Question: Our producer tells us that the sand he is getting in our area is reactive. What does that mean when trying to place a slab that is intended to be polished?

Answer: If you’re looking at the potential for alkali-silica reactivity (ASR) in your aggregates, the first thing to consider is that admixtures can help, such as lithium-based materials. Also, consider what can be accomplished through mix proportioning — you can use fly ash or other supplementary cementitious materials to reduce the alkali level in the concrete. Again, it goes back to the pre-pour meeting. If you are placing a foundation, that’s one thing. But if you have a critical placement, like a floor that will be polished or architectural concrete, make sure you’re pulling out all of the stops not to get yourself in trouble. There are ways to pre-qualify the materials with testing way before you get into that kind of trouble. Conduct lab testing so you know what you’re dealing with. The producer will probably have test data on all the materials. There are some accelerated test methods for potential ASR. In some areas you may consider importing sand for critical jobs and that’s not that expensive.

These questions and answers were generated during the Breakfast with the Experts at the 2015 World of Concrete, sponsored by BASF. If you have problems on your jobs that you would like to pose to the experts, plan now to attend one or more of the WOC 2016 breakfasts, which have been expanded to two each day of the show.