Highlands Ranch, Colo., lies 12 miles south of Denver in Douglas County. Because it is a master-planned community, most of the infrastructure for this 22,000-acre urban area was built during the early 1980s. This meant that a significant number of the community’s roadways reached the end of their roughly 25- to 30-year design lives at the same point in time.
Facing a large quantity of repair work, the county conducted extensive research to identify practical repair options that would also improve ride quality and extend pavement life. A forensic study on five different sections of concrete roadways in Highlands Ranch revealed that four sections had a range of problems, including broken panels, joint separation, transverse joint faulting, and cracking.
“Once the problems were identified, the county conferred with several different institutes and agencies to gain an understanding of repair options that would also reduce required maintenance,” says Karl Lucero, pavement management engineer with the Douglas County Department of Public Works Engineering. Those entities included the Portland Cement Association, American Concrete Pavement Association, International Grooving & Grinding Association, Colorado Asphalt Pavement Association, and the Colorado Department of Transportation.
Based on those discussions, Douglas County chose to use concrete pavement preservation (CPP). The county had previously used CPP methods on several smaller projects with good results.
As a result, in late 2013 Douglas County embarked on one of the largest concrete pavement preservation projects ever undertaken by a U.S. county.
The CPP solution
Concrete pavement preservation is a series of engineered techniques developed during the last 40 years to manage the rate of pavement deterioration in concrete streets, highways, and airports. It is a non-overlay option used to repair targeted areas of distress in pavement without changing its grade. This means curbs, gutters, bridge clearances, approach slabs, and roadside appurtenances do not need adjustment.
The preventive procedures restore pavement while also extending pavement life. By removing broken concrete and restabilizing the subgrade before replacing the pavement, CPP techniques also address some of the causes of pavement distress, such as saturated subgrade or missing dowels in the transverse joints, thus minimizing further deterioration. In contrast, merely covering the distress with bituminous patches or an asphalt overlay does not correct the cause of the distress; it will eventually manifest itself again, usually as a larger, more expensive problem.
Typical CPP techniques include slab stabilization, partial or full-depth repairs, dowel bar retrofits, cross-stitching of longitudinal cracks or joints with rebar, diamond grinding and grooving, and joint and crack resealing. (For more on these techniques, see the sidebar at left.) Douglas County engineers chose to use full-depth repairs, dowel bar retrofits, diamond grinding, and joint resealing to repair roads.
CPP in Douglas County
The large-scale, two-phase project included 66 lane-miles of concrete pavement to be repaired, distributed across two sections with seven lanes and five sections with five lanes. The pavement was 7.5 inches thick with transverse joint spacing at 15 feet over a 75,000-square-yard area. Due to its age and repeated load, the pavement joint exhibited transverse faulting.
The county contracted Denver-based concrete paving company Villalobos Concrete Inc. to remove and replace all severely cracked or broken slabs. Crews also increased the load-carrying capacity of the pavement by retrofitting dowel bars in locations where there were none. In two areas, the pavement condition warranted complete removal of the roadway. The contractor removed the subgrade to a depth of 3 feet and replaced it with a recycled concrete base course. Where needed, trench drains were installed behind the curb.
During the second phase of the project, general highway contractor Interstate Improvement Inc., Faribault, Minn., performed grinding followed by an aggressive joint resealing program to provide a safe, smooth, and quiet ride for motorists. Crews used diamond-grinding equipment over 500,000 square yards of existing pavement surface, sawed and sealed 1,058,400 linear feet of concrete pavement joints, and replaced all pavement marking (using 2430 gallons of pavement marking paint and 5385 square feet of methyl methacrylate).
The project cost $5 million for concrete panel removal and replacement and $3.5 million for grinding, joint sealant, and striping. The work was performed under two 90-day contracts. The concrete panel repairs were completed on time. The grinding contract, however, was delayed due to heavy rainfall, early snow, and cold. This project will restart this month (April 2014) and is scheduled to be completed by the end of May 2014.
Working with local roads
Public agencies benefit from CPP treatments because they can be designed and packaged for bid in a matter of days. Plus, they typically cost far less than alternative repair treatments.
However, local road repair projects differ somewhat from those of larger interstate projects. Traffic flow within developed areas such as Highlands Ranch depends upon a street hierarchy: Residential streets feed into collector roads, which, in turn, connect to arterials and then freeways. The work in Douglas County had to be scheduled and performed to maintain traffic movement within the road network as well as provide access to local businesses, schools, and residences.
Fortunately, because pavement preservation methods are used to repair only those areas that need improvements, the isolated repairs require fewer traffic control measures and cause less traffic disruption.
In October 2013, the Portland Cement Association Rocky Mountain Region, the Colorado/Wyoming Chapter of the American Concrete Pavement Association, and the International Grooving & Grinding Association co-hosted an open house featuring the Highlands Ranch project. The event kicked off with an educational presentation and then proceeded to the project site for a tour of the pavement repair and grinding areas. Equipment demonstrations and question-and-answer sessions gave attendees a clear picture of the CPP techniques being used on the roadways.
Informational events like the open house will help best practices spread, and it is likely that the future will see a wider adoption of CPP by county and municipal entities.
Kristin Dispenza is an AEC editorial specialist with Constructive Communication Inc.