Effects of Reinforcement and Coarse Aggregates on Chloride Ingress into Concrete and Time-to-Corrosion: Part 2—Spatial Distribution of Coarse Aggregates Available to Purchase

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 sodium chloride (NaCl) solution. Subsequent to corrosion initiation, selected slabs were cored, dissected, and [Cl⁻] was determined 1) within the cores and 2) from shallow millings immediate to the reinforcement, both removed from and at the active corrosion site. It is demonstrated from previous research that, in addition to the reinforcement obstruction effect, the spatial arrangement 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 distribution along the Cl⁻ diffusion path within the concrete cover were determined. 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.