Rust Spots on pea gravel concrete

[TroyB]

As part of our pool construction, we had pea gravel concrete decking installed. In one area of the decking, we are getting rust spot formation. Here is a pic:

The spots are too large to be re-bar or re-bar ties sticking up out of the concrete. Any idea what this may be. It has seemed to grow in size over the last few days.

The decking is approximately 4-1/2 months old. Thanks in advance.

 

[launboy]

Is there anything above this area of the concrete? Have you gotten any rain lately?

 

[heikejohn]

Something mixed into the concrete that wasn't supposed to be? Impurities left in the mixer & poured out with the first batch?

 

[duraleigh]

I'm not sure it's rust......I would think iron rust to be more reddish-brown.

There's a variety of cleaners that can be tried....TSP might be my first choice.

 

[dirty_steve]

We have the exact same problem and the sub that poured the deck is suppose to come by in the next few weeks and fix. A mild acid solution will remove the rust, but it will come back. We think some iron was somehow in the batch. Cleaning it works fine, but in a matter of weeks it will reapper. Keep you posted on our end.