Abstract
Corrosion of steel reinforcement bars in concrete could lead to critical damage to concrete structure durability,possibly even lead to structure failure[1].In practice,reinforced concrete structures in coastal areas,such as bridges and ports,inevitably experience variable mechanical loads and chloride penetration.Different kinds of loads may have an impact on the depassivation and corrosion processes in metals.Some researchers have conducted studies with respect to the influence of stress on the corrosion behavior of dif ferent metals.It is found that stress could af fect the corrosion speed of metals regardless of the environment[2-5].However,only a few studies were done in a concrete environment[6,7],and these studies merely presented qualitative conclusions.The influence mechanism of stress on steel corrosion has not been studied well.Besides,reinforcing steel bars embedded in concrete are always intersected with each other to form rebar mesh.The macro-cell corrosion between dissimilar crossed steel bars has not been well studied before.
Therefore,the present study aims to investigate the influence of tensile stress on corrosion behavior of single steel bar and macro-cell corrosion between dissimilar crossed steel bars.
In this study,the specimens were divided into two groups.In Group 1,each specimen was pre-stressed and immersed into simulated concrete pore solution within chloride ions alone,as shown in Figure 1.
Figure 1 Group 1 specimens
In Group 2,each prestressed hotrolled ribbed bar was connected with an unstressed hot-rolled plain steel bar to simulated the macro-cell corrosion between dissimilar crossed steel bars in concrete structures,as shown in Figure 2.The details of specimens are shown in Table 1.
Based on the principle of electrochemical corrosion,the polarization equation of a single steel bar for Group 1 can be expressed as Eq.(1).
where Ecorr is the self-corrosion potential,icorr is the self-corrosion current density,iL is the limit current density,βa andβc are anodic Tafel slope and cathode Tafel slope.
Figure 2 Group 2 specimens
Table 1 The details of the specimens
Considering the macro-cell corrosion between dissimilar steel bars,the polarization equation of the specimens in Group 2 can be expressed as Eq.(2).
where ia1 and ic1 are the current density of anodic reaction and cathode reaction of the hot-rolled steel bar,respectively.Ig is the macro-cell corrosion current.S1 is the surface area of the anodic steel bar.
Several electrochemical measurements were performed on the specimens to get the polarization curve and other data.Based on Eq.(1)and Eq.(2),Matlab was used to fit the data.
Results indicate that steel specimens immersed in chloride-contaminated solution under tensile loadings corroded more rapidly compared with the unstressed specimen.When the stress level gets higher,the corrosion current density gets bigger.Besides,the stress level has a great impact on macro-cell corrosion between dissimilar steel bars.The value of the macro-cell corrosion current changes with the stress level.