Economical and Crack-Free High-Performance Concrete for Pavement and Transportation Infrastructure Construction

The Missouri Department of Transportation, in conjunction with the Missouri University of Science and Technology, recently researched the behavior of a new class of environmentally friendly and cost-effective high-performance concrete (HPC) they refer to as Eco-HPC.

"Internal curing is featured in MoDOT's report as one of the key strategies for reducing the amount of cracking that occurs in concrete structures and concrete pavements," notes Trinity's Jeff Speck. "They're trying to come up with longer lasting concrete, concrete that is what we call sustainable. They want projects to last a hundred years now instead of 50 years."

Speck says one way to extend the service life of concrete is to reduce the amount of cracking. "Reducing early age cracking is one of internal curing's key benefits, " says Speck. "Internal curing extends the hydration process of the cement. The internal moisture goes into the concrete in the form of absorbed water in lightweight fine aggregate."

He notes that concrete often falls apart because water, salts and other corrosive materials get into the concrete through cracks. "That starts the corrosion process in reinforcing steel. As the steel rusts, it expands and it disrupts the integrity of the concrete and eventually it has to be torn out and replaced," Speck says. "Another interesting point is that the researchers that wrote the report for MoDOT came to this conclusion without any prompting on the part of the lightweight aggregate industry at all," he says.

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Major Points

  • The incorporation of 25% LWS [presoaked lightweight sand] was shown to be fully effective at reducing shrinkage rate and magnitude. No shrinkage was obtained for slab made with 20% SL [slag] and 35% FA [Class C fly ash] containing 25% LWS. This slab exhibited higher relative humidity after 30 days of drying compared to the other slabs made without any LWS. The lowest relative humidity values observed for the FA25, SL20FA35-25LWS, and SL20FA35-7.5EX-0.35FRW mixtures were 82%, 96%, and 90%, respectively. This confirms that the combined use of SCM replacement and LWS can be fully beneficial at reducing shrinkage rate and magnitude.
  • The synergetic [sic] effect of the combination of shrinkage reducing materials, including LWS and EX [expansive agents] coupled with fibers (synthetic fibers or recycled steel fibers) is quite effective to design low cracking potential concrete. The internal curing provided by the LWS can reduce the shrinkage and risk of early-age shrinkage cracking, especially for mixtures subjected to air drying without using any initial moist-curing.
  • Eco-HPC mixtures made with proper combination of SCMs coupled with shrinkage mitigating materials can lead to crack-free properties (limited crack width of 0.1 mm (0.004")) with high resistance to shrinkage cracking. Based on the obtained results from this study, the use of 25% LWS or 7.5% CaO-based EX is quite effective in developing Eco-HPC with low risk of cracking.
  • The strength gain resulting from initial moist curing period (IMCP) was found to be more critical for mixtures containing high volume SCMs, which caused the highest spread in compressive strength. The use of 25% LWS replacement was shown to compensate for the drop in compressive strength resulting from the absence of IMCP.

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