Compacted Concrete Paving (CCP) as a viable solution?
Click individually to enlarge: 1) High-density asphalt paver used to compact the dry concrete mix while paving
2) Roller used to provide final compaction; concrete then finished with a power trowel, and then broomed
Kensey Russell, P.E., Engineer-City of Mexico, Missouri said, “[Archer Daniels Midland (ADM) soybean processing facility] is responsible for Millions of dollars per year for and is critical to the city of Mexico’s economy. He stated that in 2019, we needed to serve the needs of the facility by reconstructing the road, but we also needed to include a traffic management plan that facilitated continuous operations throughout the life of the project. Traffic management was important for ADM, but also for the safety of nearby residents in terms of emergency service access.”
Years of heavy truck traffic progressing through the quarter-mile residential section to access the facility was largely to blame for the deterioration of Holt Street, and traffic management was imperative during the reconstruction. To keep traffic moving during reconstruction, crews staged alternate routes through side roads to facilitate continuous access, all while coordinating closely with the ADM facility and nearby residences—redirecting about 100 cars and 100 heavy trucks daily to ensure safety during the life of the project. Thus, the city of Mexico needed a highly efficient paving option that would withstand the test of time and the demands of industrial truck traffic for the the quarter-mile reconstruction project.
INNOVATIVE PAVEMENT SOLUTION
Even with continuous traffic management, it was critical that the project conclude as soon as possible so the industrial-residential corridor could resume normal operations. To meet this goal, the city and design consultant Bartlett & West investigated the use of compacted concrete paving (CCP) as a viable solution.
As a relatively new technology in the paving industry—never used previously within the state of Missouri—CCP combines the durability of concrete paving with the installation speed of asphalt paving and is able to be finished like conventional concrete pavement—similar to RCC, but uses finishing additives which assist in faster curing time. Installation of the project was awarded to Andale Construction of Wichita, Kansas, a leader in the construction of CCP projects.
CCP provided the benefits of both asphalt and concrete. The first generally believed to have lower initial costs, quicker to place, and open to traffic sooner; and the latter often expected to have a longer life span, somewhat more costly to place, and more time is required to open to traffic.
RCC is very well-established in the U.S., and had been very successfully used in locations in Missouri in recent years, as it places concrete in a manner similar to asphalt while having the life span of conventional concrete. RCC’s appearance and smoothness is a little different than conventional pavement options.
REFINING THE FINISHING PROCESS
CCP is a no-slump concrete that is compacted to 98% laboratory density, has a multistep finishing process, contains admixtures, and delivers a finish similar to conventional concrete. It is a well-graded mix with several additives allowing high-density modified asphalt pavers to place and compact the concrete. This paver that achieves the vast majority of the required compaction is one of the key differences between CCP and the more standard RCC. It reduces the need for the roller and the variability that is introduced with rolling the concrete. The pavement is then compacted with a finishing roller to achieve ultimate compaction. Ultimately, the city of Mexico, Mo selected CCP as the perfect solution for optimizing construction time and long-term durability.
CCP contains admixtures that reduce the water content in the concrete and also suspend water in the mix until it is mechanically activated by the paver. A patented finishing agent is also used to help provide better workability on the concrete surface without impacting the integrity of the pavement. When combined with a power trowel and broom technique, it allows for an even better finish. In the end, CCP appears just like conventional concrete pavement.
THE DESIGN PROCESS
Because CCP innovation is mainly a construction method, the design process saw very little change. The project’s overall scope involved full-depth reconstruction of the two-lane roadway, with rollover curbs to match existing curbs and minimize driveway replacements. Pavement thickness of 8 in. was chosen as the ideal depth for durability, density, and constructability.
Sidewalk on each side of the roadway was also replaced with a wider, ADA-compliant sidewalk. This was designed around utility poles located directly on the back of curb in order to stay within existing right-of-way constraints as much as possible. Permitting, stakeholder engagement, and utility coordination proceeded as usual on the project, with close collaboration and frequent communication to expedite processes as much as possible.
During construction, subgrade soil conditions were discovered to be in poor condition, with a California Bearing Ratio (CBR) of 1 and extremely saturated by periodic heavy rains during construction. Design and construction teams considered responding to the challenge with a deep undercut and aggregate stabilization, but that was considered cost-prohibitive and impractical considering the presence of subsurface utilities. The teams moved forward with a 10-in. cement stabilization, which proved the most feasible and efficient option for improving the subgrade.
INNOVATIVE FUNDING
While time was of the essence, so was funding. The city identified the Federal Highway Administration (FHWA)‘s Accelerated Innovation Deployment (AID) Demonstration program as a possible source of funding—provides funding as an incentive to accelerate the implementation and adoption of innovation in highway transportation. The design consultant followed up with preparing and coordinating an application through the Missouri Highway and Transportation Department (MoDOT) and due to the innovative nature of CCP, the Holt Street project was deemed a strong candidate for AID funding. The AID grant covered 80% of the project costs and was successful.
Steve Schultz, P.E., Engineer-Bartlett & West“ helped the city secure the grant and stated, “To meet the grant criteria, we used compacted concrete paving, hosted a meeting on the day of paving for industry partners to observe and learn, and prepared a final report for FHWA to recap lessons learned from this innovative project.”
THE CCP vs. CONVENTIONAL CONCRETE
The use of CCP allowed for:
• All paving operations to occur in a single day
• Cure time was minimized due to the innovative material meeting a required compressive strength sooner than traditional materials would have. It was thought that Holt Street could have reopened within 2 days of construction, but because an adequate traffic management plan was in place, alleviating some of the schedule pressures, the project team chose a more conservative approach with a 7-day cure time, allowing pavement to achieve 4,600 psi before reopening.
• Relatively dry mix allowed the project to achieve a rapid early strength—limiting the downtime of grain trucks accessing the ADM facility
• Unique characteristics made CCP more desirable than traditional concrete pavement:
– No reinforcement
– No formwork
– Laying method resembling that of asphalt
Russell said, “Data shows we saved at least a 1/2-day of production time by using compacted concrete paving, and preserved emergency access for our residents. There is no doubt the CCP method made a difference on this short—but very important—corridor for the city of Mexico.”
For the full article titled “Reconstructing a Missouri Road with Compacted Concrete Pavement”, please go to: www.roadsbridges.com/reconstructing-missouri-road-compacted-concrete-pavement