“I’ve been puzzled for years about why internal curing (IC) isn’t used more often,” says John Ries with a slow shake of his head. “It works. It’s a no-brainer.” For spending more than 20 years promoting internal curing, using saturated lightweight aggregate, to the point where it’s finally beginning to take off, Ries is one of the 2018 Most Influential People in the Concrete Industry.
Ries began advocating for lightweight aggregates (LWA) in 1986 working for Utelite, an expanded shale manufacturer in Utah. Having grown up on a cattle ranch in northern Montana and graduated with a civil engineering degree from Montana State University, he liked lightweight aggregate’s inherent sustainability. When he was offered the job as president of the Expanded Shale, Clay, and Slate Institute (ESCSI) in 1989, he took it on the condition that he could stay in Utah. So ESCSI moved to Salt Lake City.
While the most common applications are concrete masonry units and lightweight concrete floors, ESCSI also is used for asphalt chip seals, soil conditioners, and lightweight fills. It’s most intriguing application, though, is as an internal source of moisture for curing concrete.
“In the 1950s, Bob Tobin learned that lightweight concrete is very forgiving,” says Ries. “Researchers placed lightweight concrete on a metal deck and, to get it to pump, they forced a lot of water into the mix. They didn’t think it wouldn’t make strength, but it did due to internal curing. Even so, it wasn’t promoted until the early 1990s. George Hoff was looking for a way to reduce concrete density to make the Hibernia oil platform in Newfoundland more buoyant. He added lightweight aggregate, expecting the strength to go down, but instead it went up.”
This prompted ESCSI to support research by Dale Bentz at NIST and Jason Weiss at Purdue University on why internal curing works. “They proved it eliminates autogenous shrinkage as well as other benefits. At least 100 bridge decks have been placed and they are mostly crack-free. The New York and Indiana transportation departments use it, as does the Denver Water Board for tanks. It’s been used on road projects in the Dallas area and the Illinois Tollway is placing test sections. It’s also getting a lot of recognition at the National Concrete Consortium, which has members from several state transportation departments. The snowball is starting to roll downhill.”
In 2010, ESCSI hired Nick Carino to help write an ASTM specification that was approved 18 months later—very quick for committee work. ASTM C1761, Standard Specification for Lightweight Aggregate for Internal Curing of Concrete, provides a standard for defining the material, a big advantage when convincing conservative highway engineers to try something new.
Ries is quick to point out that internal curing does not replace surface curing. “It 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.”
So why has the industry taken so long to accept the material?
“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 additional QC. Also, transportation departments are very conservative.”
Another common concern is capacity, something concrete producers are especially sensitive about in the age of fly ash shortages. Ries isn’t worried.
“ESCS producers have 4 million cubic yards of excess capacity right now,” he says. “If 100% of concrete pavements used internal curing, it would consume only 1.5 million cubic yards of lightweight. And that’s fine aggregate, and we can make that easily.”