Diamonds Make Roller-Compacted Concrete Shine

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3 CALIFORNIA ROADWAYS
SWITCH from ASPHALT
to ROLLER-COMPACTED CONCRETE

The city of Roseville, California, USA, selected 3 diverse roadways
for a 2018 RCC pilot project … to date, has received 6 industry awards:
• Washington Boulevard: 5-lane arterial
• Atkinson Street: 2-lane collector road
• Hickory Street: Low-volume residential street

When the equipment rolls onto the jobsite, it may look like just another asphalt paving project, but … increasingly, the mix coming out of the asphalt paver is concrete—a drier mix than what comes out of a concrete mixer chute. That finished product is called roller-compacted concrete (RCC). A zero-slump concrete mix, RCC doesn’t need formwork, dowels, or rebar, and it requires minimal finishing. But it DOES need one element of traditional concrete paving—diamond grinding the surface for smoothness. Diamond grinding is the removal of a thin layer of hardened concrete pavement surface using a self-propelled machine outfitted with a series of closely spaced diamond saw blades mounted on a rotating shaft.

Diamond grinding is primarily conducted to restore or improve ride quality, but it also provides improvements in surface texture and reductions in noise levels. At one time, it was common practice to overlay RCC with asphalt, but now specifiers are taking advantage of the performance and environmental benefits of a concrete surface. When incorporating a diamond-ground surface, driving on the completed pavement will be:
• Quiet
• Smooth
• Pleasurable

The Finishing Touch

RCC was introduced in the 1970s, but the rougher surface caused it to be used mostly on industrial or service roads. Eventually, the benefits of RCC led to it being widely adopted for use on municipal streets, county roads, and parking lots, driving the need for smoother surfaces. BENEFITS of RCC:
• Effectively mixed at high volumes, then delivered to the jobsite
• Quickly and easily placed
• Vibratory rollers compact the concrete until it densifies, creating a strong, durable pavement that will resist softening, deforming, or rutting
• Offers a long service life when compared to similarly priced asphalt pavements
• Requires little maintenance
• Only minor patching in isolated areas after decades of traffic loading
• Overall reduction in lifetime cost

With so many benefits, RCC installations in the U.S. have increased across many different project types. According to research performed by Corey J. Zollinger, Chairman-RCC Pavement Council and CEMEX, between 2014 and 2016, over 1.6 million sq yd (1.3 million sq meters) of RCC were placed each year. Many of these were residential streets owned by private developers, although the method is also being used by municipalities and state DOTs, notably Texas, California, and Virginia. Zollinger said, “When used for roads where the speed of travel exceeds 35 miles per hour, RCC surfaces as installed may not be smooth enough. Diamond grinding smooths the pavement surface, making it suitable for higher speed travel.”

In addition to improvements in RCC surface texture through diamond grinding, recent years have seen improvements to mix design, mix production and placing, as reported in Zollinger’s paper “Recent Advances and Uses of Roller Compacted Concrete for Pavement Construction in the United States”. In metropolitan areas with mature markets, the demand for RCC has allowed concrete suppliers to supply RCC from fixed locations, as opposed to mobilizing plants and paving equipment to the project site, making smaller projects feasible.

Roller-compacted concrete pavement after diamond grinding. Photo Courtesy: Corey J. Zollinger

Choosing RCC

The city of Roseville, California, USA, selected 3 diverse roadways for a 2018 RCC pilot project that, to date, has received 6 industry awards:
• Washington Boulevard: 5-lane arterial
• Atkinson Street: 2-lane collector road
• Hickory Street: Low-volume residential street

More than two miles of failed sections of existing asphalt pavement distributed across the three roadways were reconstructed using RCC, helping this project achieve several “firsts” in California.

The roadways were originally constructed in the early to mid-1900s and as Roseville grew and developed, piecemeal paving work resulted in varying levels of pavement quality. Potholes and roughness were ongoing problems in several locations and resident complaints were requiring the city to make too-frequent repairs. Eventually, the number of lane miles needing repair far outstripped the funding available and a backlog was developing. At that point, the city wanted to switch to a more durable concrete pavement. Any concrete solution considered, however, had to be cost-competitive.

Noah Siviglia, Associate Engineer-Department of Public Works—Engineering, City of Roseville said, “We extensively researched roller-compacted concrete. RCC is a good option when working in a developed area, because there are no long road closures while the concrete cures—it’s a very hard surface almost from the moment it comes out of the machine. As compared to traditional portland cement concrete pavement, the lane or road closure duration can be far reduced.”

• Before construction, the team developed a concrete mix design that was able to reach the city’s specification of at least 2,500 psi unconfined compressive strength within two days, allowing the roads to be fully opened to traffic quickly
• Intersections were opened by the end of each work shift for cross-traffic
• Early entry saw cuts were made to create joints while the pavement was still green (although because the concrete used for RCC is a dry mix, minimal pavement shrinkage occurs)
• Dowel bars were not used in the design
• Pavement designers relied upon aggregate interlock for load transfer
• Finished RCC surface was then diamond ground across the entire surface to correct ride deficiencies, increase
friction, and reduce tire/pavement noise, leaving the standard, corduroy-like surface texture
• Rapid construction was a priority, to stay on schedule
For more details on the Roseville, Ca road projects, please go to: www.roadsbridges.com/diamonds-make-roller-compacted-concrete-shine.

After the project was complete, in fall 2018, the city received positive feedback from local drivers due to the minimal project disruption and smooth ride.

Siviglia pointed out, “RCC gives cities another option for their paving projects—and having options always helps keep costs competitive.”

John Roberts, Executive Director-International Grooving & Grinding Association (IGGA). It is interesting to note that diamond grinding was first used in California in 1965 on a then-19-year-old section of I-10 to eliminate significant joint faulting and ride quality issues. This was followed by subsequent grinding events in 1983, 1997, and 2017, helping to preserve a nearly 75-year-old concrete pavement that still serves the traveling public today. I believe that the durability of RCC, paired with a diamond ground surface finish, gives these pavements the DNA to exceed that longevity milestone.”

Award-Winning Project

Installation of roller-compacted concrete in the city of Roseville. Photo Courtesy: Corey J. Zollinger

Roseville’s roller-compacted concrete (RCC) pilot project has been the recipient of six awards:

IMPORTANT LINKS:
Roads&Bridges article titled “DIAMONDS MAKE ROLLER-COMPACTED CONCRETE SHINE”: https://www.roadsbridges.com/diamonds-make-roller-compacted-concrete-shine
Corey Zollinger’s PAPER: www.rollconllc.com/wp-content/uploads/Recent-Advances-Uses-of-RCC-in-US.pdf

ISCP article titled “4 Studies Show Environmental Benefits of CGR “Slurry””: www.concretepavements.org/2020/02/22/4-studies-show-environmental-benefits-of-cgr-slurry/

Home Page Photo 1: A Closeup of Diamond-Ground Concrete Pavement. Courtesy: John Roberts

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