In January, Illinois became the latest state DOT to adopt a paving specification for roller-compacted concrete (RCC), a very dry concrete mix with ¾-inch aggregate that’s delivered by dump trucks, placed with an asphalt paver, and compacted with a vibratory roller. Because of its high density and low water content, the material achieves high strength more quickly than conventional concrete pavement mixes.
RCC is often topped with a thin layer of asphalt. The result is a pavement that’s more durable than full-depth asphalt with a stone base course and easier for self-performing municipalities to finish and repair than conventional concrete pavement.
By approving RCC “for constructing pavement, shoulder, base course, and base course widening” as part of its Experimental Feature Program, the Illinois DOT (IDOT) was able to add RCC to its sanctioned paving practices relatively quickly.
Cities and counties can begin building roads with RCC on any project they like without having to wait for IDOT to conduct a full test project to evaluate material costs, pavement performance, and other data. More importantly, they can receive state motor fuel tax funds for projects. However those that do must provide documentation that will allow the state to track parameters, including materials, curing methods, and joint layout. They will also be required to report on their project’s long-term performance.
“It’s not a particularly fast way of getting things done, but it allows contractors and specifiers to get some experience and helps prevent the blind adoption of the latest fads or trends in road construction,” says Randell Riley, P.E., executive director of the Illinois Chapter of the American Concrete Pavement Association and contributor to the IDOT specification. The association also plans to release an RCC guide specification this summer for use by public agencies and specifiers.
Wayne Adaska, another contributor and director of pavements for the Portland Cement Association, was impressed with the speed at which IDOT reviewed and approved the new provision, a process that took only a few months. He credits the support of the concrete industry and IDOT’s diligence and cooperative spirit for helping expedite the process.
Adaska has worked with many federal, state, and local agencies in developing specifications for RCC. He is aware of at least 14 states and municipalities that have implemented specifications within the past decade. “More and more states are stepping up to the plate in providing RCC as another pavement option for their cities and counties,” he says. (For an interactive map of RCC projects in the U.S., see the RCC Explorer map at http://rcc.acpa.org.)
In Illinois, the floodgates seem to have opened since IDOT published its specification. In June 2014, IDOT plans to accept bids on a project for RCC shoulders, topped with asphalt, in the Chicago suburb of Lemont. The Illinois Tollway has also adopted an RCC specification and will be soliciting bids for truck parking areas in four oasis projects.
Four Chicago suburbs—Berwyn, Des Plaines, Franklin Park, and Summit—are considering alley and residential street applications. The third IDOT specification author, Theron Tobolski, is an adviser on these projects and, as a marketing product specialist for Bridgeview, Ill.-based concrete producer Prairie Material, has been educating public works agencies, engineers, and contractors since 2010.
“As we continue to see successful projects, the comfort level of the engineers and owners grows as they are more willing to use roller compacted concrete,” he says. Tobolski was instrumental in promoting RCC at the state level by inviting IDOT officials to visit jobsites of one of Prairie Material’s most progressive customers: the Village of Streamwood, Ill.
Durability meets fiscal responsibility
In the midst of Chicago’s coldest winter in 30 years—and almost 80 inches of snow—Matt Mann juggled snowplow schedules, monitored the salt supply, and dreaded frozen water mains. One thing that didn’t keep the public works director up at night in January was wondering if village streets could withstand the weather.
For the last four years, Streamwood has invested in rebuilding its neighborhood streets with RCC, topped with asphalt. After reading about RCC in Concrete Construction magazine, Mann and former public works director, John White, proposed the paving method to city council as a cost-saving measure. “We needed another tool in our toolbox, and we knew other states had used it successfully,” says Mann.
When he compared the cost of a typical full-depth asphalt street built to Streamwood’s standards (10 inches of hot-mix asphalt over 4 inches of stone) to an RCC base and asphalt overlay (4 inches of stone and 6 inches of concrete topped by 2 inches of asphalt), Mann estimated the village would save 15% to 20% on materials, plus the labor required to excavate the 2 extra inches required for a full-depth asphalt road.
With the council’s approval, the department tapped into Streamwood’s roadway maintenance funds to put the idea to the test. “About 20 years ago, our roads were so bad that the village appropriated a percentage of telecom tax to devote to maintaining our 100 miles of streets,” says Mann. Local funds allowed public works to use the $1.5 million generated to try out RCC in the absence of a state specification.
The first step, finding a concrete producer, proved to be the most challenging. Rather than following the usual bid process, Mann contacted local producers directly. “It took a few years, but Prairie Material ended up being the only one who could supply us with RCC,” Mann says.
RCC was relatively new to Prairie Material at the time, so the producer and public works department worked together to develop the ideal mix: 525 pounds of cementitious materials, ¾-inch maximum size aggregate, and BASF Construction Chemicals’ Delvo hydration stabilizer.
Prairie began producing the mix with a central batch plant, mixing 5 cubic yards every 90 seconds. To meet the schedule of Streamwood’s larger projects, the producer later bought two horizontal shaft spiral blade mixers, or ribbon mixers, from Dallas-based Vince Hagan Co. to produce more consistent material at a rate of eight cubic yards in 30 seconds.
Next Page: First test project