A Functionally Optimized Hot-mix Asphalt Wearing Course: Part I: Preliminary Results

About the report:

The purpose of this report was to highlight the preliminary findings of the design, production, placement, and early life performance of a new generation open-graded surface course (also referred to as porous friction course [PFC]) for use in Virginia. The primary objective of the larger research project is the design of a functionally optimized hot-mix asphalt wearing course. This report documents important aspects of the mix design and construction and the initial functional quality of the new surface. General observations associated with the trial section and normal production and placement activities are accompanied by a summary of the quality characteristics of the material. Special emphasis is placed on the very early life functional characteristics of the new wearing course. Among these key characteristics are ride quality, skid resistance, and tire-pavement noise. Observations made during trial production and placement led to "lighter" recommended application rates and reduced temperatures. Preliminary functional tests indicated that the PFC is exhibiting exceptional early-age skid resistance, incentive-quality smoothness, and low tire-pavement noise. On the basis of initial cost and early-life functional performance, the PFC is cost-competitive with traditional mixes placed at traditional application rates (when those mixes are used for functional rather than structural improvement). The report includes (as an appendix) a revised special provision for PFC that incorporates the recommendations pertaining to mix production and placement. It encourages Virginia Department of Transportation pavement engineers to consider a PFC when lower noise, exceptional skid resistance, and good ride quality are desired and additional structure is not necessary. However, it also cautions against widespread application of the technology until at least a final report on performance can be issued. The projected completion date for this report is winter 2010. In the absence of long-term performance data, the costs and benefits assessment is focused on initial costs and initial performance criteria. As a wearing course only, the PFC is $0.28 per square yard cheaper than a comparable dense-graded mix ($5.08 versus $5.36) if both mixes are placed at the normally recommended application rates. The PFC further offers the quantified benefits of much greater skid resistance and noticeably lower noise production. The additional advantages of reduced splash and spray are acknowledged but not quantified.

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