“I’ve been puzzled for years over why internal curing isn’t used more often,” says John Ries, Technical Director of the Expanded Shale, Clay, and Slate Institute (ESCSI), with a slow shake of his head. “IC works…it’s really a no-brainer.” For his 20+ years of pushing internal curing to the point where today it is beginning to gain acceptance, he is one of The Concrete Producer’s Most Influential People of 2017.
“We started to learn about this in the 1950s—Bob Tobin did some research on it,” says Ries. “One of the things he learned was that lightweight concrete is very forgiving. They had placed lightweight concrete on a metal deck and to get it to pump they had added a lot of water that was forced into the LWA. The expectation was that it wouldn’t make strength but it still did due to the effects of internal curing (IC).”
This prompted ESCSI to support research to prove that IC worked and to determine why it worked. Dale Bentz at NIST and Jason Weiss at Purdue University identified the mechanisms and the benefits. “They were able to prove that IC eliminated autogenous shrinkage as well as other benefits. Today there have been at least 100 bridge decks placed using IC and they are mostly crack free. The New York and Indiana DOTs are using it, along with the Denver Water Board on tanks. So the snowball is starting to roll downhill!”
Ries is quick to point out that IC does not replace surface curing. “Internal curing supports external curing. It’s below the surface so it promotes complete hydration and reduces curling and shrinkage both at an early age and over the long term. It’s simple and proven and not expensive—less than $10 per cubic yard for the ESCS material.”
Since it was proven to work years ago then why has it taken so long to be recognized? “Producers have been reluctant to use it,” he says. “It requires another bin for lightweight fine aggregate, it needs to be wet when it goes into the mixer, and it requires some additional QC. So that’s one reason, but also the DOTs are very conservative.”
Another common question about using lightweight aggregate is if the industry has the capacity to meet the demand, something producers are especially sensitive about in the age of fly ash shortages. “There’s plenty of capacity by the ESCS producers,” Ries insists. “They have 4 million cubic yards of excess capacity right now and even if 100% of concrete pavements used IC, it would only consume about 1.5 million cubic yards of lightweight.”