The goal of this study was to compare the predicted void content with the actual void content of pervious concrete cylinders. All pervious concrete systems are designed with a void content in mind to facilitate a spec...The goal of this study was to compare the predicted void content with the actual void content of pervious concrete cylinders. All pervious concrete systems are designed with a void content in mind to facilitate a specific permeability;however, due to variable placing techniques and inherent issues with the material, the actual in place void content often varies from designed. This study quantifies this difference and attempts to develop a correction factor, such that design values are more approximate to in place pervious concrete systems. The analysis included multiple mixtures with three design void contents (15%, 25%, 35%), two aggregate types (angular and rounded), and three different water-to-cement ratios (0.33, 0.37, 0.41). These samples were methodically designed to contain a desired void ratio, then casted in the laboratory, in which the compaction of each sample was controlled for consistency. Following casting, the in-place void content was determined using ASTM C1754 and compared to the predicted. The difference was then averaged to create a correction factor requiring more or less cement paste, which was used to redesign the mixtures. The new mixtures were then compared to the predicted void content. The results of this study show that initial designs can vary from 3% - 15% on average from initial designed void content and that a correction factor can be used to obtain within 3% on average of the target void ratios.展开更多
Brittle fracture and its relationship to deformation and strength have been a fundamental area of research in rock mechanics.This paper presents an expanded pore-emanated cracking model to better understand the fractu...Brittle fracture and its relationship to deformation and strength have been a fundamental area of research in rock mechanics.This paper presents an expanded pore-emanated cracking model to better understand the fracture behaviors and predict the compressive strength of sedimentary rocks.This proposed model is developed to account for a triaxial compression condition using the triaxial compression test results on sandstone,limestone and siltstone samples from Wyoming,USA and experimental data on sedimentary rocks collected from published literature.The normalized critical crack length is determined from the proposed model through which the peak compressive strength is estimated when the stress intensity at the crack tip reaches a critical value called the fracture toughness.Results indicate that the rock porosity and pore radius have an inverse relationship with the compressive strength.Adopting the porosity-permeability relationship,the pore radius is calculated in terms of porosity and grain size.Next,the effect of grain size is implicitly included in the model and negatively correlated with the compressive strength.Moreover,a new approach is proposed for the estimation of fracture toughness based on the pore radius and confining pressure.The predicted compressive strengths from the proposed model show a good agreement with the measured strengths with a mean bias(i.e.average ratio of the measured to predicted strengths)of 1.014.The influence ofφand K_(IC)onσ1 was thoroughly studied using parametric study.The study concludes that the effect ofφis more prominent than K_(IC)onσ1.At a constant porosity of 0.1,the stress ratio decreases from 0.0082 to 0.0078 when K_(IC)increases from 0.1 to 0.2,indicating a 5%decrease in stress ratio.Whereas,at a constant K_(IC)of 0.1,the stress ratio increases from 0.0082 to 0.014 when the porosity increases from 0.1 to 0.2,indicating 71%increases in stress ratio and therefore compressive strength.展开更多
Under cyclic loading,particle breakage occurs at gravelly soil-structure interface,resulting in the decrease of interface strength and the increase of normal displacement.Based on the theory of critical state soil mec...Under cyclic loading,particle breakage occurs at gravelly soil-structure interface,resulting in the decrease of interface strength and the increase of normal displacement.Based on the theory of critical state soil mechanics,the modified Cam-Clay model(MCC)was extended to the plane strain condition of the interface,the state parameter was introduced and the influence of particle breakage on the critical state line was considered,and the cyclic constitutive model for gravelly soil-structure interface considering particle breakage was established by using the non-associated flow rule.Then,the established cyclic constitutive model was used to simulate large-scale cycle direct shear tests of Zipingpu rockfill-steel interface and Zipingpu rockfill-concrete interface under constant normal load(CNL)and constant normal stiffness(CNS),respectively.The simulation results show that under the CNL cyclic loading path,there is little difference between the cyclic shear stress considering particle breakage and that without particle breakage,but the normal displacement considering particle breakage is larger than that without particle breakage,and the difference increases with the increasing number of cycles and normal stress;Under the CNS cyclic loading path,with the increase of the number of cycles,the cyclic shear stress and cyclic normal stress considering particle breakage is significantly smaller than that without particle breakage,and the shear contraction of normal displacement becomes more obvious.In general,the simulation results are closer to the experimental results when particle breakage is considered.展开更多
文摘The goal of this study was to compare the predicted void content with the actual void content of pervious concrete cylinders. All pervious concrete systems are designed with a void content in mind to facilitate a specific permeability;however, due to variable placing techniques and inherent issues with the material, the actual in place void content often varies from designed. This study quantifies this difference and attempts to develop a correction factor, such that design values are more approximate to in place pervious concrete systems. The analysis included multiple mixtures with three design void contents (15%, 25%, 35%), two aggregate types (angular and rounded), and three different water-to-cement ratios (0.33, 0.37, 0.41). These samples were methodically designed to contain a desired void ratio, then casted in the laboratory, in which the compaction of each sample was controlled for consistency. Following casting, the in-place void content was determined using ASTM C1754 and compared to the predicted. The difference was then averaged to create a correction factor requiring more or less cement paste, which was used to redesign the mixtures. The new mixtures were then compared to the predicted void content. The results of this study show that initial designs can vary from 3% - 15% on average from initial designed void content and that a correction factor can be used to obtain within 3% on average of the target void ratios.
基金support from the Wyoming Department of Transportation under the Grant No.RS09220 and Mountain Plains Consortium.
文摘Brittle fracture and its relationship to deformation and strength have been a fundamental area of research in rock mechanics.This paper presents an expanded pore-emanated cracking model to better understand the fracture behaviors and predict the compressive strength of sedimentary rocks.This proposed model is developed to account for a triaxial compression condition using the triaxial compression test results on sandstone,limestone and siltstone samples from Wyoming,USA and experimental data on sedimentary rocks collected from published literature.The normalized critical crack length is determined from the proposed model through which the peak compressive strength is estimated when the stress intensity at the crack tip reaches a critical value called the fracture toughness.Results indicate that the rock porosity and pore radius have an inverse relationship with the compressive strength.Adopting the porosity-permeability relationship,the pore radius is calculated in terms of porosity and grain size.Next,the effect of grain size is implicitly included in the model and negatively correlated with the compressive strength.Moreover,a new approach is proposed for the estimation of fracture toughness based on the pore radius and confining pressure.The predicted compressive strengths from the proposed model show a good agreement with the measured strengths with a mean bias(i.e.average ratio of the measured to predicted strengths)of 1.014.The influence ofφand K_(IC)onσ1 was thoroughly studied using parametric study.The study concludes that the effect ofφis more prominent than K_(IC)onσ1.At a constant porosity of 0.1,the stress ratio decreases from 0.0082 to 0.0078 when K_(IC)increases from 0.1 to 0.2,indicating a 5%decrease in stress ratio.Whereas,at a constant K_(IC)of 0.1,the stress ratio increases from 0.0082 to 0.014 when the porosity increases from 0.1 to 0.2,indicating 71%increases in stress ratio and therefore compressive strength.
基金supported by the National Natural Science Foundation of China(Grant Nos.51922024,52078085 and 52178313)。
文摘Under cyclic loading,particle breakage occurs at gravelly soil-structure interface,resulting in the decrease of interface strength and the increase of normal displacement.Based on the theory of critical state soil mechanics,the modified Cam-Clay model(MCC)was extended to the plane strain condition of the interface,the state parameter was introduced and the influence of particle breakage on the critical state line was considered,and the cyclic constitutive model for gravelly soil-structure interface considering particle breakage was established by using the non-associated flow rule.Then,the established cyclic constitutive model was used to simulate large-scale cycle direct shear tests of Zipingpu rockfill-steel interface and Zipingpu rockfill-concrete interface under constant normal load(CNL)and constant normal stiffness(CNS),respectively.The simulation results show that under the CNL cyclic loading path,there is little difference between the cyclic shear stress considering particle breakage and that without particle breakage,but the normal displacement considering particle breakage is larger than that without particle breakage,and the difference increases with the increasing number of cycles and normal stress;Under the CNS cyclic loading path,with the increase of the number of cycles,the cyclic shear stress and cyclic normal stress considering particle breakage is significantly smaller than that without particle breakage,and the shear contraction of normal displacement becomes more obvious.In general,the simulation results are closer to the experimental results when particle breakage is considered.
