Abstract
The chloride concentration in concrete required to compromise reinforcing steel passivity and initiate active corrosion, [Cl−]th, is an important service life determinant for reinforced concrete structures. However, consensus regarding a value for [Cl−]th is lacking, as evidenced by the fact that reported experimental determinations vary by more than an order of magnitude. A recently recognized factor that contributes to the range in [Cl−]th is the obstruction to migration afforded by reinforcement, such that ingress of this species must be treated as two-rather than one-dimensional. In the present research, reinforced concrete slabs were exposed outdoors while cyclically ponded with a NaCl solution. Subsequent to corrosion initiation, selected slabs were cored, dissected, and [Cl−] determined 1) within the cores and 2) from shallow millings immediate to the reinforcement, both removed from and at the active corrosion site. It was demonstrated from previous research that, in addition to the reinforcement obstruction effect, the spatial distribution of coarse aggregates immediate to the reinforcement influences Cl− distribution and the measured value for concentration of this species. In this research, both [Cl−] and coarse aggregate distributions along the Cl− diffusion path within the concrete cover were analyzed. The results are discussed within the context of understanding factors that affect Cl− transport and the relatively wide variation in [Cl−]th that has been reported in the literature.
