Page 154 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

132 CORROSION CAUSES

Figure 3.2 Example of deteriorating bridge element (7).

documented (8, 9). It was shown that concrete mix design has a significant
effect on the corrosion of rebar.

The uneven distribution of chloride ions in the concrete and at the steel surface
also greatly affects the corrosion. The high level of chloride on the top layer and
decreasing chloride concentration with distance results in increased corrosion rate
because of macrocell corrosion.
Corrosion of steel in concrete is a very complex phenomenon. Although significant
research on modeling in the corrosion processes of steel in concrete has been per-
formed, accurate life prediction for concrete structures is difficult.
Nonmarine corrosion-related reinforced concrete bridge failures became a grow-
ing problem beginning in the 1960s in the “snow belt” regions following increased
usage of deicing salts. In the worst cases, bridges began to require maintenance after
a service life of 5–10 years, with the average maintenance interval being around
15 years. The quality of concrete used in bridge construction was of improved
quality in the 1970s and 1980s. This together with increased thickness and the
epoxy coated rebar led to increased service lives. New bridge structures built and
maintained with high performance, greater cover thickness, corrosion-resistant rebar,
corrosion-inhibiting admixtures, overlays, sealants, and improved CP are expected to