EFFECTS OF REINFORCEMENT AND COARSE AGGREGATESON CHLORIDE INGRESS. INTO CONCRETE AND TIME-TO-CORROSION:Part I – Spatial Chloride Distribution and Implications

摘要

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 Cl~- migration posed 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 to outdoor conditions while cyclically ponded with a NaCl solution. Subsequent to corrosion initiation, selected slabs were cored, dissected, and [Cl~-] determined both from the cores and from shallow millings of concrete immediate to the reinforcement. It is demonstrated 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 this parameter upon such sampling. The results are discussed within the context of understanding factors that effect measured values for [Cl~-] and the relatively wide variation in [Cl~-]_(th) that has been reported in the literature.