RCC pavement is gaining momentum among contractors and road agencies due to many of its advantages, according to an article titled “Roller Compacted Concrete (RCC) Gaining Momentum” by Tom Kuennen-Equipment World’s Better Roads Newsletter. Bill Davenport, Vice President-Communications, American Concrete Pavement Association (ACPA) and ISCP Member stated, “RCC is a concrete pavement formed from a no-slump mixture, and is characterized by its unique placement methodology, which requires no forms, and no joint cutting or sealing. It’s quick to place and sets up very quickly. And it can be placed with high density pavers and compacting screeds – similar to the equipment used to place high-density asphalt pavement.”
“As soon as RCC is down and compacted, you can get at least some traffic on it,” says Eric Ferrebee, Technical Services Engineer, ACPA . “That’s because a lot of the strength is gained from the aggregate gradation, in which it packs so well it can begin carrying loads.”
RCC: The Maximum Density: Unlike conventional concrete mixes, RCC is not air-entrained, and has a lower water content, lower paste content, but larger fine aggregate content than conventional concrete. Ferebee stated, “It’s a much denser gradation. Many times the gradation is developed to achieve a maximum density. When you create that gradation, you also must consider the cement and water contents. All three tie into getting early strength and full density . . .”
In terms of density, RCC has similarities to hot mix asphalt. He adds, “In asphalt, you’re trying to achieve maximum density including voids. For RCC, we’re not so much worried about the voids as we are in achieving maximum density. Using a high-density paver and screed, right out of the paver you can get 95% of maximum density, and then use rollers to bring up to 98 or even 100% of maximum density. That’s what we’re going for. Strength and long-term durability comes with maximum density. If you are achieving 98 to 100% of target density, you will achieve your goals of strength.” RCC will attain a compressive strength of 4,000 psi within a few days, but can be opened to traffic almost immediately.
RCC owes much of its economy to high-volume, high-speed construction methods. It can be blended in continuous-mixing pug mills at or near the construction site. The high-output pug mills have the mixing efficiency needed to evenly disperse the relatively small amount of water used.
SEVERAL ACTIONS HAVE PROMOTED RCC USE:
• The RCC Pavement Council was founded to underwrite marketing and research into RCC pavements
• ACPA’s RCC Task Force released an updated RCC guide specification: “Roller-Compacted Concrete Pavements as Exposed Wearing Surface” (PDF) (Version 1.2)
• ACPA began developing an RCC “wiki page”
• The Federal Highway Administration’s (FHWA) “Highways for Life” program released a report on an RCC demonstration project in Arkansas (PDF)
• ACEiT Concrete Paving Technology introduced an admixture that aids RCC compaction and densification while minimizing roller marks
• Solomon Colors’ RCC Surface Pro nano-silica admixture enables RCC to be troweled smooth or broom textured, providing a more aesthetic surface appearance than conventional RCC
Conventional dump trucks transport the RCC into a high-density paver, which places the material in layers up to 10-inches thick. The material will be dry enough to support a vibratory roller immediately after placement, yet wet enough to permit adequate distribution of cement paste. Compaction is the most important stage of construction, providing density, strength, relative smoothness and surface texture. Curing ensures a strong and durable pavement and it makes moisture available for hydration—the chemical process that causes concrete to harden and gain strength. Basically, if subgrade condition is good enough for an asphalt or concrete placement, it’s good enough for RCC.
Andy Johnson, PhD, P.E., Pavement Design Engineer PCA, “RCC has a great deal of potential as an economical, rapid, and durable paving material. By using grinding to achieve a smooth, quiet surface, we can use RCC in a much wider variety of situations without the added cost of a hot mix asphalt surface layer.”
To read the entire article titled “Roller Compacted Concrete (RCC) Gaining Momentum”, please go to: http://www.equipmentworld.com/roller-compacted-concrete-gaining-momentum/.
ISCP home page photo: Tom Kuennen: At RCC demo at Tennessee DOT: 6-in RCC;
Variable widths; all compaction obtained at the screed; & tandem roller smoothed surface without vibration.