Study Of Effect Of Stresses On The Fracture Behavior And Corrosion Of Prestressing Steel Wires

Prestressing steel wires(steel strands) are widely used in prestressed concrete structures. In this paper, the effects of stresses (including applied stresses and residual stresses) on the fracture behavior and corrosion of prestressing steel wires are investigated by numerical calculation and experimental method. The main contents are listed as follows:1.The effect of residual stresses on the fracture behavior of cracked prestressing steel wiresResidual stresses,generated by cold-drawn operations in prestressing steel wires,may have detrimental effects on the fracture behavior of the prestressing steel wires. Using finite element analysis,micromechanical models of fracture initiation and J-Q theory,this paper focuses on the qualitative effect of the longitudinal residual stresses on the fracture behavior of cracked prestressing steel wires,and the results have been compared with those obtained from the steel wires without residual stresses. It has been concluded that the tensile residual stresses can reduce the fracture toughness of prestressing steel wires by altering crack-tip constraint.2.The effect of applied stresses on the critical chloride concentrations of prestressing steel wiresOn the one hand,the presence of sufficient chloride ions in concrete causes breakdown of the passive films on the steel surface and leads to corrosion of the steel,on the other hand,when the applied stress exceeds the elastic limit,the plastic deformation of the prestressing steel wire is produced. To evaluate the effect of the plastic deformation on the critical chloride concentration of prestressing steel wires,the pit nucleation potential of the prestressing steel wire has been investigated by galvanostatic polarization technique as accelerated experiment method in saturated Ca(OH)₂ solutions. The experimental results indicated that,when the stress exceeds the elastic limit,the critical chloride concentration of prestressing steel wires is lower than that when the stress is within the elastic limit. This could be attributed to the plastic deformation decreased the electrode potential of prestressing steel wires, which can affect the formation of passive films in the alkaline environment, and enhanced the pitting corrosion susceptibility.3 . The effect of applied stresses on the hydrogen embrittlement susceptibility of prestressing steel wiresHydrogen embrittlement is one of the main corrosion forms of prestressing steel wires,and the stress level in prestressing steel wires has a direct effect on hydrogen embrittlement susceptibility. Coupled diffusion elastic-plastic finite element analysis was implemented in order to obtain the hydrogen concentration distribution in the notched prestressing steel wire under plane strain conditions. The results showed that applied stress has an effect on the hydrogen concentration distribution,and the applied stress has a"critical value". When the applied stress exceeds this value,the hydrogen concentration in the prestressing steel wire will sharply increase following the stress.