Question: What’s different when working with self-consolidating concrete and regular concrete?
Answer: Did you ever put a roof on a house? Do you use a hammer or a nail gun? When you use the nail gun, do you pound in the nail with it? Of course not, although those two tools accomplish the same thing. Five-inch slump concrete and self-consolidating concrete (SCC) also accomplish the same thing but they are different tools.
You can’t work with SCC the same way as with conventional slump concrete. It’s very different in the fresh state. Start by doing a small trial placement so you get a feel for what the concrete looks like and how it behaves. You’re going to be able to place concrete a lot faster so you need to discuss with your producer how quickly the trucks will arrive at the jobsite. Think about where you’re pouring from. For example, if you have box-outs, such as a window in a wall, make sure the concrete is flowing from only one direction until the wall below the box-out is completely full. If you start placing from the other side you’ll create voids below the box-out. Always keep it flowing in the same direction. Think about what you are casting, what you are asking the concrete to do. Are you pouring a nice open form or are you asking the concrete to do some calisthenics, to move around a lot? Because there are different performance requirements for SCC since you aren’t consolidating it, the concrete has to do that itself. And what it has to do it in — the formwork — is important. Talk about those things with the producer and have a plan in mind well in advance. With SCC, the time-dependent nature is even more important than with conventional concrete. If the truck is waiting, it’s starting to lose workability over time and it doesn’t matter if it’s SCC in the truck; it needs to be SCC when you place it.
This 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.