Remedial Measures for Reinforced Concrete Structures

The increased volume of corrosion products compared to steel can cause cracking and spalling of the surrounding concrete. Photo by Getty Images.

The high-pH (alkaline) environment of new concrete passivate the surfaces of carbon steel reinforcing elements (rebar), stifling corrosion after the formation of a thin, stable oxide layer. Over time, aggressive ions, principally chlorides from the external environment or deicing salts, diffuse through the pores of the concrete.

When a sufficient concentration of aggressive ions are present next to the reinforcement, the stable oxide layer becomes unstable and the rebar will corrode. The loss of metal can reduce the load-bearing strength of the structure. In addition, the increased volume of corrosion products compared to steel can cause cracking and spalling of the surrounding concrete.

A number of fundamental measures can be taken to address the problem of reinforcing steel corrosion. However, an important distinction has to be made in the applicability of remedial measures to new versus existing structures.

Unfortunately, the options in the following list of remedial measures are more limited for fixing existing, aging structures than for designing new constructions:

• Repairing the damaged concrete;
• Modifying the external environment—for example, choosing a different deicing agent or changing deicing salt practices (however, this will not remove salt already in the concrete);
• Modifying the internal concrete environment; for example, realkalization of concrete, chloride extraction, addition of corrosion inhibitors, etc.;
• Modifying the concrete formulation to reduce its porosity;
• Creating a barrier between the concrete and the external environment;
• Creating a barrier between the rebar steel and the internal concrete environment; for example, epoxy coating or galvanizing;
• Applying cathodic protection to the rebar structure; this also tends to migrate chlorides away from the steel (cathode) surfaces;
• Alternative, more corrosion-resistant rebar materials; such as, stainless steel;
• Alternative methods/materials of reinforcement—for example, fiber-reinforced polymer composites.

For new structures, it is believed that much progress will be made toward effective corrosion control as life-cycle strategies are implemented, as opposed to making decisions on the basis of initial capital-cost outlay alone.

With such a vision, investing in more corrosion resistant materials could prove to be a cost-effective alternative even if it significantly increases the initial cost of the structure. These costs can be offset by reductions in long-term repair costs.

In areas of strategic importance, such as highway belts of most modern cities, the total cost of repairs is greatly amplified by considering the indirect costs of traffic disruptions.

This article is adapted from Corrosion Basics—An Introduction, Second Edition, Pierre R. Roberge, ed. (Houston, TX: AMPP, 2006), pp. 196-197.

Editor’s note: This article first appeared on Materialsperformance.com on June 1, 2024. Reprinted with permission.