Chloride diffusivity of concrete cracked in flexure

Abstract

It has been recognized that corrosion of steel in cracked concrete is affected by both the surface crack width and the concrete cover thickness. The crack width/cover ratio ( W cr/ C) can be a suitable parameter to consider in relation to the durability performance of a cracked reinforced concrete. A linear relationship was observed when plotting the chloride threshold level against C/ W cr. It appears that the threshold level can be related to W cr/ C by a hyperbolic relationship. The effect of W cr/ C on the chloride threshold level appears to be more pronounced as this ratio is decreased. The Australian Standard, AS 3600, does not give any guidance on the allowable crack width at serviceability for reinforced concrete structures, except for the ‘deemed to comply’ rules. From the viewpoint of durability, a crack width limitation in AS 3600 is necessary in addition to the cover thickness, to minimize W cr/ C. Using W cr/ C=0.01, in this study, the effect of tensile steel area on the chloride diffusivity in the tension and compression zones of concrete cracked in flexure was investigated. The apparent chloride diffusion coefficient ( D a) in the tension zone was found to be higher than in the compression zone. When the tensile steel area was doubled, a significant decrease in the D a of the compression zone was observed. This could be attributed to the reduction in the porosity of the concrete in compression, which impedes diffusion process. In contrast, a marginal increase in the D a of the tension zone was observed.