Reinforced Concrete: CP

The pH of environment in concrete usually is greater than 12.5, which causes a passive film on the surface of embedded steel reinforcement. However, this protective film breaks down when concrete reacts with atmospheric carbon dioxide or chloride ions (present in aggressive environments such as seawater or de-icing salt) penetrate into the hardened concrete and reach the surface of reinforcing steel.

The chloride threshold

The chloride threshold for the initiation of pitting corrosion for a given structure depends on numerous factors. Major factors have been identified in the pH of concrete, i. e. the concentration of hydroxyl ions in the pore solution, the potential of the steel and the presence of voids at the steel/concrete interface.

Chloride Attack

By Dr. J. P. Broomfield

Chlorides can be present in concrete for a number of reasons:

1. Contamination

-Deliberate addition of calcium chloride set accelerators
-Deliberate use of sea water in the mix
-Accidental use of inadequately washed marine sourced aggregates

ASTM C867 Criteria for Corrosion of Steel in Concrete

Degradation of Concrete

Degradation processes of concrete can be classified (Figure below) as: physical (caused by natural thermal variations such as freeze-thaw cycles, or artificial ones, such as those produced by fires), mechanical (abrasion, erosion, impact, explosion), chemical (attack by acids, sulfates, ammonium and magnesium ions, pure water, or alkali aggregate reactions), biological (fouling, biogenic attack) and structural (overloading, settlement, cyclic loading). In practice these processes may occur simultaneously, frequently giving rise to synergistic action.

Corrosion of Steel in Concrete

By Dr. J. P. Broomfield

Reinforced concrete is one of the most durable, versatile and widely used construction materials. However, occasionally it does not give the low maintenance life expected of it. Sometimes this is due to incorrect expectations, sometimes to inadequate specification or construction and sometimes due to more adverse conditions than initially expected. Consequently, there are many structures in the built environment suffering from corrosion induced damage.

Corrosion Restoration Technologies: Lifejacket

The Lifejacket system has a specially designed anode that gets encapsulated within a cavity between the existing piling and a two-piece fiberglass form

Uncoated vs Galvanized Rebar

Zinc coatings have a higher chloride (Cl -) corrosion threshold (2-4 times) than that of uncoated steel, significantly extending the time until corrosion initiation.