Concrete Pavement Resurfacing
Resurfacing, or overlays represent a more extensive series of activities to rehabilitate a concrete pavement. Resurfacing is used when the pavement has medium to high levels of distress, which would make the use of CPR techniques too expensive or less reliable.
Concrete overlays fall into two basic categories: concrete overlays for concrete pavements and concrete overlays for asphalt pavements. Within each of these categories are two overlay types, bonded and unbonded.
Concrete Overlays of Concrete Pavement
Bonded concrete overlays of concrete pavements are primarily used to increase pavement structural capacity. They consist of a thin concrete layer (4 inches or less) bonded to the top of the existing concrete surface to form a monolithic or composite section. Typically, pavements that have very little deterioration, but are too thin for an increasing traffic volume, are good candidates for a bonded overlay. Bonded concrete overlays are not recommended when the existing pavement is badly deteriorated and a substantial amount of removal and replacement of existing layers is necessary during rehabilitation. Bonded concrete overlays are also not appropriate if there is significant deterioration of the existing pavement from a material durability problem like "D" cracking or alkali-silica reaction.
Unbonded concrete overlays consist of a relatively thick concrete layer (5 inches or greater) on top of an existing concrete pavement. Unbonded overlays are generally most cost effective when an existing concrete pavement is badly deteriorated and removal of existing pavement layers is not desirable. Unbonded overlays react structurally as if built on a strong, non-erodable base course.
Unbonded overlays do not require much pre-overlay repair before placement because of a separating layer used between the overlay and old pavement. The separation interlayer is usually a thin asphalt layer of about 0.5-1.5 inches thick. The layer is sometimes called a debonding layer or stress relief layer. The purpose of the interlayer is to separate the old and new layers so that they may act independently of each other through temperature cycles and load deflection. The separation interlayer prevents distresses in the old pavement from reflecting through into the overlay.
Unbonded concrete overlays are a much better option for deteriorated concrete pavements than rubblization and an asphalt overlay.
Concrete Overlays of Asphalt Pavement
Conventional Whitetopping and ultra-thin whitetopping (UTW) are overlays for existing asphalt pavement. Conventional whitetopping consists of a thick concrete layer (4 inches or more) on top of an existing asphalt pavement. When loaded by vehicles, the new overlay behaves just like a new concrete pavement on a strong base course.
Whitetopping overlays are effective for almost all applications. They have been successfully used on interstate highways, state primary and secondary roads, intersections, etc. as well as major airport and general aviation runways, taxiways, and aprons.
Conventional whitetopping offers several advantages. First, they require minimal pre-overlay repair because of concrete's ability to bridge deterioration. Second, the existing asphalt makes an excellent base course with the same advantages of other stabilized base materials -- reduced potential for pumping, faulting, and loss of support.
An Ultra-thin Whitetopping Overlay (UTW) is a thin concrete overlay; 2 to 4 inches thick, placed on top of a prepared surface of an existing asphalt pavement. In addition to being thinner, two other factors differentiate UTW from conventional whitetopping:
- Bonding or partial bonding between the concrete overlay and the existing asphalt pavement
- Very short joint spacing compared to normal (2 to 6 ft instead of 12 to 18 ft).
Bonding the concrete overlay to the asphalt pavement creates a composite section in which the load is shared between the concrete and existing asphalt. The closer joint spacing allows the slabs to deflect instead of bend. This reduces load stresses in the slabs to reasonable values even at thickness of just 2 inches.
UTW is applied where a substantial thickness of asphalt exists, such as full-depth asphalt pavements (asphalt surface on asphalt base). UTW is good application for normal traffic loads on residential streets and low-volume roads. Other applications include asphalt intersections where rutting and washboarding is a problem, general aviation pavements, and parking areas. Many projects have been fast-tracked and opened to traffic quickly.
Click here to design a UTW pavement! (this link accesses the UTW Load-Carrying Capacity Calculator, which can be used to estimate the life of a UTW pavement)
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