Electrical measurement was employed to investigate the early hydration characteristics of cement pastes with different dosages of superplasticizer in the same W/C ratio. The hyperbolic method was applied to analyze th...Electrical measurement was employed to investigate the early hydration characteristics of cement pastes with different dosages of superplasticizer in the same W/C ratio. The hyperbolic method was applied to analyze the electrical resistivity development. The peak point （Ph） on the hyperbolic curve could be easily read. The time （th） to reach the point Ph had strong relations with the setting time. th was delayed with the increment of the dosage of superplasticizer. The time th was used to plot the relationship between the initial setting time and final setting time. The hyperbolic equation was established to predict the ultimate resistivity. The retardation effect of the superplasticizer was confirmed in the same W/C ratio by setting time and isothermal heat evolution.展开更多
Three types of pure geopolymer pastes （poly-sialate PS, poly- sialate-siloxo PSS, and poly- sialate-siloxo PSDS） were first prepared by alkali （NaOH and KOH） activated metakaolin. Then a void space network was emp...Three types of pure geopolymer pastes （poly-sialate PS, poly- sialate-siloxo PSS, and poly- sialate-siloxo PSDS） were first prepared by alkali （NaOH and KOH） activated metakaolin. Then a void space network was employed to simulate the 3-D pore-throat distribution across the unit cell of the various hardened geopolymer pastes with reference to their experimental mercury intrusion curves. Based on the simulated 3-D pore-throat structure models, a wide range of pore-level properties such as porosity, connectivity, permeability and tortuosity of various geopolymer pastes were calculated. The 3-D structural model and calculated parameters showed that most of the pores in Na-PS geopolymer paste was very small size pores ranging from 0 to 100 nm. A few very large pores were spread amongst the small pores, resulting in a very high penetration pressure, permeability resistance. Unlike Na-PS geopolymer paste, pore size with medium size of Na-PSS, K-PS and K-PSS geopolymer pastes distributed uniformly across the unit cell, and the size changes of adjacent pores in the 3 geopolymer pastes were little, producing higher penetration pressure, lower permeability, smaller connectivity and larger tortuosity. In contrast, pores in Na-PSDS and K-PSDS geopolymer pastes were relatively large and distributed concentratively, which caused samples to be easily penetrated by mercury, methane and nitrogen etc under relatively low pressures.展开更多
External bonding of fiber reinforced polymer （FRP） composites on the concrete structures has been proved to be an effective and efficient way to strengthen concrete structures. For a FRP strengthened concrete beam, ...External bonding of fiber reinforced polymer （FRP） composites on the concrete structures has been proved to be an effective and efficient way to strengthen concrete structures. For a FRP strengthened concrete beam, it is usually observed that the failure occurs in the concrete and a thin layer of concrete is attached on the surface of the debonded FRP plate. To study the debond behavior between concrete and FRP composites, an analytical model based on the three-parameter model is developed to study the debonding behavior for the FRP-to-concrete joint under pure shearing. Then, nonlinear FEM analysis is conducted to verify the PrOposed analytical model. The FEM results shows good agreement with the results from the model. Finally, with the analytical model, sensitivity analyses are performed to study the effect of the interracial parameters or the ~eometric parameters on the debondin~ behavior.展开更多
The bonding status and chemical environment of SiO4 and AlO4 tetrahedras of three types of geopolymeric products were systematically investigated by infrared spectroscopy. The relationship between amorphous geopolymer...The bonding status and chemical environment of SiO4 and AlO4 tetrahedras of three types of geopolymeric products were systematically investigated by infrared spectroscopy. The relationship between amorphous geopolymeric products and zeolite crystals with the same overall chemical compositions was also discussed. The infrared evidence shows that SiO4 tetrahedra is partially bonded by AlO4 during the hydration process of geopolymeric cement. The two types of tetrahedras jointly construct the three dimensional framework structures of the geopolymeric products. The mutual transformation between geopolymeric products and corresponding zeolite crystals will take place once the reaction condition is suitable, which reveals that the nature ofgeopolymeric products are probably the amorphous equivalent of the corresponding zeolite crystals.展开更多
Backscattered electron images（BSE） obtained by scanning electron microscope was used to quantitatively characterize the microstructure of interfacial transition zone（ITZ） in concrete. Influences of aggregate size...Backscattered electron images（BSE） obtained by scanning electron microscope was used to quantitatively characterize the microstructure of interfacial transition zone（ITZ） in concrete. Influences of aggregate size（5, 10, 20, and 30 mm）, water to cement ratio（0.23, 0.35 and 0.53） and curing time（from 3d to 90d） on the microstructure of interfacial transition zone between coarse aggregate and bulk cement matrix were investigated. The volume percentage of detectable porosity and unhydrated cement in ITZ was quantitatively analyzed and compared with that in the matrix of various concretes. Nanoindentation technology was applied to obtain the elastic properties of ITZ and matrix, and the elastic modulus of concrete was then calculated based on the Lu ＆ Torquato model and self-consistence scheme by using the ITZ thickness and elastic modulus obtained from this investigation. The experimental results demonstrated that the microstructure and thickness of ITZ in concrete vary with a variety of factors, like aggregate size, water to cement ratio and curing time. The relative low elastic properties of ITZ should be paid attention to, especially for early age concrete.展开更多
In order to make clear the interaction mechanism of single component epoxy in cementitious environment, the interaction between epoxy resin and active silanol, epoxy resin and alkali was investigated From solid-state ...In order to make clear the interaction mechanism of single component epoxy in cementitious environment, the interaction between epoxy resin and active silanol, epoxy resin and alkali was investigated From solid-state 13C NMR and FT-IR tests, it is confirmed that silanol group can initiate epoxy resin. Test results have also revealed that alkali as the dominant product of cement hydration can open the epoxide ring making epoxy harden.展开更多
Single-component epoxy cement system is an interesting material used in construction engineering, and it is different from traditional two-component epoxy-cement system. We studied the interaction mechanism of single-...Single-component epoxy cement system is an interesting material used in construction engineering, and it is different from traditional two-component epoxy-cement system. We studied the interaction mechanism of single-component epoxy-cement system only in the range of macro mechanical performances, and used the cement and single-component epoxy directly to investigate the interaction between the both. Solidstate 13 C NMR, FT-IR, Raman spectroscopy and XRD were employed to trace the change of the system. Results showed that the epoxide rings in cementitious environment had been opened by cement ingredients. It was true that single-component epoxy could be used as reactive additive in cementitious system.展开更多
Endothelial cell therapy has been implicated to enhance tissue regeneration and vascularization in ischemic kidney. However, no published study has yet examined direct effects of endothelial cell treatment in kidney r...Endothelial cell therapy has been implicated to enhance tissue regeneration and vascularization in ischemic kidney. However, no published study has yet examined direct effects of endothelial cell treatment in kidney recovery. This study investigated the therapeutic efficacy of endothelial cells in a mouse model with acute kidney injury (AKI). Thus, human embryonic stem cells-derived endothelial cells (hESC-ECs) labeled with a reporter system encoding a double fusion reporter gene for firefly luciferase (Fluc) and green fluorescent protein (GFP) were characterized by Fluc imaging and immunofluoresence staining. Cultured hESC-ECs (1×106) were injected into ischemic kidney shortly after AKI. Survival of the transplanted hESC-ECs was monitored in vivo from day 1 to 14 after endothelial cell transplantation and potential impact of hESC-EC treatment on renal regeneration was assessed by histological analyses. We report that a substantial level of bioluminescence activity was detected 24 h after hESC-EC injection followed by a gradual decline from 1 to 14 d. Human ESC-ECs markedly accelerated kidney cell proliferation in response to ischaemia-induced damage, indicated by an elevated number of BrdU+ cells. Co-expression of Sca-1, a kidney stem cell proliferation marker, and BrdU further suggested that the observed stimulation in renal cell regeneration was, at least in part, due to increased proliferation of renal resident stem cells especially within the medullary cords and arteriole. Differentiation of hESC-ECs to smooth muscle cells was also observed at an early stage of kidney recovery. In summary, our results suggest that endothelial cell therapy facilitates kidney recovery by promoting vascularization, trans-differentiation and endogenous renal stem cell proliferation in AKI.展开更多
Experimental investigation was conducted to characterize the responses of pseudo-ductile cementitious composites (PDCCs) when subjected to uniaxial and biaxial compression.The PDCCs is a class of fiber reinforced ceme...Experimental investigation was conducted to characterize the responses of pseudo-ductile cementitious composites (PDCCs) when subjected to uniaxial and biaxial compression.The PDCCs is a class of fiber reinforced cementitious composites with ultra-high ductility by using a low volume fraction (2%) of polyvinyl alcohol (PVA) fiber.Two different strength grades of PDCC were examined with cubic specimen size of 100 mm in the tests.The specimens were loaded with a servo-hydraulic jack at different stress ratios.The principle stresses and strains of the specimens were recorded,and the failure modes with various stress states were examined.The test results indicated that the ultimate strength of PDCCs increased due to the lateral confinement in the other principal stress direction,and the maximum ultimate strength occurred at the biaxial stress ratio of 0.25,which was very different from common concrete material.For the PDCC specimens,the biaxial strength may be lower than the uniaxial strength when subjected to biaxial compression with the stress ratio of 1.0,and the failure mode showed a shear-type failure because of the bridging effect of fibers.Finally,a failure criterion was proposed for PDCCs under biaxial compression.展开更多
基金the National Natural Science Foundation of China(No.50778078)
文摘Electrical measurement was employed to investigate the early hydration characteristics of cement pastes with different dosages of superplasticizer in the same W/C ratio. The hyperbolic method was applied to analyze the electrical resistivity development. The peak point （Ph） on the hyperbolic curve could be easily read. The time （th） to reach the point Ph had strong relations with the setting time. th was delayed with the increment of the dosage of superplasticizer. The time th was used to plot the relationship between the initial setting time and final setting time. The hyperbolic equation was established to predict the ultimate resistivity. The retardation effect of the superplasticizer was confirmed in the same W/C ratio by setting time and isothermal heat evolution.
基金Funded by the Major State Basic Research Development Program of China(973 Program)(No.2015CB655102)National Natural Science Foundation of China(No.51378116)PhD Programs Foundation of Ministry of Education of China(No.20120092110037)
文摘Three types of pure geopolymer pastes （poly-sialate PS, poly- sialate-siloxo PSS, and poly- sialate-siloxo PSDS） were first prepared by alkali （NaOH and KOH） activated metakaolin. Then a void space network was employed to simulate the 3-D pore-throat distribution across the unit cell of the various hardened geopolymer pastes with reference to their experimental mercury intrusion curves. Based on the simulated 3-D pore-throat structure models, a wide range of pore-level properties such as porosity, connectivity, permeability and tortuosity of various geopolymer pastes were calculated. The 3-D structural model and calculated parameters showed that most of the pores in Na-PS geopolymer paste was very small size pores ranging from 0 to 100 nm. A few very large pores were spread amongst the small pores, resulting in a very high penetration pressure, permeability resistance. Unlike Na-PS geopolymer paste, pore size with medium size of Na-PSS, K-PS and K-PSS geopolymer pastes distributed uniformly across the unit cell, and the size changes of adjacent pores in the 3 geopolymer pastes were little, producing higher penetration pressure, lower permeability, smaller connectivity and larger tortuosity. In contrast, pores in Na-PSDS and K-PSDS geopolymer pastes were relatively large and distributed concentratively, which caused samples to be easily penetrated by mercury, methane and nitrogen etc under relatively low pressures.
基金the National Basic Research Program of China (973 Project) (No. 2009CB623200)National Natural Science Foundation of China (No. 50808043)+1 种基金the Doctoral Program of Higher Education of China (No. 20070286024)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘External bonding of fiber reinforced polymer （FRP） composites on the concrete structures has been proved to be an effective and efficient way to strengthen concrete structures. For a FRP strengthened concrete beam, it is usually observed that the failure occurs in the concrete and a thin layer of concrete is attached on the surface of the debonded FRP plate. To study the debond behavior between concrete and FRP composites, an analytical model based on the three-parameter model is developed to study the debonding behavior for the FRP-to-concrete joint under pure shearing. Then, nonlinear FEM analysis is conducted to verify the PrOposed analytical model. The FEM results shows good agreement with the results from the model. Finally, with the analytical model, sensitivity analyses are performed to study the effect of the interracial parameters or the ~eometric parameters on the debondin~ behavior.
基金Jiangsu Province Natural Science Foundation(No.BK2006555,BK2005216)the West Communication Construction Foundation(No.2006ZB12)the Nanjing Hydraulic Research Institute Opening and Flowing Research Foundation(No.Yk90508)
文摘The bonding status and chemical environment of SiO4 and AlO4 tetrahedras of three types of geopolymeric products were systematically investigated by infrared spectroscopy. The relationship between amorphous geopolymeric products and zeolite crystals with the same overall chemical compositions was also discussed. The infrared evidence shows that SiO4 tetrahedra is partially bonded by AlO4 during the hydration process of geopolymeric cement. The two types of tetrahedras jointly construct the three dimensional framework structures of the geopolymeric products. The mutual transformation between geopolymeric products and corresponding zeolite crystals will take place once the reaction condition is suitable, which reveals that the nature ofgeopolymeric products are probably the amorphous equivalent of the corresponding zeolite crystals.
基金Funded by the National Natural Science Foundation of China(No.51178105)the Major State Basic Research Development Program of China(973 Program)(No.2015CB655104)the Collaborative Innovation Centre for Advanced Civil Engineering Materials
文摘Backscattered electron images（BSE） obtained by scanning electron microscope was used to quantitatively characterize the microstructure of interfacial transition zone（ITZ） in concrete. Influences of aggregate size（5, 10, 20, and 30 mm）, water to cement ratio（0.23, 0.35 and 0.53） and curing time（from 3d to 90d） on the microstructure of interfacial transition zone between coarse aggregate and bulk cement matrix were investigated. The volume percentage of detectable porosity and unhydrated cement in ITZ was quantitatively analyzed and compared with that in the matrix of various concretes. Nanoindentation technology was applied to obtain the elastic properties of ITZ and matrix, and the elastic modulus of concrete was then calculated based on the Lu ＆ Torquato model and self-consistence scheme by using the ITZ thickness and elastic modulus obtained from this investigation. The experimental results demonstrated that the microstructure and thickness of ITZ in concrete vary with a variety of factors, like aggregate size, water to cement ratio and curing time. The relative low elastic properties of ITZ should be paid attention to, especially for early age concrete.
基金Funded by the National Natural Science Founda-tion of China(No.51578290)
文摘In order to make clear the interaction mechanism of single component epoxy in cementitious environment, the interaction between epoxy resin and active silanol, epoxy resin and alkali was investigated From solid-state 13C NMR and FT-IR tests, it is confirmed that silanol group can initiate epoxy resin. Test results have also revealed that alkali as the dominant product of cement hydration can open the epoxide ring making epoxy harden.
基金Funded by the National Natural Science Foundation of China(No.51578290)
文摘Single-component epoxy cement system is an interesting material used in construction engineering, and it is different from traditional two-component epoxy-cement system. We studied the interaction mechanism of single-component epoxy-cement system only in the range of macro mechanical performances, and used the cement and single-component epoxy directly to investigate the interaction between the both. Solidstate 13 C NMR, FT-IR, Raman spectroscopy and XRD were employed to trace the change of the system. Results showed that the epoxide rings in cementitious environment had been opened by cement ingredients. It was true that single-component epoxy could be used as reactive additive in cementitious system.
基金supported by the National Key Scientific Program of China(2011CB964903)the National Natural Science Foundation of China(31071308,30970746,81220108015)Doctoral Fund of Ministry of Education of China(20090031110024)
文摘Endothelial cell therapy has been implicated to enhance tissue regeneration and vascularization in ischemic kidney. However, no published study has yet examined direct effects of endothelial cell treatment in kidney recovery. This study investigated the therapeutic efficacy of endothelial cells in a mouse model with acute kidney injury (AKI). Thus, human embryonic stem cells-derived endothelial cells (hESC-ECs) labeled with a reporter system encoding a double fusion reporter gene for firefly luciferase (Fluc) and green fluorescent protein (GFP) were characterized by Fluc imaging and immunofluoresence staining. Cultured hESC-ECs (1×106) were injected into ischemic kidney shortly after AKI. Survival of the transplanted hESC-ECs was monitored in vivo from day 1 to 14 after endothelial cell transplantation and potential impact of hESC-EC treatment on renal regeneration was assessed by histological analyses. We report that a substantial level of bioluminescence activity was detected 24 h after hESC-EC injection followed by a gradual decline from 1 to 14 d. Human ESC-ECs markedly accelerated kidney cell proliferation in response to ischaemia-induced damage, indicated by an elevated number of BrdU+ cells. Co-expression of Sca-1, a kidney stem cell proliferation marker, and BrdU further suggested that the observed stimulation in renal cell regeneration was, at least in part, due to increased proliferation of renal resident stem cells especially within the medullary cords and arteriole. Differentiation of hESC-ECs to smooth muscle cells was also observed at an early stage of kidney recovery. In summary, our results suggest that endothelial cell therapy facilitates kidney recovery by promoting vascularization, trans-differentiation and endogenous renal stem cell proliferation in AKI.
基金supported by the National Natural Science Foundation of China (Grant No. 51278118)the National Basic Research Program of China ("973" Program) (Grant No. 2009CB623200)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Experimental investigation was conducted to characterize the responses of pseudo-ductile cementitious composites (PDCCs) when subjected to uniaxial and biaxial compression.The PDCCs is a class of fiber reinforced cementitious composites with ultra-high ductility by using a low volume fraction (2%) of polyvinyl alcohol (PVA) fiber.Two different strength grades of PDCC were examined with cubic specimen size of 100 mm in the tests.The specimens were loaded with a servo-hydraulic jack at different stress ratios.The principle stresses and strains of the specimens were recorded,and the failure modes with various stress states were examined.The test results indicated that the ultimate strength of PDCCs increased due to the lateral confinement in the other principal stress direction,and the maximum ultimate strength occurred at the biaxial stress ratio of 0.25,which was very different from common concrete material.For the PDCC specimens,the biaxial strength may be lower than the uniaxial strength when subjected to biaxial compression with the stress ratio of 1.0,and the failure mode showed a shear-type failure because of the bridging effect of fibers.Finally,a failure criterion was proposed for PDCCs under biaxial compression.
