By: Gerald F. Voigt, P.E., Contributing Author
The concrete pavement industry is setting the record straight on the misconception that concrete is too difficult to rehabilitate. Outreach and educational information from the American Concrete Pavement Association (ACPA) is going a long way in educating agencies and consultants about the best ways to rehabilitate distressed pavements using concrete.
These efforts are aimed at dispelling myths and misinformation that can represent a huge drain on an agency’s resources. For example, we have observed flexible overlays placed over concrete pavements that are still structurally sound, but perhaps need only restoration or resurfacing. Equally disconcerting are the cases when structurally sound concrete pavements have been destroyed prematurely and either resurfaced or reconstructed with flexible materials because better alternatives were never considered.
The concrete pavement industry supports a “mix of fixes,” a number of rehabilitation methods that address both short- and long-term requirements. The concept behind a mix of fixes is that sound planning and pavement assessment will not only help address pavement performance issues as early as possible, but also will help select the right corrective action.
The concrete pavement industry offers a wide variety of pavement renewal solutions, including: concrete pavement maintenance, restoration (CPR), resurfacing and reconstruction techniques. In general, selecting the right option depends on the current conditions of the pavement, traffic requirements, required design life and the relative life-cycle costs.
The most common type of concrete pavement maintenance is joint re-sealing, which also fits into the industry’s broad strategy known as concrete pavement restoration, CPR, a series of engineered procedures used to manage the rate of concrete pavement deterioration.
The first type of rehabilitation procedure applied to concrete pavement ideally is CPR, which is used when the pavement exhibits only slight deterioration. CPR techniques fall into a number of subcategories, which may not all be required during the life of a pavement, but should be followed in the appropriate order. They also may be either preventive measures or corrective techniques.
Applying the right CPR technique requires identification and classification of distresses, noting whether they are structural (which affect the pavement’s ability to carry traffic) or functional (which may affect ride quality and safety, but do not impact the pavement’s load-carrying capability). Examples of structural distresses include cracking or joint deterioration, while functional distresses include roughness or surface polishing.
Concrete pavement resurfacing using overlays is indicated when pavement has medium to high levels of distress and restoration would not be expected to perform effectively.
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.
Two concrete overlay technologies that have been developed and refined over the years are conventional whitetopping and ultra-thin whitetopping (UTW).
Conventional whitetopping consists of a thick concrete layer (4 in. or more) on top of an existing asphalt pavement. When loaded by vehicles, the new overlay performs 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, as well as other roadways, intersections and airport pavements.
UTW is a thin concrete overlay; 2 to 4 in. thick placed on top of a prepared surface of an existing asphalt pavement. In addition to being thinner, they differ from conventional whitetopping because they are bonded or partially bonded to the existing asphalt pavement and feature short joint spacings (2 to 6 ft versus 12 to 15 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 in.
Both whitetopping and UTW are designed for existing asphalt surfaces. Standard whitetopping and UTW have well-deserved track records as inexpensive, quick, cost-effective and durable ways to eliminate the constant maintenance and frequent repairs of problems.
Pavement reconstruction, the total removal and replacement of worn out or insufficient pavement, is used when the pavement has high levels of distress, when overlays will not solve the problem or when the pavement has simply outlived its design life.
There are many factors to consider prior to reconstruction, but one of the most significant is cost. With the increasing demands on America’s highways, it is important to evaluate more than the initial costs, but also consider what the pavement will cost during its entire design life.
About The Author: Voigt is senior vice president - technical services and chief operating officer for the American Concrete Pavement Association, Skokie, Ill.
