The aim of this paper is to investigate the effect of nitrite intercalated Mg-Al layered double hydroxides(Mg-Al LDH-NO_(2))on mortar durability under the coexisting environment of Cl−and SO_(4)^(2-).Cl−and SO_(4)^(2-...The aim of this paper is to investigate the effect of nitrite intercalated Mg-Al layered double hydroxides(Mg-Al LDH-NO_(2))on mortar durability under the coexisting environment of Cl−and SO_(4)^(2-).Cl−and SO_(4)^(2-) binding properties of Mg-Al LDH-NO_(2) in simulated concrete pore solutions,Cl−and SO_(4)^(2-) diffusion properties of mortars with Mg-Al LDHNO 2 were examined.The steel corrosion and resistance of mortar against SO_(4)^(2-) attack were also evaluated.The results indicate that Mg-Al LDH-NO_(2) can effectively adsorb the Cl−and SO_(4)^(2-) in simulated concrete pore solution,and inhibit the diffusion of Cl−and SO_(4)^(2-) into cement mortars.The presence of SO_(4)^(2-) can greatly affect the uptake amount of Cl−,and there is a coupled effect of Cl−and SO_(4)^(2-) on their penetration into mortar specimens.In addition,Mg-Al LDH-NO_(2) can greatly upgrade the resistance of mortars against SO_(4)^(2-) attack and well prevent the steel from corrosion.However,Cl−will aggravate the SO_(4)^(2-) attack and SO_(4)^(2-) can initially decrease and then increase the steel corrosion.展开更多
To evaluate the effect of treating long cracks with the impact crack-closure retrofit(ICR)technique,three rib-to-deck welded specimens with a crack length of about 100 mm were tested.The metallographic structure,crack...To evaluate the effect of treating long cracks with the impact crack-closure retrofit(ICR)technique,three rib-to-deck welded specimens with a crack length of about 100 mm were tested.The metallographic structure,crack section,crack propagation life,and stress variation were analyzed.Finite-element models were also developed,and some optimal values of certain parameters are suggested according to the simulated results.The results show that new crack sources are generated on both sides of the ICR-treated region because of the stress distribution.The fatigue lives of cracked specimens with long cracks are significantly improved by the technique.Considerable residual compressive stress is also induced,and so it is suggested that the optimal impact angle to be applied to real bridges should be 70°.The stress at the weld root is distributed uniformly with the crack closed,and the optimal crack-closure depth is 4 mm.To evaluate the effect of different crack-closure depths in tests,it is recommended that a hot-spot stress method which is extrapolated by three reference points should be adopted.展开更多
Graphene and its derivatives are two-dimensional nanomaterials with exceptional physical and chemical properties.Research has shown that their addition can counter the inherent deficiencies of cementbased composites,i...Graphene and its derivatives are two-dimensional nanomaterials with exceptional physical and chemical properties.Research has shown that their addition can counter the inherent deficiencies of cementbased composites,including low tensile strength,poor toughness,and high susceptibility to cracking.However,because of its high specific surface area and the van der Waals force between layers,graphene is prone to agglomerate in the cement matrix which can make the properties worse.Hence,improving the graphene dispersion is essential.The surface structure and properties of graphene and its derivatives are first introduced,and the different methods for their dispersion in cement-based materials are reviewed.Their effects on the mechanical properties and durability of cement-based materials are then summarized.Based on these results,the microscopic and nanoscopic mechanisms of the way graphene and its derivatives affect cement-based materials are elaborated.Current problems and future trends in this research area are then considered.展开更多
Phosphorous slag （PHS）, ground granulated blast-furnace slag （GGBS） and fly ash （FA） were used as replacements of Portland cement to modify the microstruc^xe of recycled aggregate concrete （RAC）. A new manufac...Phosphorous slag （PHS）, ground granulated blast-furnace slag （GGBS） and fly ash （FA） were used as replacements of Portland cement to modify the microstruc^xe of recycled aggregate concrete （RAC）. A new manufacturing method named ＂W3T4＂ was proposed to improve the performances of interracial transition zone （ITZ） between recycled aggregate and mortar. The mechanical properties and the durability of RAC were tested, which show that this new manufacturing method improves the properties of RAC, and the GGBS with finest size makes a great contribution to the performance of RAC due to its better filling effect and much earlier pozzolanic reaction. Combined with GGBS, the effects of PHS on the retardation of setting time can be alleviated and the synergistic effect helps to make a more compact RAC. For the RAC with 25% of the recycled aggregate （RA） replacement and 10% PHS ＋ 10% GGBS additives, the compressive strength increases by 25.4%, but the permeability decreases by 64.3% with respect to the reference concrete made with nature aggregates. The micro-mechanisms of these improvements were investigated by the scanning electron microscope （SEM）. The SEM images show that the new manufacturing method, adding superfine pozzolanic powders and super-plasticizer benefits, makes a much denser ITZ in RAC.展开更多
Workability and mechanical properties of steel slag green concrete with different types of steel slag and different dosages of admixtures were investigated. The effectiveness of steel slag powder on suppressing alkali...Workability and mechanical properties of steel slag green concrete with different types of steel slag and different dosages of admixtures were investigated. The effectiveness of steel slag powder on suppressing alkali aggregate reaction(AAR) expansion was assessed using the method of ASTM C441 and accelerated test method. Experimental results show that mechanical properties can be improved further due to the synergistic effect and mutual activation when compound mineral admixtures with steel slag powder and blast-furnace slag powder are mixed into concrete. In addition,about 50% decrease in expansion rate of mortar bars with mineral admixtures can be achieved in AAR tests. Mineral admixtures with steel slag powder as partial replacement for Portland cement in concrete is an effective means for controlling expansion due to AAR.展开更多
Bidirectional electromigration rehabilitation(BIEM)is a novel electrochemical rehabilitation method involving the injection of inhibitors into steel bar surface.The BIEM effect and hydrogen embrittlement(HE)risk depen...Bidirectional electromigration rehabilitation(BIEM)is a novel electrochemical rehabilitation method involving the injection of inhibitors into steel bar surface.The BIEM effect and hydrogen embrittlement(HE)risk depend on the electrochemical parameters(current density and duration)and operating condition(stress level and concrete cover thickness)of reinforced concrete structures.Experiments were performed in this study to investigate the relationships between the aforementioned factors.For a small current density group,a linear relationship was established between electric flux and chloride extraction.For a large current density group,the reasonable current density,stress level,and treatment time were obtained.Finally,the querying method of electrochemical parameters combined with treatment time and current density was proposed.展开更多
Lead-free low melting glasses,ZnO-CuO-Bi_(2)O_(3)-B_(2)O_(3)-SiO_(2)system,with fixed contents of 15 mol%CuO and 20 mol%Bi_(2)O_(3),were prepared by using melt cooling method.Structure and thermal properties of the gl...Lead-free low melting glasses,ZnO-CuO-Bi_(2)O_(3)-B_(2)O_(3)-SiO_(2)system,with fixed contents of 15 mol%CuO and 20 mol%Bi_(2)O_(3),were prepared by using melt cooling method.Structure and thermal properties of the glasses were studied by using X-ray diffractometer(XRD),infrared spectrometer(FIT-IR),thermal dilatometer and differential thermal analyzer(DTA).Chemical durability of the glasses was studied by using dissolution rate method.Wettability of glasses on substrate was tested by using button sintering experiment.It is found that alkaline resistance of the glass solders is lower than that of plate glass and the water resistance is comparable with that of plate glass.The sealing temperatures are Ts=445-490℃,while the average thermal expansion coefficient from room temperature to 300℃is in the range of(65-82)×10^(−7)℃^(−1).At sealing temperature,the glass solders have good wettability on plate glass or alumina substrate.They are not crystallized even sintered at the sealing temperature for 30 min.The solder glasses are suitable for sealing plate glass,alumina and other inorganic non-metallic materials.展开更多
Hydraulic cylinder is a primary component of the hydraulic valve systems.The numerical study of hydraulic cylinder to evaluate the stress analysis,the life assessment and the performance of operation characteristics i...Hydraulic cylinder is a primary component of the hydraulic valve systems.The numerical study of hydraulic cylinder to evaluate the stress analysis,the life assessment and the performance of operation characteristics in hydraulic cylinder were described.The calculation of safety factor,fatigue life,piston chamber pressure,rod chamber pressure and the change of velocity of piston with flow time after the beginning of hydraulic cylinder were incorporated.Numerical analysis was performed using the commercial CFD code,ANSYS with unsteady,dynamic mesh model,two-way FSI(fluid-structure interaction)method and k-εturbulent model.The internal pressure in hydraulic cylinder through stress analysis show higher than those of the yield strength.展开更多
Effects of Zn/P ratio on the structures and properties of glasses with the general composition of （80-x）ZnO-20Fe2O3-xP2O5 （x=40, 45, 50, 55, 60） （molar fraction, %） were investigated. Glass structure was measure...Effects of Zn/P ratio on the structures and properties of glasses with the general composition of （80-x）ZnO-20Fe2O3-xP2O5 （x=40, 45, 50, 55, 60） （molar fraction, %） were investigated. Glass structure was measured by infrared absorption spectrum. Glass density （/9） was measured by the Archimedes method. Coefficients of thermal expansion （a） and characterization temperature were obtained by a dilatometer. Water durability of each glass was estimated from the dissolution rate （DR）in water at 90 ℃ for 24 h. With increasing Zn/P ratio, water durability of zinc-iron phosphate glasses increases dramatically without large increase in the characterization temperature. （80-x）ZnO-20Fe2O3-xP2O5 glasses with 0.3≤Zn/P≤0.5 are suit for low-to-mid temperature sealing application for substrates with a〈8.0× 10^-6℃^-1.展开更多
Invading track of chloride ions and chloride ion distribution rule in cement-based materials were investigated by partially soaking in 3.5% （mass fraction） NaCl solution and fully immerging in 3.5% and 5.0% （mass f...Invading track of chloride ions and chloride ion distribution rule in cement-based materials were investigated by partially soaking in 3.5% （mass fraction） NaCl solution and fully immerging in 3.5% and 5.0% （mass fraction） NaC1 solution, respectively, and relevant invading mechanisms were discussed. Results indicate that under full immerging condition, the invading track of chloride ions in cement mortar is similar to beeline that is vertical to chloride ion invading direction, and chloride ion content decreases rapidly with the increase of chloride ion invading depth. Under partial soaking condition, the invading track of chloride ion in cement mortar is similar to the shape of concave parabola, and chloride ion content decreases slowly along the lengthway direction of cement mortar samples in the distance of 20-80 mm from the bottom. Lots of chloride ions accumulate in cement mortar surface layer under the effect of capillary rise and evaporation and then invade cement mortar by diffusion effect. Under partial soaking condition, cement mortar is distinguished by four areas, i.e., immerging area, wet area, crystallization area and dry area.展开更多
Fly ash is the most inexpensive cementitious material,and its presence in concrete has increased in recent years because it has become more durable and environmentally friendly.This study examines densified mixture co...Fly ash is the most inexpensive cementitious material,and its presence in concrete has increased in recent years because it has become more durable and environmentally friendly.This study examines densified mixture concrete and the effect of fly ash quality on high-flow,high-strength concrete.Tests show that when the same mixture achieves identical flow standards(slump >250 mm;slump flow >600 mm),the fly ash quality affects the nature of the concrete;additionally,and adding Class F fly ash to concrete(loss on ignition=6%)is more workable than adding Class C fly ash(loss on ignition=3%).However,adding fly ash with a high loss on ignition(9%)to concrete requires a substantial increase in the mixing water and a dose of superplasticizer to achieve the required workability.This reduces the quality of the concrete,which subsequently deteriorates its safety and durability.展开更多
This paper describes a study on the load bearing capacity of newly developed high density sintered metal gears with surface-densification. High density sintered metal gears were hobbed, and then surface-rolled. These ...This paper describes a study on the load bearing capacity of newly developed high density sintered metal gears with surface-densification. High density sintered metal gears were hobbed, and then surface-rolled. These gears were case-carburized after surface-rolling. The effect of surface-rolling on the surface property was examined by measuring porosity and hardness near surfaces of rolled gears. Running tests for these gears were performed. A failure mode and load bearing capacity of high density sintered metal gears and the effects of surface-rolling on the load bearing capacity of sintered metal gears were determined, and the results were compared with those of carburized wrought steel gears and conventional sintered metal gears. The experimental results show that the load bearing capacity of a newly developed high density sintered metal gear with surface-densification is higher than that of a carburized wrought steel gear.展开更多
基金Project(51478164)supported by the National Natural Science Foundation of ChinaProject(BK20181306)supported by Natural Science Foundation of Jiangsu Province,China。
文摘The aim of this paper is to investigate the effect of nitrite intercalated Mg-Al layered double hydroxides(Mg-Al LDH-NO_(2))on mortar durability under the coexisting environment of Cl−and SO_(4)^(2-).Cl−and SO_(4)^(2-) binding properties of Mg-Al LDH-NO_(2) in simulated concrete pore solutions,Cl−and SO_(4)^(2-) diffusion properties of mortars with Mg-Al LDHNO 2 were examined.The steel corrosion and resistance of mortar against SO_(4)^(2-) attack were also evaluated.The results indicate that Mg-Al LDH-NO_(2) can effectively adsorb the Cl−and SO_(4)^(2-) in simulated concrete pore solution,and inhibit the diffusion of Cl−and SO_(4)^(2-) into cement mortars.The presence of SO_(4)^(2-) can greatly affect the uptake amount of Cl−,and there is a coupled effect of Cl−and SO_(4)^(2-) on their penetration into mortar specimens.In addition,Mg-Al LDH-NO_(2) can greatly upgrade the resistance of mortars against SO_(4)^(2-) attack and well prevent the steel from corrosion.However,Cl−will aggravate the SO_(4)^(2-) attack and SO_(4)^(2-) can initially decrease and then increase the steel corrosion.
基金Projects(51478163,51678216)supported by the National Natural Science Foundation of ChinaProject(2017Y09)supported by the Transport Science Research Project of Jiangsu Province,China
文摘To evaluate the effect of treating long cracks with the impact crack-closure retrofit(ICR)technique,three rib-to-deck welded specimens with a crack length of about 100 mm were tested.The metallographic structure,crack section,crack propagation life,and stress variation were analyzed.Finite-element models were also developed,and some optimal values of certain parameters are suggested according to the simulated results.The results show that new crack sources are generated on both sides of the ICR-treated region because of the stress distribution.The fatigue lives of cracked specimens with long cracks are significantly improved by the technique.Considerable residual compressive stress is also induced,and so it is suggested that the optimal impact angle to be applied to real bridges should be 70°.The stress at the weld root is distributed uniformly with the crack closed,and the optimal crack-closure depth is 4 mm.To evaluate the effect of different crack-closure depths in tests,it is recommended that a hot-spot stress method which is extrapolated by three reference points should be adopted.
文摘Graphene and its derivatives are two-dimensional nanomaterials with exceptional physical and chemical properties.Research has shown that their addition can counter the inherent deficiencies of cementbased composites,including low tensile strength,poor toughness,and high susceptibility to cracking.However,because of its high specific surface area and the van der Waals force between layers,graphene is prone to agglomerate in the cement matrix which can make the properties worse.Hence,improving the graphene dispersion is essential.The surface structure and properties of graphene and its derivatives are first introduced,and the different methods for their dispersion in cement-based materials are reviewed.Their effects on the mechanical properties and durability of cement-based materials are then summarized.Based on these results,the microscopic and nanoscopic mechanisms of the way graphene and its derivatives affect cement-based materials are elaborated.Current problems and future trends in this research area are then considered.
基金Project(51178417)supported by the National Natural Science Foundation of ChinaProject(2012R10025)supported by the Qianjiang Talent Plan of Zhejiang Province,China+2 种基金Project(2012HY006B)supported by the Marine Cross-Guide Research Funds of Zhejiang University,ChinaProject(2013FZA4015)supported by the Fundamental Research Funds for the Central Universities,ChinaProject supported by the Department of Construction of Zhejiang Province,China
文摘Phosphorous slag （PHS）, ground granulated blast-furnace slag （GGBS） and fly ash （FA） were used as replacements of Portland cement to modify the microstruc^xe of recycled aggregate concrete （RAC）. A new manufacturing method named ＂W3T4＂ was proposed to improve the performances of interracial transition zone （ITZ） between recycled aggregate and mortar. The mechanical properties and the durability of RAC were tested, which show that this new manufacturing method improves the properties of RAC, and the GGBS with finest size makes a great contribution to the performance of RAC due to its better filling effect and much earlier pozzolanic reaction. Combined with GGBS, the effects of PHS on the retardation of setting time can be alleviated and the synergistic effect helps to make a more compact RAC. For the RAC with 25% of the recycled aggregate （RA） replacement and 10% PHS ＋ 10% GGBS additives, the compressive strength increases by 25.4%, but the permeability decreases by 64.3% with respect to the reference concrete made with nature aggregates. The micro-mechanisms of these improvements were investigated by the scanning electron microscope （SEM）. The SEM images show that the new manufacturing method, adding superfine pozzolanic powders and super-plasticizer benefits, makes a much denser ITZ in RAC.
基金Project(2006BAF02A00) supported by the National Science and Technology Pillar Program during the 11th Five-Year Plan Period of ChinaProject(08-2-1-18-nsh) supported by the Science and Technology Program of Qingdao City, China
文摘Workability and mechanical properties of steel slag green concrete with different types of steel slag and different dosages of admixtures were investigated. The effectiveness of steel slag powder on suppressing alkali aggregate reaction(AAR) expansion was assessed using the method of ASTM C441 and accelerated test method. Experimental results show that mechanical properties can be improved further due to the synergistic effect and mutual activation when compound mineral admixtures with steel slag powder and blast-furnace slag powder are mixed into concrete. In addition,about 50% decrease in expansion rate of mortar bars with mineral admixtures can be achieved in AAR tests. Mineral admixtures with steel slag powder as partial replacement for Portland cement in concrete is an effective means for controlling expansion due to AAR.
基金Projects(51908496,51878610,51820105012,51778577,51638013)supported by the National Natural Science Foundation of ChinaProjects(LY18E080003,LQ19E080011,LQ19E080012,LQ20E080001)supported by the Natural Science Foundation of Zhejiang Province,ChinaProject(2018A610359)supported by the Natural Science Foundation of Ningbo,China。
文摘Bidirectional electromigration rehabilitation(BIEM)is a novel electrochemical rehabilitation method involving the injection of inhibitors into steel bar surface.The BIEM effect and hydrogen embrittlement(HE)risk depend on the electrochemical parameters(current density and duration)and operating condition(stress level and concrete cover thickness)of reinforced concrete structures.Experiments were performed in this study to investigate the relationships between the aforementioned factors.For a small current density group,a linear relationship was established between electric flux and chloride extraction.For a large current density group,the reasonable current density,stress level,and treatment time were obtained.Finally,the querying method of electrochemical parameters combined with treatment time and current density was proposed.
基金National Natural Science Foundation of China(52172070)Jiangxi Provincial Natural Science Foundation(20242BAB25222)Jiangxi Provincial Graduate Innovation Special Fund Project(YC2022-S882 and YC2023-S808).
文摘Lead-free low melting glasses,ZnO-CuO-Bi_(2)O_(3)-B_(2)O_(3)-SiO_(2)system,with fixed contents of 15 mol%CuO and 20 mol%Bi_(2)O_(3),were prepared by using melt cooling method.Structure and thermal properties of the glasses were studied by using X-ray diffractometer(XRD),infrared spectrometer(FIT-IR),thermal dilatometer and differential thermal analyzer(DTA).Chemical durability of the glasses was studied by using dissolution rate method.Wettability of glasses on substrate was tested by using button sintering experiment.It is found that alkaline resistance of the glass solders is lower than that of plate glass and the water resistance is comparable with that of plate glass.The sealing temperatures are Ts=445-490℃,while the average thermal expansion coefficient from room temperature to 300℃is in the range of(65-82)×10^(−7)℃^(−1).At sealing temperature,the glass solders have good wettability on plate glass or alumina substrate.They are not crystallized even sintered at the sealing temperature for 30 min.The solder glasses are suitable for sealing plate glass,alumina and other inorganic non-metallic materials.
基金supported by the International Cooperation on Technology Development Program of the Korea Institute for Advancement of Technology ( KIAT),Republic of Korea ( N0000902)
文摘Hydraulic cylinder is a primary component of the hydraulic valve systems.The numerical study of hydraulic cylinder to evaluate the stress analysis,the life assessment and the performance of operation characteristics in hydraulic cylinder were described.The calculation of safety factor,fatigue life,piston chamber pressure,rod chamber pressure and the change of velocity of piston with flow time after the beginning of hydraulic cylinder were incorporated.Numerical analysis was performed using the commercial CFD code,ANSYS with unsteady,dynamic mesh model,two-way FSI(fluid-structure interaction)method and k-εturbulent model.The internal pressure in hydraulic cylinder through stress analysis show higher than those of the yield strength.
基金Project(7602110340) supported by the Postdoctoral Science Foundation of Central South University, ChinaProject(721500277)supported by the Fundamental Research Funds for the Central Universities of China
文摘Effects of Zn/P ratio on the structures and properties of glasses with the general composition of （80-x）ZnO-20Fe2O3-xP2O5 （x=40, 45, 50, 55, 60） （molar fraction, %） were investigated. Glass structure was measured by infrared absorption spectrum. Glass density （/9） was measured by the Archimedes method. Coefficients of thermal expansion （a） and characterization temperature were obtained by a dilatometer. Water durability of each glass was estimated from the dissolution rate （DR）in water at 90 ℃ for 24 h. With increasing Zn/P ratio, water durability of zinc-iron phosphate glasses increases dramatically without large increase in the characterization temperature. （80-x）ZnO-20Fe2O3-xP2O5 glasses with 0.3≤Zn/P≤0.5 are suit for low-to-mid temperature sealing application for substrates with a〈8.0× 10^-6℃^-1.
基金Project(50678174) supported by the National Natural Science Foundation of China
文摘Invading track of chloride ions and chloride ion distribution rule in cement-based materials were investigated by partially soaking in 3.5% （mass fraction） NaCl solution and fully immerging in 3.5% and 5.0% （mass fraction） NaC1 solution, respectively, and relevant invading mechanisms were discussed. Results indicate that under full immerging condition, the invading track of chloride ions in cement mortar is similar to beeline that is vertical to chloride ion invading direction, and chloride ion content decreases rapidly with the increase of chloride ion invading depth. Under partial soaking condition, the invading track of chloride ion in cement mortar is similar to the shape of concave parabola, and chloride ion content decreases slowly along the lengthway direction of cement mortar samples in the distance of 20-80 mm from the bottom. Lots of chloride ions accumulate in cement mortar surface layer under the effect of capillary rise and evaporation and then invade cement mortar by diffusion effect. Under partial soaking condition, cement mortar is distinguished by four areas, i.e., immerging area, wet area, crystallization area and dry area.
文摘Fly ash is the most inexpensive cementitious material,and its presence in concrete has increased in recent years because it has become more durable and environmentally friendly.This study examines densified mixture concrete and the effect of fly ash quality on high-flow,high-strength concrete.Tests show that when the same mixture achieves identical flow standards(slump >250 mm;slump flow >600 mm),the fly ash quality affects the nature of the concrete;additionally,and adding Class F fly ash to concrete(loss on ignition=6%)is more workable than adding Class C fly ash(loss on ignition=3%).However,adding fly ash with a high loss on ignition(9%)to concrete requires a substantial increase in the mixing water and a dose of superplasticizer to achieve the required workability.This reduces the quality of the concrete,which subsequently deteriorates its safety and durability.
文摘This paper describes a study on the load bearing capacity of newly developed high density sintered metal gears with surface-densification. High density sintered metal gears were hobbed, and then surface-rolled. These gears were case-carburized after surface-rolling. The effect of surface-rolling on the surface property was examined by measuring porosity and hardness near surfaces of rolled gears. Running tests for these gears were performed. A failure mode and load bearing capacity of high density sintered metal gears and the effects of surface-rolling on the load bearing capacity of sintered metal gears were determined, and the results were compared with those of carburized wrought steel gears and conventional sintered metal gears. The experimental results show that the load bearing capacity of a newly developed high density sintered metal gear with surface-densification is higher than that of a carburized wrought steel gear.
