No abstract

Many agencies place hot-mix asphalt overlays on deteriorating jointed or cracked portland cement concrete pavements to improve the ride, protect the pavement structure, and reduce noise. Reflection cracking of the joints and preexisting cracks through the overlay is a persistent problem. In climates such as that in Wisconsin, the initial reflective cracks often appear within a year or two. The Wisconsin Department of Transportation and the City of Milwaukee tried a fine-aggregate, asphalt-rich, polymer-modified asphalt mix interlayer to absorb joint movements, delay reflective cracking, and protect the existing pavement. Four Wisconsin projects are discussed. In the first project, constructed in 1996, the interlayer showed no effect on delaying reflection cracking within the first 3 years. Later projects, however, included specifications for performance-related design tests for flexural beam fatigue and Hveem stability and were overlaid with improved mixtures to complement the flexible interlayer. The later projects showed an average 42% improvement in the time to the appearance of surface cracks compared with the control sections. Furthermore, cores taken from the projects showed that even when the overlay cracked, some of the interlayer samples did not, even under severe conditions, thus further protecting the underlying pavement structure. Other major factors contributing to the cracking delay included the type of concrete pavement, concrete patches, and climate.