Roller compacted concrete (RCC) is an increasingly attractive alternative to traditional hot-mix asphalt (HMA) and portland cement concrete (PCC) for a variety of pavement projects. A lot of interest has been generated by a series of demonstration placements in Chattanooga, Tennessee, using various RCC mix designs and new advances in technology including a proprietary additive, HexiCrete RCC 550, from Momentive Specialty Chemicals.
The city of Chattanooga and one of its engineering managers, Ariel Soriano, PE, have led the way in testing RCC. Soriano and his team (including local and national RCC experts) have recognized the importance of pavement life in calculating long-term roadway project costs. Preventive maintenance and capital budgets are typically short in today’s budget-cutting environment, putting a premium on designing for longer service lives.
"One of the ways to get a pavement that lasts 50 years or more is with improved construction materials such as RCC," Soriano says. "Momentive’s product line can be instrumental in maximizing the overall quality of RCC pavements (like density and strength parameters) which will help maximize service lives."
The city began working with Momentive in March 2008 on a series of test placements with positive results. RCC 550 was evaluated in a test section of Chattanooga’s first contract RCC project—Northpoint Boulevard, Phase I—and demonstrated accelerated densification, up to two times faster than untreated RCC, meaning fewer roller passes.
The first major arterial RCC 550 project was the new Volkswagen plant connector road, which carries a high density of traffic equivalent to that on a state highway.
During this project, 4,400 cubic yards of RCC were placed along the 2,260-foot-long roadway. Even with a high-density paver in use, RCC 550 was added to ensure proper compaction of the nine-inch-thick RCC.
A nuclear density gauge indicated less of a surface-to-mid-depth density gradient immediately behind the paver with RCC 550 in the mix. "We were optimizing the paver’s compaction energy and reducing roll-down potential," says Soriano. "The result—a smoother surface that did not require drastic asphalt leveling course thickness adjustments to smooth out the ride."
Soriano believes that, compared to conventional pavement materials, RCC mix designs utilizing Momentive’s additive can increase service life by up to three times, or match conventional pavement service lives for 60–70% of the cost based on actual contract prices. Six inches of RCC with an asphalt overlay has been shown, through deflection testing, to be structurally equivalent or superior to fifteen inches of aggregate plus five inches of asphalt.
In the end, after analyzing a combination of core thickness, ground penetrating radar (GPR) and falling weight deflectometer (FWD) data on five RCC projects of varying thicknesses, Soriano found that the RCC structural coefficient value was in the range of 0.64 to 0.73. This indicates a stronger, longer-lasting structure than other pavements such as HMA (0.40–0.44) and PCC (0.50 per the concrete industry).
RCC 550 additive comes with another benefit. "Momentive’s technical staff was very helpful in implementation and incorporation of the RCC 550 in the RCC mixes," Soriano says. "They were actively working through issues with concrete plant personnel and resolving them quickly and safely."
The HexiCrete line of products from Momentive is an innovative range of additives designed to improve concrete performance, contractor productivity and environmental suitability. The line consists of:
For more information contact Momentive at: +1 425 372 9086 or +1 425 378 8600. Or click here for our HexiCrete overview video.
Momentive Specialty Chemicals Inc.
180 East Broad Street
Columbus, OH 43215-3799