good accuracy for predicting the mechanical properties of samples, and thus a rapid durability assessment.
journal of sciences islamic republic of iran, 2017
Salt crystallization is one of the most powerful weathering agents that may cause a rapid change ... more Salt crystallization is one of the most powerful weathering agents that may cause a rapid change in the mechanical properties of stones, and thus limit their durability. Consequently, determining the mechanical properties of stones due to salt crystallization is important for natural building stones used in marine environmental and mild climatic conditions, which expose excessive salt crystallization cycles. In this study, multivariate regression analysis was performed for estimating the mechanical properties of travertine building stones after salt crystallization test. For this purpose, 12 travertine samples were selected and their physical and mechanical properties (density, porosity, uniaxial compressive strength, Brazilian tensile strength, and P-wave velocity) were determined. Then salt crystallization test was carried out at sodium sulfate solution (Na2SO4) up to 50 cycles and, after every 5 cycles, the uniaxial compressive strength, Brazilian tensile strength and P-wave velo...
Evaluation of travertine samples deterioration against salt crystallization using alteration index and alteration velocity parameters
Salt crystallization is one of the important factors on durability and deterioration of building ... more Salt crystallization is one of the important factors on durability and deterioration of building stones. Magnesium sulphate is a common salt that can lead to deterioration, thus it is necessary to consider this subject before select the stones as building facade. In this research, alteration index and alteration velocity were be used to evaluate the durability of travertine against Magnesium sulphate that can be used as criterion in salt crystallization test. For this purpose, fifteen travertine were sampled from different areas in Iran then petrologic, some chemical (density, porosity and water adsorption) and mechanical properties (uniaxial compressive strength and tensile strength) were obtained for samples. Salt crystallization test were carried out 60 cycles and alteration index, alteration velocity were calculated for samples based on the weight loss and appearance variation of samples then relationship between alteration index and alteration velocity with effective porosity, ...
Microcracking Behavior of Gabbro During Monotonic and Cyclic Loading
Rock Mechanics and Rock Engineering, 2021
Microcracks are an integral part of intact rocks that can develop when the rock is exposed to sta... more Microcracks are an integral part of intact rocks that can develop when the rock is exposed to static or dynamic loads. The loading may not fail the rock. It, however, may cause permanent damage to the sample by expanding the existing microcracks or developing new microcracks. Investigating the development of microcracks in intact rocks is significant to investigate the damage evolution, which is not visible in macro-scale. In this study, the evolution of microcracks in gabbro is investigated under static and dynamic loading. Gabbro samples were subjected to monotonic and cyclic loading until a crack stress threshold (i.e., crack closure, crack initiation, crack damage). After each test, microcracking properties of the sample such as Linear Microcrack Density (LMD), crack length and crack types were defined using fluorescence thin section and combining polarized and fluorescence light optical microscopy. The results demonstrated that samples that are subjected to cyclic loading exper...
Artificial microcracking of granites subjected to salt crystallization aging test
Bulletin of Engineering Geology and the Environment
Salt crystallization-induced decay of Vardavard granodiorite and Shirkouh monzogranite, two Irani... more Salt crystallization-induced decay of Vardavard granodiorite and Shirkouh monzogranite, two Iranian building stones, were assessed with two non-destructive methods: saturation-buoyancy technique and P- and S-wave velocity measurement. Moreover, polarized and fluorescence microscopy studies were used to evaluate the behavior of the studied stones at microscopic scale against a salt crystallization aging test. The aging test extended pre-existing microcracks and generated new ones. Intracrystalline microcracking was the most predominant microcrack type for both samples. Fine-grained Vardavard granodiorite experienced higher intercrystalline microcracking than coarse-grained Shirkouh monzogranite. The microcracking mechanism of feldspars substantially depends on their alteration degree and microstructural precursors. When a growing microcrack reaches a biotite, it propagates within the crystal if the growing microcrack coincides with the cleavage plane; otherwise, it propagates as an intercrystalline one. The increase in maximum microcrack length of the samples was higher than the increase in their mean microcrack length. Low-strength Vardavard granodiorite showed higher microcrack width after the aging test. Dry weight loss in low-strength Vardavard granodiorite was more pronounced than in high-strength Shirkouh monzogranite. Dry unit weight decreased at a higher rate than saturated unit weight with the increase of effective porosity. The reduction in ultrasonic wave velocities and the increment in effective porosity and water absorption were more pronounced for Vardavard granodiorite, indicating a higher degree of decay, i.e., higher microcrack generation, enlargement, and widening. Shirkouh monzogranite, which has large-sized crystals and pores, wider initial microcracks, high tensile strength, and low effective porosity and microcrack density, was more durable than Vardavard granodiorite.
Crack Evolution in Damage Stress Thresholds in Different Minerals of Granite Rock
Rock Mechanics and Rock Engineering
Crack evolution in a rock depends on the mineralogy, microstructure and fabric of specific rock t... more Crack evolution in a rock depends on the mineralogy, microstructure and fabric of specific rock type. This study aims to investigate how mineralogy and grain shape affect the microcrack initiation and propagation of granite rock, which contains plagioclase, quartz, k-feldspar, biotite and amphibole, during uniaxial compression loading. Physico-mechanical properties and microcrack features such as linear microcrack density (LMD) and microcrack type were investigated. By acoustic emission (AE) measurements, damage stress thresholds were identified. Then, crack characteristics of a fresh sample were compared with the samples that were loaded until damage threshold stresses. The results demonstrate that at an early stage of loading, pre-existing microcracks growth and LMD of intergranular crack increase. In the elastic phase, all microcracks types increase at the same rate. When the loading reaches to the strength limit of the sample, the total LMD reduced, because cracks start to coalesce and form new and large transgranular microcrack. Investigating crack propagation in mineral shows that at first, microcrack generates in biotite and at last in quartz. Plagioclase has the highest LMD and microcracks usually formed within the cleavage plane, but alteration and inclusions of tiny minerals can drastically change the LMD and orientation of microcracks. Biotite can terminate or let the microcrack to pass through the crystal based on the orientation of the microcrack plane and cleavage microcrack within the mineral. Furthermore, crystals with an aspect ratio higher than two have higher LMD. By getting close to the uniaxial compression strength, more microcracks appear close to the grain boundary which increases the circularity of the grain.
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