scope:

This standard presents corrosion control guidelines that are applicable to structures made of reinforced port- land cement concrete. Reinforcing steel is compatible with concrete not only because of similar thermal expan- sion properties, but also because the highly alkaline portland cement allows a stable, protective oxide film to form on the surface of the encased steel.

If the film does not form or if it does not protect the steel, corrosion can occur. Corrosion of the rein- forcing steel can weaken or even destroy a structure.

The protective oxide film is destroyed if (1) the concrete does not fully encase the steel, (2) alkalinity is lost by reaction with aggressive gases, or (3) excessive amounts of chloride or other aggressive ions are present. If any of these conditions occurs, and both moisture and oxygen are in contact with the steel, corrosion can occur.

Corrosion ordinarily proceeds by forming an electro- chemical cell with anodic and cathodic areas, which are electrically coupled in an electrolyte, on the metal. If any one of the elements of the electrochemical cell is elim- inated, corrosion can be prevented.

Other forms of corrosion such as those caused by dissimilar metal couples and DC stray currents can initiate or greatly accelerate corrosion.

The result of the corrosion process can damage concrete in several ways.

The corrosion product of steel occupies several times the volume of the base metal. The expansive pressure exerts a significant tensile force on the surrounding concrete. Resulting cracks propagate toward either the surface or the nearby reinforcing steel, causing delamination. A small loss of steel can cause delamination, but structural integrity re- mains undiminished until corrosion has removed a significant amount of steel.

Structural integrity can be lost rapidly when corrosion occurs in an anchorage zone. Bond stresses and corrosion both put concrete in tension and are additive. Even insignificant metal loss at the surface of the reinforcing steel can be sufficient to crack the concrete cover and cause loss of bond and anchorage. Other problems caused by loss of cover include falling concrete, increased corrosion, and loss of fire resistance.

Because of the concrete damage caused by the cor- rosion products formed on reinforcing steel, the architect- engineer should consider certain corrosion criteria during the design of the structure. Design and construction considerations should be based on good engineering practices to eliminate conditions conducive to corrosion. Tests of soil and water should include but not necessarily be limited to pH, resistivity, chlorides, sulfates, sulfides, and bacteria.

This standard does not designate specific design practices for the control of corrosion because of the com- plexity of corrosion mechanisms in individual structures.

The guidelines in this standard give the architect-engineer several alternative methods of controlling the corrosion of a proposed atmospher- ically exposed concrete structure.

During the design phase of a structure that could be affected by corrosion, the services of a qualified Professional Engineer or qualified Corrosion Specialist shall be obtained so that proper materials selection and engineering practices for corrosion control are included in the design of the proposed concrete structure. His or her professional quali- fications shall include suitable experience in cor- rosion control of reinforced concrete structures. The provisions of this standard shall be applied under the responsible charge of said Professional Engineer or Corrosion Specialist.

Corrosion of the reinforcing steel in concrete and the resultant cracking and spalling of concrete cost billions of dollars each year. These losses can be reduced if proper corrosion control factors are considered during the design phase. When the architect-engineer considers the cor- rosion of reinforcing steel to be a potential problem, provisions should be made for a cost-effective corrosion control system.

Although many of the recommendations in this standard are applicable to prestressed concrete struc- tures, this standard does not fully address this type of reinforcing system.

Appendix A contains a glossary of many terms used in this standard.