Asphalt overlays are one of the most common tools for rehabilitating existing asphalt and concrete pavements. However, the performance of new overlays is often jeopardized by the cracking distress in the existing pavement. This existing cracking propagates, or reflects, through the new overlay to the surface of the new overlay. The rate at which this reflection cracking propagates to the surface is a function of overlay thickness crack severity, traffic loading and subgrade or subbase support. Reducing the rate at which these reflection cracks propagate to the surface of the pavement is desirable in order to lengthen the time between rehabilitation projects or crack sealing operations.
The use of vibratory steel rollers during breakdown compaction of hot mix asphalt overlays on asphalt pavements containing crack sealants appears to exacerbate the presence of bumps and transverse cracks in the new asphalt directly over and in front of the cracks. the new asphalt directly over and in front of the cracks.
This final report is intended to provide information regarding the performance of crack sealants supplied and installed by three manufacturers for experimental use in a three-year evaluation of in-service pavements on three Colorado highways.
This report analyzes the quality control/quality assurance (QC/QA) data for hot mix asphalt (HMA) using voids acceptance as the testing criteria awarded in the years 2000 through 2010. Analysis of the overall performance of the projects is accomplished by reviewing the Calculated Pay Factor Composite (CPFC) and Incentive/Disincentive Payments (I/DP). Analysis of each of the elements: asphalt content, voids in mineral aggregate (VMA), air voids, mat density, and joint density is presented in tables, figures, and reports. Various data groupings are used to evaluate the data including: year, region, and grading. The specification and the projects are performing reasonably well. The results for the data show that quality of the projects is remaining fairly consistent. No definite upward or downward trends can be seen in the data. Over the eleven-year time period more projects have received incentive payments than disincentive payments. The average CPFC over the eleven years evaluation is 1.00569. The quality levels in the individual elements are at relatively high levels. The VMA and mat density elements show the best results being above 93 percent within the specification limits. The asphalt content and air voids elements are at approximately 90 percent. The joint density pay factor is under 1.0 but is expected to rise as contractors gain experience in this area.
Colorado Department of Transportation (CDOT) has dynamic modulus (E*), and flow number (N) database of different mixes from different regions of Colorado. The sensitivities of these mixes considering factors such as mix types, aggregates source, volumetric properties, contractors, preparation times, binders, etc. on E*, and N, and on the pavement performances are investigated in this study.
Crack sealants are often utilized as a preservation tool in asphalt pavements. When a hot mix asphalt overlay is placed on top a pavement containing crack sealants, a bump and additional transverse cracks sometimes occur in the new asphalt overlay. These bumps and sometimes, transverse cracks are initiated during breakdown rolling and become progressively more severe upon further compaction. This paper presents results of a five-year study designed to identify factors that relate to the appearance of these bumps and consequent cracks.
