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Dangerous Corrosion of Embedded Aluminum Posts in Hi-Rises
A discussion started in 2003 and continuing through 2017 . . .(2003)
Q. We have, what appears to be, a corrosion problem occurring on coated Aluminum handrail post, that are embedded approximated 2-1/2" to 3" into the top a 8" wide poured concrete knee wall. The corrosion has expanded to the point that it has caused the concrete to spall from the wall; some chunks 2-3" thick x 10-12" long. The fracture occurs at the posts and emanates outwards at a (+/-) 30-degree angle. The posts are 1.8" x 1.8" (snap together type) Aluminum alloy 6063-FHS-T6 (possibly manufactured by Easco Aluminum). The setting cement is Bonsal Commercial Anchor Cement, "a polymer modified shrinkage compensating hydraulic cement-based product", which according to Bonsal "has been formulated not to contribute to the corrosion of Aluminum". The Aluminum posts are coated with "Morton Poyceram 1400 as its standard finish. This finish is a baked polyester enamel coating which is manufactured to meet or exceed AAMA specification 603.8". There is no sealant at the base of the post, where it meets the Bonsal grout. Water most likely settles between the post and the setting cement. The project is approximately two miles from the Gulf of Mexico. Salt spray is probably the corrosive agent, but how is it penetrating the coating? There are nearly 700 posts in question. We have removed the spalled concrete and examined the posts. The coating has become a white powder and has separated from the post and is attached to the grout. The posts are pitted at the corroded areas.
This a safety issue. The spalled concrete may fall from the 8th floor; and corroded rails may not be adequate in the future. We have more hi-rises under construction and want to eliminate it before it is incorporated into the next building Thanks. Any help and advice will be appreciated.Ed Johnson
Director of Construction, General Contractor - Fort Myers, Florida, USA
A. The polymeric coatings will never protect your posts, as they are largely barrier coatings. You need a sacrificial coating beneath the polymer, such as cadmium or pure aluminum, protected further with a chromate conversion coating. As cadmium is a carcinogen, I would suggest you consider IVD aluminum. You can find a number of companies that can do the coating and chromate conversion work for you on this website.
- Vista, California
A. As a structural engineer, I recommend you not use aluminum in contact with concrete, the white powder might be aluminum hydroxide (I got this from a web site - members.aol.com/chrushstone/cor_aclz.htm), which is what is degrading the concrete by causing expansion underneath the railing/concrete connection and causing the concrete to eventually burst and spall. This corrosion is exacerbated by the presence of sodium chloride (salt) blown in from the ocean.
Stainless steel is routinely used in water and waste water treatment plants to prevent an aluminum reactivity issue when embedded into concrete.
The problem with the railing is a life-safety issue possibly involving someone falling to their death after leaning on the railing. There is also the possibility of passersby below being killed by falling chunks of concrete if they are large enough and fall from a large enough height. It is also possible, depending on how the concrete is designed to support the balcony that the spalling is destroying the concrete's load bearing capacity and leading to an eventual collapse.
You should have a structural engineer or a forensic testing company take a look at the situation.
- Minneapolis, Minnesota
July 2, 2009
Q. What compound can be safely used to "re-anchor" loose aluminum railing? Thanks!Robin Dreggors
- St. Simons Island Georgia USA
July 5, 2009
A. Hi, Robin. Although I can't speak from my own experience or my own knowledge of the codes, I think the previous response is suggesting that the problem is not solvable, i.e., that you cannot safely embed aluminum in concrete.
When I see aluminum railings, it seems they are bolted down with stainless steel anchor bolts.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
February 13, 2017
Q. Dear Sirs: I am involved in the design of 6005-T5 aluminum parts that get embedded in concrete. Is Alodine finish a suitable anti-corrosive barrier for the aluminum parts for this condition? Can you direct me to a site with the Alodine on aluminum anti-corrosive properties? Thank you. Steve.Steve Gernes
- New Brighton, Minnesota, USA
A. Hi Steve. Alodine is a Henkel Corporation trade name for their line of chromate conversion coatings for aluminum.
Hopefully they can give you specifics; otherwise search for "chromate conversion coating of aluminum", "chem-film" (a term used mainly in the USA), or Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil]. But we do have a posting above which says aluminum should not be imbedded in concrete.
Ted Mooney, P.E. RET
Pine Beach, New Jersey