Service life of reinforced concrete structures usually was designed on the basis of one selected deteriorating mechanism as for instance carbonation,chloride penetration,and frost action.It could be shown in the meant...Service life of reinforced concrete structures usually was designed on the basis of one selected deteriorating mechanism as for instance carbonation,chloride penetration,and frost action.It could be shown in the meantime by numerous authors,however,that combined actions such as chloride penetration under mechanical load or chloride penetration in combination with freeze-thaw cycles may shorten the service life of reinforced concrete structures more than individual processes acting alone.We have found that chloride penetration is accelerated significantly by freeze-thaw cycles.Frost damage not only reduces mechanical strength and elastic modulus but migration of chloride is facilitated in the damaged pore structure.Chloride penetration can be retarded by the addition of silane emulsion to the fresh concrete.In this way Integral Water Repellent Concrete（IWRC） can be produced.Migration of water and ions dissolved in water can not be prevented by integral water repellent treatment but it is slowed down.The combination of damage mechanisms and the protective measures by integral water repellent treatment have to be taken into consideration in realistic service life prediction and design.展开更多
The recently-developed boundary effect concept and the associated asymptotic model are used to analyze size-dependent fracture of concrete specimens.It is shown that the dependence of concrete fracture on specimen siz...The recently-developed boundary effect concept and the associated asymptotic model are used to analyze size-dependent fracture of concrete specimens.It is shown that the dependence of concrete fracture on specimen size,crack and/or ligament length is due to the same mechanism,i.e.the interactions between the crack tip fracture process zone and specimen's boundaries.By introducing an equivalent crack length ae,dimension dependent fracture becomes equivalent to fracture of a large plate with a small edge crack,and therefore,follows the same relationship of the 'net' nominal strength σn versus ae.As a result,the size dependent fracture can be predicted using the data measured on different types of specimens.To demonstrate the flexibility and effectiveness of the asymptotic boundary effect model,previously published results of three test series are analyzed.Excellent agreement has been found.Implications of the successful prediction are discussed.展开更多
Chloride content and the pH value of the pore solution in the neighborhood of steel reinforcement are decisive pa- rameters for initiation and rate of corrosion. The pore solution of cement mortar and hardened cement ...Chloride content and the pH value of the pore solution in the neighborhood of steel reinforcement are decisive pa- rameters for initiation and rate of corrosion. The pore solution of cement mortar and hardened cement paste has been expressed from the pore space by high pressure in the investigation. The influence of the water-cement ratio, age, and addition of chloride to the fresh mix on chloride content in the pore solution has been determined by ion chromatography. At the same time the pH value of the pore solution has been determined. The dissolved chloride content decreases with increase in the water-cement ratio. The amount of bound chloride increases with time, but it decreases with decreasing content of dissolved chloride in the pore solution. A significant influence of carbonation on the dissolved chloride content of the pore solution has been observed. With complete carbonation, the dissolved chloride content in cement mortar and hardened cement paste increases by a factor between 2 and 12. The bound chloride decreases by 27%--54%. As expected, the pH value decreases from around 13.2 to as low as 8.0 due to car- bonation. It can be concluded that carbonation not only lowers the pH value but liberates bound chloride. This is one obvious reason why the combined action of chloride penetration and carbonation accelerates steel corrosion and shortens the service life of reinforced concrete structures.展开更多
基金Funded by the National Natural Science Foundation of China(51438007)the National Basic Research Program of China(973 Program)(2009CB623203)
文摘Service life of reinforced concrete structures usually was designed on the basis of one selected deteriorating mechanism as for instance carbonation,chloride penetration,and frost action.It could be shown in the meantime by numerous authors,however,that combined actions such as chloride penetration under mechanical load or chloride penetration in combination with freeze-thaw cycles may shorten the service life of reinforced concrete structures more than individual processes acting alone.We have found that chloride penetration is accelerated significantly by freeze-thaw cycles.Frost damage not only reduces mechanical strength and elastic modulus but migration of chloride is facilitated in the damaged pore structure.Chloride penetration can be retarded by the addition of silane emulsion to the fresh concrete.In this way Integral Water Repellent Concrete（IWRC） can be produced.Migration of water and ions dissolved in water can not be prevented by integral water repellent treatment but it is slowed down.The combination of damage mechanisms and the protective measures by integral water repellent treatment have to be taken into consideration in realistic service life prediction and design.
基金Supported by the Australian Research Council(ARC)under the scheme of Discovery GrantNational Natural Scienc Foundation of China(50739001)Research Fund for the Doctoral Programof Higher Education(20070429001)
文摘The recently-developed boundary effect concept and the associated asymptotic model are used to analyze size-dependent fracture of concrete specimens.It is shown that the dependence of concrete fracture on specimen size,crack and/or ligament length is due to the same mechanism,i.e.the interactions between the crack tip fracture process zone and specimen's boundaries.By introducing an equivalent crack length ae,dimension dependent fracture becomes equivalent to fracture of a large plate with a small edge crack,and therefore,follows the same relationship of the 'net' nominal strength σn versus ae.As a result,the size dependent fracture can be predicted using the data measured on different types of specimens.To demonstrate the flexibility and effectiveness of the asymptotic boundary effect model,previously published results of three test series are analyzed.Excellent agreement has been found.Implications of the successful prediction are discussed.
基金Project supported by the Basic Research Program(973)of China(No.2009CB623230)the Natural Science Foundation of Shan-dong Province,China(No.ZR2011EEQ031)
文摘Chloride content and the pH value of the pore solution in the neighborhood of steel reinforcement are decisive pa- rameters for initiation and rate of corrosion. The pore solution of cement mortar and hardened cement paste has been expressed from the pore space by high pressure in the investigation. The influence of the water-cement ratio, age, and addition of chloride to the fresh mix on chloride content in the pore solution has been determined by ion chromatography. At the same time the pH value of the pore solution has been determined. The dissolved chloride content decreases with increase in the water-cement ratio. The amount of bound chloride increases with time, but it decreases with decreasing content of dissolved chloride in the pore solution. A significant influence of carbonation on the dissolved chloride content of the pore solution has been observed. With complete carbonation, the dissolved chloride content in cement mortar and hardened cement paste increases by a factor between 2 and 12. The bound chloride decreases by 27%--54%. As expected, the pH value decreases from around 13.2 to as low as 8.0 due to car- bonation. It can be concluded that carbonation not only lowers the pH value but liberates bound chloride. This is one obvious reason why the combined action of chloride penetration and carbonation accelerates steel corrosion and shortens the service life of reinforced concrete structures.
