Influences of admixtures on the workability and strength of high performance concrete (HPC) are in- vestigated. The types of investigated admixtures include naphthalene series high range water reducing agent, polyca...Influences of admixtures on the workability and strength of high performance concrete (HPC) are in- vestigated. The types of investigated admixtures include naphthalene series high range water reducing agent, polycarboxlic series high range water reduce agent and sodium sulfate hardening accelerating agent. Two kinds of curing condition, namely steam curing condition and standard curing condition, are adopted. The result shows that HPC, added with polycarboxlic series of high performance water reducer, has high workability and strength, while sodium sulfate accelerating agent causes poor workability and low strength. Thus for vapor-cured HPC and its formulations, naphthalene series high range water reducing agent with less sodium sulfate should be given pri- ority. Therefore, the differences of curing conditions should be considered when selecting HPC admixtures.展开更多
The influence of glycol,the main composition of the most frequently used aircraft dicer,on the freeze-thaw durability of high performance concrete(HPC)is investigated.Freeze-thaw durability of HPC is tested by accel...The influence of glycol,the main composition of the most frequently used aircraft dicer,on the freeze-thaw durability of high performance concrete(HPC)is investigated.Freeze-thaw durability of HPC is tested by accelerated freeze-thaw test.Four kinds of the solution,i.e.,tap water,3.5% NaCl solution,glycol solutions,and a LBR-A type commercial aircraft deicer are employed.Results show that freeze-thaw durability of HPC exposed to glycol solutions is closely related to the solution concentrations.The failure of HPC exposed to 3.5% glycol solution is similar to that of those exposed to 3.5% NaCl solution,i.e.,serious surface scaling.While the damage of HPC exposed to 12.5%—25% glycol solutions is postponed.Compared with glycol solution,the commercial aircraft deicer has much more negative effects on HPC freeze-thaw durability compared with 3.5% NaCl solution.In the presence of commercial aircraft deicer for HPC subjected to freeze-thaw cycles,the deterioration is mainly due to scaling and spalling.展开更多
The impact properties of normal concrete (NC) and reinforced concrete (RC) specimens,steel fibre reinforced concrete (SFRC) specimens and RC+SFRC specimens with different steel fibre dosages were investigated with the...The impact properties of normal concrete (NC) and reinforced concrete (RC) specimens,steel fibre reinforced concrete (SFRC) specimens and RC+SFRC specimens with different steel fibre dosages were investigated with the drop-weight impact test recommended by ACI Committee 544.The results indicate that the number of blows to final failure is greatly increased by addition of steel fibres.Moreover,the combination of steel fibres and steel rebars demonstrates a significant positive composite effect on the impact resistance,which results in the improvement in impact toughness of concrete specimens.In the view of variation of impact test results,the two-parameter Weibull distribution was adopted to analyze the experimental data.It is proved that the probabilistic distributions of the blows to first crack and to final failure of six types of samples approximately follow two-parameter Weibull distribution.展开更多
The influences of water/cement ratio and admixtures on carbonation resistance of sulphoaluminate cement-based high performance concrete (HPC) were investigated. The experimental results show that with the decreasing...The influences of water/cement ratio and admixtures on carbonation resistance of sulphoaluminate cement-based high performance concrete (HPC) were investigated. The experimental results show that with the decreasing water/cement ratio, the carbonation depth of sulphoaluminate cement-based HPC is decreased remarkably, and the carbonation resistance capability is also improved with the adding admixtures. The morphologies and structure characteristics of sulphoaluminate cement hydration products before and after carbonation were analyzed using SEM and XRD. The analysis results reveal that the main hydration product of sulphoaluminate cement, that is ettringite (AFt), decomposes after carbonation.展开更多
With the modern development of chemical and mineral admixtures, it is now possible to produce much higher performance concrete than before. Higher performance does not only mean higher strength, but also better durabi...With the modern development of chemical and mineral admixtures, it is now possible to produce much higher performance concrete than before. Higher performance does not only mean higher strength, but also better durability, lower risk of thermal cracking and higher dimensional stability etc. The three most effective admixtures for producing high performance concrete are superplastieizer, pulverized fuel ash and condensed silica fume. This paper outlines the properties of these materials and presents some practical guidelines for their usage.展开更多
The relationship between compressive strength obtained by universal testing machine and rebound value obtained by the hammer of high performance concrete was systematically investigated at the macro level. And a model...The relationship between compressive strength obtained by universal testing machine and rebound value obtained by the hammer of high performance concrete was systematically investigated at the macro level. And a model of high performance concrete strength curve was established from them. At the micro level, the microstructure, hydration products and pore structure of concrete surface were analyzed by scanning electron microscopy(SEM), comprehensive thermal analysis(TG-DSC) and mercury intrusion porosimetry(MIP), respectively. The effect of carbonation on surface strength was also investigated. The results showed that the concrete surface hardness layer grew rapidly at early stage and then stabilized at last with ongoing curing age; the rebound value and compressive strength of concrete with slag were higher than those of concrete with the same content of fly ash. In addition, the strength curve obtained by the least square method can satisfy the local standard requirements with an average relative error of 8.9% and a relative standard deviation of 11.3%. When the carbonation depth was 6 mm, the compressive strength calculated by national uniform strength curve was 25 PMa higher than that by high performance concrete.展开更多
The shrinkage behavior of high performance cement concrete made from Portland cement, ultra fine granulated blast furnace slag and pulverized fly ash with addition of superplasticizer at different temperatures from am...The shrinkage behavior of high performance cement concrete made from Portland cement, ultra fine granulated blast furnace slag and pulverized fly ash with addition of superplasticizer at different temperatures from ambient temperature to 120 ℃ under different seuliug conditions was investigated by means of length change measurement on cylindrical concrete specimens along with curing age. Results show that drying shrinkage deformations of titled concrete specimens increased rapidly as the curing temperature rose. The development of dryiing shrinkage deformatian can be efficiently controlled with the aid of aluminum tape sealing as compared with the unsealed specimens, especially when the curing temperature is below 60℃ , although it will increase dramatically when the curing temperature is elevated to above 90%" . Polymer coating on concrete specimens showed a similar effect on the control of drying shrinkage as the sealing operation with aluminum tape.展开更多
With the loading test equipment of corrosion fatigue specially designed, the corrosion fatigue characteristics of high performance concrete (HPC) withstanding the interaction of third point fatigue loading and Na_2SO_...With the loading test equipment of corrosion fatigue specially designed, the corrosion fatigue characteristics of high performance concrete (HPC) withstanding the interaction of third point fatigue loading and Na_2SO_4 solution were investigated and analyzed. The experimental results indicate that water-binder ratio evidently influences the corrosion fatigue characteristics of HPC, and a moderate quantitative fine mineral admixture enhances the corrosion fatigue resistance of HPC. The effect is more significant when fly ash and silica fume are added.展开更多
The effects of green high performance concrete (GHPC) admixture on the anti-chloride permeability and anti- chloride corrodibility of concrete are studied by a series of experiments designed on the basis of the diffus...The effects of green high performance concrete (GHPC) admixture on the anti-chloride permeability and anti- chloride corrodibility of concrete are studied by a series of experiments designed on the basis of the diffusion principle and electro-chemical principle. The GHPC admixture consists of fly ash, gangue, slag, red mud, etc., of which the mass fraction of industrial residues is over 96 %. The anti-permeabilities and anti-corrodibilities of the tested GHPC and normal concrete (NC) are evaluated by the Diffusion Coefficients of chloride which was obtained by measuring the concentration of chloride in the tested systems by the voltage difference method. It is found that the adoption of GHPC admixture greatly improves the anti-chloride permeability and anti-chloride corrodibility by modifying the inner structure and contracting the porosity of concrete to the reduce considerably the diffusion rate of chloride. The admixture is desirable regarding its engineering performances as well as economical and environmental interests.展开更多
Durability design of recycled high performance concrete(RHPC) is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate(CRA). We discussed a frostdurability-based mix propo...Durability design of recycled high performance concrete(RHPC) is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate(CRA). We discussed a frostdurability-based mix proportion design method for RHPC using 100 % CRA and natural sand. Five groups of RHPC mixes with five strength grades(40, 50, 60, 70 and 80 MPa) were produced using CRA with four quality classes, and their workability, 28 d compressive strengths and frost resistances(measured by the compressive strength loss ratio and the relative dynamic modulus of elasticity) were tested. Relationships between the 28 d compressive strength, the frost resistance and the CRA quality characteristic parameter, water absorption, were then developed. The criterion of a CRA maximum water absorption limit value for RHPC was suggested, independent of its source and quality class. The results show that all RHPC mixes achieve the expected target workability, strength, and frost durability. The research results demonstrate that the application of the proposed method does not require trial testing prior to use.展开更多
C60 High Performance Concrete (HPC) was prepared by limiting cement content and adopting compositesuperplasticizer, low-alkalinity expansive agent and high-quality line mixture. The results showed that the performance...C60 High Performance Concrete (HPC) was prepared by limiting cement content and adopting compositesuperplasticizer, low-alkalinity expansive agent and high-quality line mixture. The results showed that the performance of the prepared C60 HPC was excellent. By adopting some advanced construction techniques such as usingsecondary vibration and secondary face compaction, controlling temperature difference and paying special attentionto early curing in the construction process, the prepared C60 HPC had been successfully applied in the monolithicstructure of huge building.展开更多
The fracture behaviour of three fiber reinforced and regular HPC (high performance concretes) is presented in this paper. Two mixes are based on optimization of HPC whereas the third mix was a commercial mix develop...The fracture behaviour of three fiber reinforced and regular HPC (high performance concretes) is presented in this paper. Two mixes are based on optimization of HPC whereas the third mix was a commercial mix developed by CONTEC ApS (Denmark). The wedge splitting test setup with 48 cubical specimens was used experimentally and the cracked non-linear hinge model based on the fictitious crack model was applied for the interpretation of the results. The stress-crack opening relationships were extracted by using inverse analysis algorithm for various multi-linear softening curves. This showed that the refinement of the softening curves reflects in improved accuracy of the WST (wedge splitting test) simulation in comparison with bi-linear softening curves with acceptable increase of computational time. Furthermore, the fracture mechanics parameters such as COD (crack opening displacement), fracture energy and characteristic length were experimentally determined. Experiments were performed at 1, 3, 7 and 28 days. Fracture energy, Gf, was found to increase with age, while the characteristic length, Lch, was found to decrease.展开更多
An experimental investigation was conducted to identify the characteristics of crack growth in high performance concrete (HPC) subjected to fire, including two parts of work, i.e. crack growth resistance determination...An experimental investigation was conducted to identify the characteristics of crack growth in high performance concrete (HPC) subjected to fire, including two parts of work, i.e. crack growth resistance determinations and cracking observations, using concrete of three strength grades 40 MPa, 70 MPa, and 110 MPa. The crack growth resistance curves (R-curves ) of HPC subjected to high temperatures were determined using notched three-point bend beam specimens of 100 mm×100 mm×300mm. The R-curve (crack growth resistance curve) flattening shows that the crack growth resistance has been significantly reduced by elevated temperature. Concrete with a higher strength grade has a steeper R-curve, with a higher fracture toughness but a shorter critical crack growth. The shorter critical crack growth means that concrete of a higher strength grade has a more brittle behavior. The concrete cracking observations reveal that the consequences of rapid heating are quite different from those of slow heating. For slow heating at a rate of 0.5℃/min, HPC suffered no obvious cracking below 600℃ even if it had a high moisture content. Explosive spalling is an extreme case of the internal cracking driven mainly by vapor pressure. All these results confirmed the vapor pressure mechanism for spading behavior which should be more significant for denser concrete. The crack growth ranges obtained from the R-curve determination results are in good agreement with those measured in the concrete cracking observations.展开更多
Calcine and mill kaolin were used under agreeable technological conditions to generate matakaolin (MK). The autogenous shrinkage performance of high performance concrete added with MK was researched. It is shown tha...Calcine and mill kaolin were used under agreeable technological conditions to generate matakaolin (MK). The autogenous shrinkage performance of high performance concrete added with MK was researched. It is shown that MK has an effective inhibitory action to early autogenous shrinkage of cement concrete, and the inhibitory action increases with the increase of MK. The autogenous shrinkage values from 24 hours after placement to 56 days are all higher than those of the contrasted concrete, among which, the value of the concrete with 5% MK is the highest. But the total shrinkage values in 56 days are all less than those of the contrasted test pieces. The total contraction after 24 h of placement decreases as the increase of MK, moreover, it is greatly less than that of the contrasted ones.展开更多
In order to seek the creep change rules of ased concrete with two different mix proportions, the test is carried out in the situation which is similar to that of the creation of concrete C60, and the creep test on the...In order to seek the creep change rules of ased concrete with two different mix proportions, the test is carried out in the situation which is similar to that of the creation of concrete C60, and the creep test on the concrete of two different mix proportions is done under standard lab. Based on creep test of the high performance concrete, the creep degree and the creep coefficient are obtained. By comparing with the wide-adopted models of AC1209 (1997) and CEB- FIP MC90, it is found that the test result is good at its regularity and the research results offer reference to the calculating analysis of the on-the-spot experimental data.展开更多
High performance concrete originated in the generation of high strength concrete, and it is a new high technology of concrete, is in common with high quality and in concrete. High durability on the perspective of impr...High performance concrete originated in the generation of high strength concrete, and it is a new high technology of concrete, is in common with high quality and in concrete. High durability on the perspective of improvement and become, use a lot of high quality raw materials and modern technology, is the main development direction of concrete. Because its comprehensive performance by the superiority of the focus of the society, the strict construction technology in the extensive application in the highway bridge, high performance can the use of concrete can improve the efficiency of its safety and avoid unnecessary accidents展开更多
This study intends to find out the correlation between the cover depth and the bond characteristics of UHPC through pull-out tests of UHPC specimens with different cover depths and bond tests of rebar using flexural m...This study intends to find out the correlation between the cover depth and the bond characteristics of UHPC through pull-out tests of UHPC specimens with different cover depths and bond tests of rebar using flexural members. In this experimental study, specimens are fabricated with the lap-splice length as test variable in relation with the calculation of the lap-splice length for 180- MPa UHPC. Moreover, specimens are also fabricated with the cover depth as test variable to evaluate the effect of the cover depth on the UHPC flexural members. The load-displacement curves are analyzed for each of these test variables to compute the lap-splice length proposed in the K-UHPC structural design guideline and to evaluate the influence of the cover depth on the flexural members. As a result, the stability of the structural behavior can be significantly enhanced by increasing slightly the cover depth specification of the current UHPC Structure Design Guideline from the maximum value between 1.5 times of rebar diameter and 20 mm to the maximum value between 1.5 times of rebar diameter and 25 mm.展开更多
Experimental investigation was conducted to characterize the responses of high performance concrete(HPC) subjected to multiaxial compressive stresses. The HPC specimens were prepared with three different mix proportio...Experimental investigation was conducted to characterize the responses of high performance concrete(HPC) subjected to multiaxial compressive stresses. The HPC specimens were prepared with three different mix proportions, which corresponds to three different uniaxial compressive strengths. The cubic specimens with size of 100 mm for each edge were tested with servo-hydraulic actuators at different stress ratios. The principal stresses and strains of the specimens were recorded, and the failure of the cubic specimens under various stress states was examined. The experimental results indicated that the stress states and stress ratios had significant influence on the strength and deformation of HPC under biaxial and triaxial compression, especially under triaxial compression. Failure criteria were proposed for the HPC specimens under biaxial and triaxial compressive loading. The test results provided a valuable reference for obtaining multi-axial constitutive law for HPC.展开更多
The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5% , 10% and 20% metakaolin were prepared at a water / cementitious ...The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5% , 10% and 20% metakaolin were prepared at a water / cementitious material ratio ( W/C) of 0. 30. In parallel, concrete mixtures with the replacement of cement by 20% fly ash or 5 and 10% silica fume were prepared for comparison. The specimens were cured in water at 27℃ for 3 to 90 days. The results show that at the early age of curing (3 days and 7 days), metakaolin replacements increase the compressive strength, but silica fume replacement slightly reduces the compressive strength. At the age of and after 28 days , the compressive strength of the concrete with metakaolin and silica fume replacement increases. A strong reduction in the total porosity and average pore diameter were observed in the concrete with MK 20% and 10% in the first 7 days.展开更多
Ordinary concrete presents short service life when used for building and repairing high-grade road with heavy traffic due to its large brittleness, poor bending flexibility and serious shrinkage on drying. In this pap...Ordinary concrete presents short service life when used for building and repairing high-grade road with heavy traffic due to its large brittleness, poor bending flexibility and serious shrinkage on drying. In this paper, a new kind of high performance concrete has been designed by means of combination of organic, inorganic material as well as metal material. The research and application have shown that this new concrete can significantly counteract the deficiency of ordinary concrete and give excellent mechanical properties and pavement performances. The application of this new kind of concrete is of great social and economic significance.展开更多
基金Supported by the National Basic Research Programe of China("973"Program)(2009CB623203)the Construction Department of Zhejiang Province Foundation(1006)+1 种基金the Education Department of Zhejiang Province Foundation(Y200909029)the Doctoral Innovation Foundation of Nanjing University of Aeronautics andAstronautics(BCXJ07-04)~~
文摘Influences of admixtures on the workability and strength of high performance concrete (HPC) are in- vestigated. The types of investigated admixtures include naphthalene series high range water reducing agent, polycarboxlic series high range water reduce agent and sodium sulfate hardening accelerating agent. Two kinds of curing condition, namely steam curing condition and standard curing condition, are adopted. The result shows that HPC, added with polycarboxlic series of high performance water reducer, has high workability and strength, while sodium sulfate accelerating agent causes poor workability and low strength. Thus for vapor-cured HPC and its formulations, naphthalene series high range water reducing agent with less sodium sulfate should be given pri- ority. Therefore, the differences of curing conditions should be considered when selecting HPC admixtures.
基金Supported by the National Basic Research Program of China("973"Program)(2009CB623203)the China Postdoctoral Science Foundation(20070421036)+1 种基金the Natural Science Foundation of Jiangsu Province(BK2005216)the Research Foundation of Nanjing University of Aeronautics and Astronautics(NS2010015)~~
文摘The influence of glycol,the main composition of the most frequently used aircraft dicer,on the freeze-thaw durability of high performance concrete(HPC)is investigated.Freeze-thaw durability of HPC is tested by accelerated freeze-thaw test.Four kinds of the solution,i.e.,tap water,3.5% NaCl solution,glycol solutions,and a LBR-A type commercial aircraft deicer are employed.Results show that freeze-thaw durability of HPC exposed to glycol solutions is closely related to the solution concentrations.The failure of HPC exposed to 3.5% glycol solution is similar to that of those exposed to 3.5% NaCl solution,i.e.,serious surface scaling.While the damage of HPC exposed to 12.5%—25% glycol solutions is postponed.Compared with glycol solution,the commercial aircraft deicer has much more negative effects on HPC freeze-thaw durability compared with 3.5% NaCl solution.In the presence of commercial aircraft deicer for HPC subjected to freeze-thaw cycles,the deterioration is mainly due to scaling and spalling.
基金Project(50578026) supported by the National Natural Science Foundation of ChinaProject supported by FCT (SFRH/BPD/22680/2005)and Research Center of Mathematics of the University of Minho through the FCT Pluriannual Funding Program
文摘The impact properties of normal concrete (NC) and reinforced concrete (RC) specimens,steel fibre reinforced concrete (SFRC) specimens and RC+SFRC specimens with different steel fibre dosages were investigated with the drop-weight impact test recommended by ACI Committee 544.The results indicate that the number of blows to final failure is greatly increased by addition of steel fibres.Moreover,the combination of steel fibres and steel rebars demonstrates a significant positive composite effect on the impact resistance,which results in the improvement in impact toughness of concrete specimens.In the view of variation of impact test results,the two-parameter Weibull distribution was adopted to analyze the experimental data.It is proved that the probabilistic distributions of the blows to first crack and to final failure of six types of samples approximately follow two-parameter Weibull distribution.
基金Funded by the National Natural Science Foundation of China(No.50872043)
文摘The influences of water/cement ratio and admixtures on carbonation resistance of sulphoaluminate cement-based high performance concrete (HPC) were investigated. The experimental results show that with the decreasing water/cement ratio, the carbonation depth of sulphoaluminate cement-based HPC is decreased remarkably, and the carbonation resistance capability is also improved with the adding admixtures. The morphologies and structure characteristics of sulphoaluminate cement hydration products before and after carbonation were analyzed using SEM and XRD. The analysis results reveal that the main hydration product of sulphoaluminate cement, that is ettringite (AFt), decomposes after carbonation.
文摘With the modern development of chemical and mineral admixtures, it is now possible to produce much higher performance concrete than before. Higher performance does not only mean higher strength, but also better durability, lower risk of thermal cracking and higher dimensional stability etc. The three most effective admixtures for producing high performance concrete are superplastieizer, pulverized fuel ash and condensed silica fume. This paper outlines the properties of these materials and presents some practical guidelines for their usage.
基金Funded by the National Natural Science Foundation of China(No.2015CB655102)National Science&Technology Pillar Program(No.2014BAB15B01-02)
文摘The relationship between compressive strength obtained by universal testing machine and rebound value obtained by the hammer of high performance concrete was systematically investigated at the macro level. And a model of high performance concrete strength curve was established from them. At the micro level, the microstructure, hydration products and pore structure of concrete surface were analyzed by scanning electron microscopy(SEM), comprehensive thermal analysis(TG-DSC) and mercury intrusion porosimetry(MIP), respectively. The effect of carbonation on surface strength was also investigated. The results showed that the concrete surface hardness layer grew rapidly at early stage and then stabilized at last with ongoing curing age; the rebound value and compressive strength of concrete with slag were higher than those of concrete with the same content of fly ash. In addition, the strength curve obtained by the least square method can satisfy the local standard requirements with an average relative error of 8.9% and a relative standard deviation of 11.3%. When the carbonation depth was 6 mm, the compressive strength calculated by national uniform strength curve was 25 PMa higher than that by high performance concrete.
文摘The shrinkage behavior of high performance cement concrete made from Portland cement, ultra fine granulated blast furnace slag and pulverized fly ash with addition of superplasticizer at different temperatures from ambient temperature to 120 ℃ under different seuliug conditions was investigated by means of length change measurement on cylindrical concrete specimens along with curing age. Results show that drying shrinkage deformations of titled concrete specimens increased rapidly as the curing temperature rose. The development of dryiing shrinkage deformatian can be efficiently controlled with the aid of aluminum tape sealing as compared with the unsealed specimens, especially when the curing temperature is below 60℃ , although it will increase dramatically when the curing temperature is elevated to above 90%" . Polymer coating on concrete specimens showed a similar effect on the control of drying shrinkage as the sealing operation with aluminum tape.
文摘With the loading test equipment of corrosion fatigue specially designed, the corrosion fatigue characteristics of high performance concrete (HPC) withstanding the interaction of third point fatigue loading and Na_2SO_4 solution were investigated and analyzed. The experimental results indicate that water-binder ratio evidently influences the corrosion fatigue characteristics of HPC, and a moderate quantitative fine mineral admixture enhances the corrosion fatigue resistance of HPC. The effect is more significant when fly ash and silica fume are added.
文摘The effects of green high performance concrete (GHPC) admixture on the anti-chloride permeability and anti- chloride corrodibility of concrete are studied by a series of experiments designed on the basis of the diffusion principle and electro-chemical principle. The GHPC admixture consists of fly ash, gangue, slag, red mud, etc., of which the mass fraction of industrial residues is over 96 %. The anti-permeabilities and anti-corrodibilities of the tested GHPC and normal concrete (NC) are evaluated by the Diffusion Coefficients of chloride which was obtained by measuring the concentration of chloride in the tested systems by the voltage difference method. It is found that the adoption of GHPC admixture greatly improves the anti-chloride permeability and anti-chloride corrodibility by modifying the inner structure and contracting the porosity of concrete to the reduce considerably the diffusion rate of chloride. The admixture is desirable regarding its engineering performances as well as economical and environmental interests.
基金Funded by the National Natural Science Foundation of China(No.51278073)Prospective Joint Research Project of Jiangsu Province(No.BY2015027-23)State Key Laboratory for Geo Mechanics and Deep Underground Engineering,China University of Mining&Technology(No.SKLGDUEK1704)
文摘Durability design of recycled high performance concrete(RHPC) is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate(CRA). We discussed a frostdurability-based mix proportion design method for RHPC using 100 % CRA and natural sand. Five groups of RHPC mixes with five strength grades(40, 50, 60, 70 and 80 MPa) were produced using CRA with four quality classes, and their workability, 28 d compressive strengths and frost resistances(measured by the compressive strength loss ratio and the relative dynamic modulus of elasticity) were tested. Relationships between the 28 d compressive strength, the frost resistance and the CRA quality characteristic parameter, water absorption, were then developed. The criterion of a CRA maximum water absorption limit value for RHPC was suggested, independent of its source and quality class. The results show that all RHPC mixes achieve the expected target workability, strength, and frost durability. The research results demonstrate that the application of the proposed method does not require trial testing prior to use.
文摘C60 High Performance Concrete (HPC) was prepared by limiting cement content and adopting compositesuperplasticizer, low-alkalinity expansive agent and high-quality line mixture. The results showed that the performance of the prepared C60 HPC was excellent. By adopting some advanced construction techniques such as usingsecondary vibration and secondary face compaction, controlling temperature difference and paying special attentionto early curing in the construction process, the prepared C60 HPC had been successfully applied in the monolithicstructure of huge building.
文摘The fracture behaviour of three fiber reinforced and regular HPC (high performance concretes) is presented in this paper. Two mixes are based on optimization of HPC whereas the third mix was a commercial mix developed by CONTEC ApS (Denmark). The wedge splitting test setup with 48 cubical specimens was used experimentally and the cracked non-linear hinge model based on the fictitious crack model was applied for the interpretation of the results. The stress-crack opening relationships were extracted by using inverse analysis algorithm for various multi-linear softening curves. This showed that the refinement of the softening curves reflects in improved accuracy of the WST (wedge splitting test) simulation in comparison with bi-linear softening curves with acceptable increase of computational time. Furthermore, the fracture mechanics parameters such as COD (crack opening displacement), fracture energy and characteristic length were experimentally determined. Experiments were performed at 1, 3, 7 and 28 days. Fracture energy, Gf, was found to increase with age, while the characteristic length, Lch, was found to decrease.
基金The authors gratefully acknowledge the financial support of both the National Natural Science Foundation of China(project No.50108001)the Pandeng Foundation Project of Beijing Jiao Tong University.
文摘An experimental investigation was conducted to identify the characteristics of crack growth in high performance concrete (HPC) subjected to fire, including two parts of work, i.e. crack growth resistance determinations and cracking observations, using concrete of three strength grades 40 MPa, 70 MPa, and 110 MPa. The crack growth resistance curves (R-curves ) of HPC subjected to high temperatures were determined using notched three-point bend beam specimens of 100 mm×100 mm×300mm. The R-curve (crack growth resistance curve) flattening shows that the crack growth resistance has been significantly reduced by elevated temperature. Concrete with a higher strength grade has a steeper R-curve, with a higher fracture toughness but a shorter critical crack growth. The shorter critical crack growth means that concrete of a higher strength grade has a more brittle behavior. The concrete cracking observations reveal that the consequences of rapid heating are quite different from those of slow heating. For slow heating at a rate of 0.5℃/min, HPC suffered no obvious cracking below 600℃ even if it had a high moisture content. Explosive spalling is an extreme case of the internal cracking driven mainly by vapor pressure. All these results confirmed the vapor pressure mechanism for spading behavior which should be more significant for denser concrete. The crack growth ranges obtained from the R-curve determination results are in good agreement with those measured in the concrete cracking observations.
文摘Calcine and mill kaolin were used under agreeable technological conditions to generate matakaolin (MK). The autogenous shrinkage performance of high performance concrete added with MK was researched. It is shown that MK has an effective inhibitory action to early autogenous shrinkage of cement concrete, and the inhibitory action increases with the increase of MK. The autogenous shrinkage values from 24 hours after placement to 56 days are all higher than those of the contrasted concrete, among which, the value of the concrete with 5% MK is the highest. But the total shrinkage values in 56 days are all less than those of the contrasted test pieces. The total contraction after 24 h of placement decreases as the increase of MK, moreover, it is greatly less than that of the contrasted ones.
文摘In order to seek the creep change rules of ased concrete with two different mix proportions, the test is carried out in the situation which is similar to that of the creation of concrete C60, and the creep test on the concrete of two different mix proportions is done under standard lab. Based on creep test of the high performance concrete, the creep degree and the creep coefficient are obtained. By comparing with the wide-adopted models of AC1209 (1997) and CEB- FIP MC90, it is found that the test result is good at its regularity and the research results offer reference to the calculating analysis of the on-the-spot experimental data.
文摘High performance concrete originated in the generation of high strength concrete, and it is a new high technology of concrete, is in common with high quality and in concrete. High durability on the perspective of improvement and become, use a lot of high quality raw materials and modern technology, is the main development direction of concrete. Because its comprehensive performance by the superiority of the focus of the society, the strict construction technology in the extensive application in the highway bridge, high performance can the use of concrete can improve the efficiency of its safety and avoid unnecessary accidents
文摘This study intends to find out the correlation between the cover depth and the bond characteristics of UHPC through pull-out tests of UHPC specimens with different cover depths and bond tests of rebar using flexural members. In this experimental study, specimens are fabricated with the lap-splice length as test variable in relation with the calculation of the lap-splice length for 180- MPa UHPC. Moreover, specimens are also fabricated with the cover depth as test variable to evaluate the effect of the cover depth on the UHPC flexural members. The load-displacement curves are analyzed for each of these test variables to compute the lap-splice length proposed in the K-UHPC structural design guideline and to evaluate the influence of the cover depth on the flexural members. As a result, the stability of the structural behavior can be significantly enhanced by increasing slightly the cover depth specification of the current UHPC Structure Design Guideline from the maximum value between 1.5 times of rebar diameter and 20 mm to the maximum value between 1.5 times of rebar diameter and 25 mm.
基金supported by the National Natural Science Foundation of China(Grant No.51278118)the National Basic Research Program of China("973"Project)(Grant No.2009CB623200)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Experimental investigation was conducted to characterize the responses of high performance concrete(HPC) subjected to multiaxial compressive stresses. The HPC specimens were prepared with three different mix proportions, which corresponds to three different uniaxial compressive strengths. The cubic specimens with size of 100 mm for each edge were tested with servo-hydraulic actuators at different stress ratios. The principal stresses and strains of the specimens were recorded, and the failure of the cubic specimens under various stress states was examined. The experimental results indicated that the stress states and stress ratios had significant influence on the strength and deformation of HPC under biaxial and triaxial compression, especially under triaxial compression. Failure criteria were proposed for the HPC specimens under biaxial and triaxial compressive loading. The test results provided a valuable reference for obtaining multi-axial constitutive law for HPC.
基金Funded by the Research Grants Council of the Hong Kong SAR Government Project(31.37. A212)
文摘The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5% , 10% and 20% metakaolin were prepared at a water / cementitious material ratio ( W/C) of 0. 30. In parallel, concrete mixtures with the replacement of cement by 20% fly ash or 5 and 10% silica fume were prepared for comparison. The specimens were cured in water at 27℃ for 3 to 90 days. The results show that at the early age of curing (3 days and 7 days), metakaolin replacements increase the compressive strength, but silica fume replacement slightly reduces the compressive strength. At the age of and after 28 days , the compressive strength of the concrete with metakaolin and silica fume replacement increases. A strong reduction in the total porosity and average pore diameter were observed in the concrete with MK 20% and 10% in the first 7 days.
文摘Ordinary concrete presents short service life when used for building and repairing high-grade road with heavy traffic due to its large brittleness, poor bending flexibility and serious shrinkage on drying. In this paper, a new kind of high performance concrete has been designed by means of combination of organic, inorganic material as well as metal material. The research and application have shown that this new concrete can significantly counteract the deficiency of ordinary concrete and give excellent mechanical properties and pavement performances. The application of this new kind of concrete is of great social and economic significance.