Diamond grinding a previously overlaid pavement allows the asphalt millings to be recycled as a gravel base. Photos: International Grooving & Grinding Association
One of several basic concrete pavement restoration (CPR) techniques, full-depth repair of distressed areas of concrete pavement can be a durable and economical alternative to asphalt overlays.
By: John Roberts
When replacing or overlaying deteriorated pavement is expected to take too long or cost too much, consider another option: concrete pavement restoration (CPR).
CPR refers to a series of engineered techniques developed over the past 40 years to rehabilitate concrete pavement. These techniques are well established for deteriorated highways, but they also offer an alternative to asphalt overlays to rehabilitate city streets. The process targets and repairs areas of distress within otherwise sound concrete pavements. CPR can be performed within small work areas and at off-peak hours, and its repairs can last for years or even decades.HOW IT WORKS
CPR is used to restore concrete pavement to its original condition without changing its grade. Unlike the typical asphalt overlay, CPR addresses the causes of pavement distress, minimizing further deterioration. Basic CPR techniques include:Slab stabilization, which restores support to concrete slabs by filling small voids that develop beneath the slab at joints, cracks, or pavement edges.Full-depth repairs, which fix cracked slabs and joint deterioration by removing a portion of the existing slab and replacing it with new concrete.Partial-depth repairs, which correct surface distress and joint-crack deterioration in the upper third of the concrete slab. A partial-depth repair involves removing the deteriorated concrete, cleaning the patch area, placing new concrete, and reforming the joint system.Dowel bar retrofits, which involve cutting slots in the pavement across a joint or crack, cleaning the slots, placing the dowel bars, and then backfilling the slots with new concrete. Dowel bar retrofits link slabs together at transverse cracks and joints, so that the load is evenly distributed across the crack or joint.Cross-stitching longitudinal cracks or joints, which repairs low-severity cracks. Reinforcing steel is added to hold the crack together tightly.Diamond grinding, which removes faulting, slab warping, studded-tire wear, and unevenness resulting from patches to create a smooth, uniform pavement profile. Diamond grinding reduces road noise by providing a longitudinal texture that is quieter than transverse textures. The longitudinal texture also enhances macro texture and skid resistance in polished pavements.Joint and crack resealing, which minimizes the infiltration of surface water and incompressible material into the joint system. Less water entering the joint reduces subgrade softening, slows pumping and erosion of subbase fines, and may limit dowel bar corrosion caused by de-icing chemicals.
In the past, many transportation agencies covered structurally sound concrete pavement with an asphalt overlay to improve the ride, optimize friction, or reduce tire noise. Diamond grinding a previously overlaid pavement allows the asphalt millings to be recycled as a gravel base or sold by the ton as reclaimed asphalt pavement (RAP) for a future asphalt project. Consequently, this process is frequently referred to as “buried treasure.”BURIED TREASURE
When applying the buried treasure concept, use the value of asphalt millings to offset the cost of removal and some of the diamond grinding cost. Every inch of asphalt generates approximately 0.05 ton of RAP per square yard. Depending on the oil content of the RAP and its proximity to a project location, this can add up to real value. Innovative owners and contractors can save money and help the environment at the same time.
In 2006, the Village of Glen Ellyn, Ill. — an affluent Chicago suburb of more than 25,000 — needed major repairs on about 29 blocks of two main city streets, both of which were 15 to 20 years old. Before the project began, the roads were 8-inch, undoweled jointed pavement with ¼-inch to ½-inch faulted joints with deteriorating joint seals. The joints were widened to 3/8-inch and then sealed atop backer rods with silicone sealant. Other methods used to repair these roads included full-depth repair, diamond grinding, and sawing and sealing the joints. In total, the project included approximately 185,000 lineal feet of joint work on both Oak Street and Western Avenue.
The Glen Ellyn Public Works Department found CPR to be more cost-effective than alternative methods. CPR allowed the department to maintain the local traffic flow with minimal disruption to the driving public. Furthermore, an asphalt overlay would have raised the height of the road, which in turn would have filled stormwater gutters, covered the monolithic curbs, and required expensive tie-ins to adjacent driveways. The owner also liked the appearance of concrete as compared to asphalt.THE NEXT GENERATION OF CONCRETE SURFACES
Tire and pavement noise has become a hot-button issue in areas with large populations and high traffic volumes. In response, public officials are seeking long-lasting, economical, and quiet pavement surfaces. The Next Generation Concrete Surface (NGCS), now in the testing stage, shows great promise in meeting these needs.
Designed to provide a consistent profile without positive or upward texture, NGCS prescribes a hybrid texture on concrete surfaces that resembles a combination of diamond grinding and longitudinal grooving. The texture can be produced through either a single-pass or two-pass operation, using diamond-tipped saw blades mounted on conventional diamond grinding and grooving equipment. These textures, used for both new construction and the rehabilitation of existing surfaces, will combine a very smooth profile and a quiet ride, as well as excellent macro texture for increased safety.
Based on the test sections constructed to date, the NGCS starts out about 1 to 4 dBA quieter than a conventional diamond-ground surface. More time is needed to fully establish the NGCS pavement's acoustic performance, but it is not expected to change during the first 10 years of service, provided the pavements are well designed and constructed with high-quality, durable aggregates.
— John Roberts (firstname.lastname@example.org) is the executive director of the International Grooving & Grinding Association.