Question: Does anyone have information on the reaction between aluminum and concrete?

Answer: Good call on the aluminum-concrete question in the October 2001 issue of THE CONCRETE PRODUCER. I, too, have a tale to tell on this topic.

Years ago, when I was working as an admixture manufacturer's representative, I received a call about the "boiling concrete" on a county bridge deck project. The client asked, "What's wrong with your air-entraining agent?" As I rushed the 30 miles to the job, I studied our admixture specification sheets and looked through my favorite concrete reference books that were balanced on my lap. I was trying to learn all I could about gas generation in concrete. Everything I read convinced me that the reported boiling could never have been caused by the air-entraining agent.

In the back of my mind I knew that a problem like this could have been caused by expansive grouts. Yet, for the life of me, I couldn't figure out why the contractor would use such a product on a bridge deck. But in my quick study, I was surprised to learn about the reaction occurs when aluminum contacts concrete.

I walked out onto the jobsite and presciently asked, "Did you use aluminum forms?" The contractor's reply was my research: "No, we used wooden forms, but we did just paint them on the inside and out with some of that good ol' Highway department aluminum paint!"

When the forms were stripped, the underside of the concrete looked like Swiss cheese. The county engineer deemed the structure sound after the contractor had repaired the underside with gunite.

Alas, I never saw the ôboilingö concrete as it had set before I arrived.

Jamie MacLaggan
Austin, Texas