corrosion in reinforced concrete

Stages in Reinforced Concrete Degradation:

The following images from a steel reinforced barrier wall on a bridge illustrate different visual stages (severity levels) of rebar corrosion damage. The structure was built in 1979 and is subject to application of deicing salts in winter.

	Stage 1: Initially, the concrete appears to be sound with relatively little macroscopic cracking and no reddish discoloration from corrosion product formation.
	Stage 2: Macroscopic cracks have appeared and the concrete surface is stained by reddish corrosion products.
	Stage 3: Spalling of the concrete cover over the reinforcing steel is clearly visible, due to the formation of voluminous corrosion products.
	Stage 4: Severe spalling of the concrete cover over the reinforcing steel is evident, leaving the reinforcing steel bars directly exposed to the atmosphere.
Overall view of the advanced concrete degradation in the barrier wall. Spalling and the remains of uncovered reinforcing steel can be seen.

See more images in the reinforcing steel corrosion gallery

References/Literature:

P.K. Mehta: "Durability - Critical Issues for the Future", Concrete International, July 1997, pp.27-33.

Links:

FHWA Office of Research, Development and Technology - Document "Corrosion Protection: Concrete Bridges" at
http://www.tfhrc.gov/structur/corros/corros.htm

Concrete degradation module at corrosion-club.com
www.corrosion-club.com/concretehome.htm