Q. What can we tell our contractor-customers who insist on a low water-cement ratio but who then complain the concrete is hard to finish?

A. The water-cement ratio is only one variable in a concrete mix design. While it is important, it is not independent of other factors, such as total paste content and use of admixtures. The equipment and techniques used to place and finish the concrete and expertise of the finishing crew also play a role.

Each of the ingredients and their proportions and how the concrete is mixed, placed, and finished all affect the outcome.

The keys to making this work are building good relationships with your customers and then maintaining good communication. Once they buy into the idea that you’re working with them to make sure they have the right material for each application, they’ll begin to appreciate how well you know the material you are producing. And maybe then you’ll be able to move past simply discussing water-cement ratios.

Concrete’s wonderful complexity is at the heart of NRMCA’s P2P (prescription to performance) initiative.

NRMCA says designers and contractors should specify performance requirements, such as strength and finishability, and leave the mix design details to the producer. This way, the producer will have the flexibility to adjust proportions of the various ingredients, and include admixtures as appropriate to ensure the concrete suits the application.