Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: A490 bolts

[Subject Prev][Subject Next][Thread Prev][Thread Next]
The issue of stress corrosion cracking / embrittlement is something that nobody really understands.  One of  the concerns with respect to galvanizing high-strength steel is that  when zinc comes into contact with fresh portland cement concrete, it reacts with the alkali ingredients and generates hydrogen.  

There was a lot of concern in the prestressing industry  about using galvanized strand - it was felt that the hydrogen evolved in this reaction might enter the steel lattice and embrittle the prestressing strand. Embrittlement essentially happens when hydrogen enters the steel lattice as little atoms and combines to form a bigger molecule that disrupts the steel lattice.  Research has shown however that the zinc layer absorbs the hydrogen and prevents it from penetrating into the steel.  

Nevertheless, there is a lot of concern -  galvanized prestressing strand is not common in North America and is currently prohibited by FHWA for use in bridges. Its most common use is for barrier cables, which are not in contact with fresh concrete and are only very lightly stressed.  Galvanizing is very popular for both prestressing applications and stay cables in Europe and Japan, however.

Gail S. Kelley, P.E.