CEMP-E
TI 809-02
1 September 1999
12-5. CONCRETE STRUCTURES IN CORROSIVE ENVIRONMENTS.
a. General. Corrosion of reinforcing steel and other steel in concrete causes not only
damage to the reinforcing steel, but also damage to the concrete. Rust that forms during the
corrosion process has a volume several times that of the parent material. This generates
expansive forces that causes spalling and delamination of the concrete. Chloride ions, most
often attributed to a salt water, or salt spray, are the major cause of reinforcing steel corrosion.
As with structural steel the contact between dissimilar metals, and also between exposed steel
and embedded reinforcing steel, can lead to corrosion that can damage both the steel and
concrete. The high alkaline environment of concrete protects reinforcing steel, prestressing
steel, and other embedded steel from corrosion provided the concrete is durable, has low
permeability, and provided there is adequate concrete cover. Additional information of the
corrosion of concrete reinforcing steel can be found in ACI Committee 222 Report, "Corrosion
of Metals in Concrete".
b. Concrete Cover. Concrete in a marine environment and subject to salt-water wave
action and spray should have concrete cover protection greater than that specified in ACI 318.
For concrete walls that at 500 mm (20 inches) or greater in thickness the minimum concrete
cover will be 65 mm (2.5 inches). If possible the cover should also be 65 mm (2.5 inches) in
concrete walls that are less than 500 mm (20 inches). For concrete that is not placed within
forms, or for concrete in contact with earth, the cover requirements will be increased 15 mm
(1/2 inches). However in thin members where clearances are restricted the cover can be
limited to the maximum of either:
(1) 1.5 times the maximum size of aggregate, or
(2) 1.5 times the maximum diameter of reinforcement, or
(3) 20 mm (3/4 inch) cover to all steel including stirrups.
Additional information on reinforcing steel and prestressing steel detailing for structures in
marine environments, and for the design of reinforced concrete structures in marine
environments, can be found in ACI Committee 357 Report, "Guide for the Design and
Construction of Fixed Offshore Concrete Structures".
12-6. CONCRETE STRUCTURES PROTECTING THE ENVIRONMENT.
a. General. Concrete building features that must be designed to protect the
environment from chemical spills, or to protect water supplies from contamination, will be
designed in accordance with the provisions of the ACI Committee 350 Report, "Environmental
Engineering Concrete Structures". These features include tanks, reservoirs, sewers, wet wells,
pump stations, and other similar structures and appurtenances. The main purpose of ACI
Committee 350 Report is to minimize cracking to avoid leakage of chemicals and wastewater.
b. Design Approach. In accordance with the ACI Committee 350 Report the design
strength required by the ACI 318 load factor equations is to be multiplied by a durability
coefficient equal to 1.3 to obtain the required design strength for environmentally engineered
concrete structures. The purpose of the durability coefficient is to reduce reinforcing steel
12-3
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