Durability and Serviceability

Owners are looking for low-maintenance structures that look good — and function well — over the long run. There are many ways serviceability can be built into designs, for maximum serviceability and durability includes careful attention to crack control, and use epoxy-coated reinforcing bar in corrosive environments.

Corrosion Protection

Steel is manufactured by heating iron ores that are primarily iron oxides along with other ingredients. This heat transforms the iron oxides into the metallic iron. Corrosion of steel is a natural electrochemical process whereby the metal reverts back to its original oxide state. When steel is placed into concrete, it develops a surface passive oxide film, due to the high pH of the concrete. This passive film prevents further corrosion of the encapsulated metal. The film may be disrupted by carbonation of the cement paste, which reduces the pH, or through the ingress of chloride ions into the concrete, from either deicing salts or sea water.

As the steel corrodes, the released iron ions react with oxygen and water to form expansive iron oxides that may occupy up to seven times the volume of the initial metal. This expansion may cause the surrounding concrete to crack, leading to delamination and spalling.

Epoxy Coated Rebar

From a structural perspective, reinforced concrete structures are highly reliable. However, when exposed to deicing salts or saltwater, reinforcing bars can corrode, leading to possible accelerated deterioration of the structure.

Researchers have considered many solutions to the problem of reinforcing bar corrosion, but only one has emerged as the incomparable choice: epoxy coating.

For additional information explore the Epoxy Interest Group website or contact CRSI's Epoxy Interest Group Managing Director, David McDonald, directly at 847-517-1200.

CRSI Recommendations for Corrosion Protection:

Use quality concrete with adequate cover.
Specify corrosion resistant reinforcement for corrosion susceptible applications.
Consider supplemental protection systems on important structures in extremely corrosive environments.
CRSI certified epoxy-coated reinforcement suppliers assure high quality material.
Enforce specification provisions.

Stainless and Galvanized Steel Bars

There are many ways to reduce the risk of corrosion- related distress in concrete. One way is to use reinforcing bars with improved corrosion resistance over traditional unprotected carbon steel reinforcing bars. When selecting a particular type of corrosion resistant bar, issues such as level of corrosion resistance, cost, and availability should be considered. For publicly funded projects, restrictions on proprietary material and “Buy U.S.A” may be in place and should be carefully evaluated.

Stainless Steel

Between 1937 and 1941, a five-mile long pier was constructed in Progreso, Mexico. This pier is believed to be the oldest concrete structure reinforced with solid stainless steel reinforcement. Stainless steel reinforcing bars can be used where extreme corrosion resistance is necessary or where non-magnetic characteristics are needed (e.g. MRI chambers). Stainless steel bars are most frequently used where the conditions are unusually corrosive, where extended service life is necessary or where the cost due to a disruption in service is high.

The ASTM specification for solid stainless steel reinforcing bars is ASTM A955/ A955M, Standard Specification for Deformed and Plain Stainless Steel Bars for Concrete Reinforcement. This specification is applicable to a wide range of stainless steel alloys, including 304 (UNS S30400), 316LN (UNS 31653), 2205 Duplex (UNS 31803), and XM- 28/N32 (UNS 24100). ASTM A955 requires that the surface of the bars be free from detrimental imperfections; seams, surface irregularities, and the like are acceptable so long as tensile and bending requirements are met. Finally, that the macrocell corrosion test of Annex A2 in A955 be conducted on test specimens whose surface treatment, pickled or unpickled, will match that offered to the purchaser.

Galvanized Steel

Galvanization is a common method used to protect steel in corrosive conditions and galvanized reinforcing bars have been available for many years. The ASTM specification for galvanized reinforcing bars is ASTM A767/ A767M, Standard Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement. Galvanized reinforcing bar may be ordered either as straight bars that are galvanized prior to fabrication or as bars that are galvanized after the bars have been fabricated. The A767/A767M specification provides for two coating weights, a Class 1 (3.50 oz/ft2) or Class 2 (2.00 oz/ft2). However, there are no guidelines concerning the use of Class 1 or Class 2, although most transportation agencies specify Class 1.

Special considerations for the use of galvanized reinforcing bars includes “chromating,” which is reviewed in section 4.3 of ASTM 767, and air or steam wiping which facilitates the ability to bend the galvanized bars with a minimum of coating cracking. The galvanized coating is recognized as being robust enough to handle abuse, however, acceptance of galvanized reinforcing bars is dependent upon: negligible bare spots in the coating, the coating being essentially free of blisters, presence of flux spots, inclusions, dross, and acid or black spots. Additionally there shall be no spikes and bars shall not be stuck together. Note that fabrication tolerances for bend radius are larger than those specified in ACI 318, and that stress relieving may be required for tight radius bends.