What are Corrosion Protection Systems for Reinforced Concrete?
Corrosion protection systems are measures that keep the steel in reinforced concrete from rusting.
Why the steel needs protection
The concrete cover normally keeps the pH around the steel above 12, and this avoids the corrosion reaction. Carbonation from the surface and salt can break this protection down, and too little cover makes this more likely. Rust takes up more volume than the steel it forms from. It causes cracking, spalling and in the end structural failure (Wikipedia ).
Options
Correct concrete cover is the first measure. Too much cover is also a fault, because it gives wider cracks. Where salt is present, the bars can be epoxy-coated, galvanized or stainless steel. These cost more at first and less over the service life. Damage to an epoxy coating reduces its long-term resistance.
Airfield pavement
FAA specification Item P-501 for cement concrete pavement lists epoxy-coated reinforcement among the options that the Engineer can designate (ASTM A775, A934 and A884). Each dowel bar must be epoxy coated to ASTM A1078 Type 1, with a cured coating more than 10 mils thick. The Engineer may require more protection, for example chromium or stainless steel dowel and tie bars. This extra protection needs coordination with the FAA first.
Steel in airfield lighting
A steel light base can be hot dip galvanized. If the zinc layer gets damaged, the steel rusts quickly. A cold galvanizing compound protects less well than factory hot dip galvanizing. Some de-icing chemicals make galvanized products corrode faster. EASA lists corrosion among the routine ground checks of an aerodrome lighting system.
Frequently Asked Questions
- Why does steel in concrete not rust normally?
- The concrete cover around the steel normally keeps the pH above 12, and this avoids the corrosion reaction. Too little cover lets carbonation from the surface and salt reach the steel. Too much cover can cause wider cracks, which also weaken the protection.
- Which corrosion protection does FAA specification P-501 give for dowel bars?
- Before delivery, each dowel bar must be epoxy coated to ASTM A1078 Type 1, with a coating thickness after curing of more than 10 mils. After coordination with the FAA, the Engineer may require more protection. Examples are chromium dowel and tie bars to ASTM A1035 or stainless steel dowel and tie bars to ASTM A955.
- Can de-icing chemicals damage airfield lighting hardware?
- Yes. FAA AC 150/5340-30J says that some de-icing chemicals may cause faster corrosion of galvanized products in in-pavement lighting systems. The same text says that they may also damage cables and deteriorate connections.
References
- wikipedia-rebar
- Rebar Wikipedia
- faa-ac-150-5370-10h
- AC 150/5370-10H, Standard Specifications for Construction of Airports, Item P-501 Cement Concrete Pavement FAA
- faa-ac-150-5340-30j
- AC 150/5340-30J, Design and Installation Details for Airport Visual Aids FAA
- easa-ear-aerodromes
- Easy Access Rules for Aerodromes (Regulation (EU) No 139/2014) EASA
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