“Internal curing may be the best thing to happen to concrete since we discovered the importance of water-cement ratio,” I heard someone say at the American Concrete Institute meeting a couple weeks ago. That’s quite a statement, I thought, and a bit of an exaggeration. But after talking with John Ries, technical director at the Expanded Shale, Clay, and Slate Institute last week, I’m beginning to think the statement may be correct.
Internal curing via the use of a small percentage of saturated lightweight aggregate provides a source of moisture inside the concrete to allow complete cement hydration. External curing water can’t penetrate the concrete, so once the free water in the concrete matrix is consumed, the concrete begins to dry out and shrink—and we know what shrinkage leads to: cracks and curling.
The concepts and evidence for the benefits of internal curing have been known for 20 years or more, but acceptance into the mainstream has been slow. “Why it hasn’t caught on has puzzled me for years,” says Ries. “I heard a presentation at one of the ACI local chapter meetings that showed it takes 20 years to 25 years to introduce a new idea into civil engineering projects and materials (concrete, roads, bridges, utilities). The electronic industry does it in one to two years.”
I suppose the 25 years has about passed, so maybe we’ll start seeing more specifications for internally cured concrete. For more information on internal curing, check out these two articles:
Curing From the Inside Out, by John Ries
Internal Curing Standard is Improving Concrete by Don Eberly
