Technical Questions

ACI Committees, Membership, and Staff have answered common questions on a variety of concrete related topics.

Epoxy-coated reinforcement

Q. Why is epoxy-coated reinforcement used in concrete?


A. Steel in concrete is usually protected against corrosion by the high pH of the surrounding portland-cement paste. Cement paste has a minimum pH of 12.5, and steel will not corrode at that pH. If the pH is lowered (for example to pH 10 or less), corrosion may occur if moisture, oxygen, and chloride ions are present. Chloride ions destroy the protective layer on the steel reinforcement making it prone to corrosion. The corrosion product (rust) occupies a greater volume than the steel and exerts destructive stresses on the surrounding concrete. Epoxy coatings are used to isolate the steel from contact with oxygen, moisture, and chloride, thus preventing corrosion. Some concerns, however, have been expressed as to the cost-effectiveness of epoxy-coated reinforcement in preventing corrosion. To resist corrosion, stainless steel bars, stainless steel clad bars, or special reinforcing bars that are less likely to corrode are also available. In addition, chloride corrosion-reducing admixtures are available that raise the threshold level of chloride ion needed to initiate corrosion or to provide a barrier over the reinforcement isolating it from the environment.


References: SP-1(02); ACI 201.2R-08; ACI 222.2R-14 ACI 318-19; E2-00

Topics in Concrete: 318 Building Code; Concrete Fundamentals; Corrosion; Reinforcement

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