Abstract
Corrosion of the steel reinforcement is considered as one of the major factors for the durability of the steel reinforced concrete(RC)elements[1,2],which challenges the serviceability and loadbearing capacity of the RC structures seriously[2].It was reported that the wind could carry the chloride ions into the area as far as 3 km away from the sea[3].The chloride ions will penetrate into the concrete gradually with the exposure period elapse inevitably.Depassivation happens to the steel reinforcement gradually,and then followed by the corrosion of the steel reinforcement[4].As the volume of the corrosion products is about 2～6 times larger than that of the original steel[5],the corrosion products would result in the volumetric expansive stress to the concrete cover.Cracking would happen inevitably[6].So it will very interesting to investigate the cracking propagation of the concrete cover induced by the chloride-induced corrosion of the steel reinforcement.
In this paper,the cracking path of the concrete cover induced by the nonuniform corrosion of the steel reinforcement will be studied.A typical model of nonuniform corrosion will be involved.The Timoshenko[7]theory will be adopted according to the hypothesis of elastic behavior of thick-walled cylinder.A new analytical model to predict the propagation of the cracking pattern of the concrete cover induced by the corrosion will be proposed.
Figure 1 Melchers&Val's model
The typical corrosion morphology of Melchers& Val's model was adopted in this investigation.Figure 1 shows the cross-sectional image of the typical corroded steel reinforcement with the corrosion age of 26 years,and the Melchers&Val's model is also included so as to make the comparison.As shown in Figure 1,the pitting corrosion(nonuniform corrosion)is assumed to occur on the surface of the steel reinforcement,which was original from the top edge of the steel reinforcement.The crosssectional loss of the pitting corrosion could be calculated as follow:
where r0 is the radius of the origin steel reinforcement;Ars is the sectional loss of the pitting corrosion;p(t)is the maximum depth of the pitting corrosion.
According to Zhao et al.[8],the layer of concrete filled with the corrosion products developed with the corrosion propagation of the steel reinforcement in a linear way.The depth of concrete filled with corrosion products was marked as shown in Figure 2.The corrosion layer was marked as DCL and the depth of the concrete with the pores filled with the corrosion products was marked as DCF.
Figure 2 Three stages of the corrosion-induced cracks
The stress
contributed by the concrete cover with corrosion-induced crack can be deduced.
During the different cracking process,the corrosion pressure pcorr corresponding to the corrosion zone could be evaluated according to Timoshenko.In the hypothesis of elastic behavior of the cylinder and neglecting the Poisson effects,the pressure of a thick-walled cylinder subjected to an internal radial pressure could be deduced.