Mix Design, Construction, and Performance of a Thin HMA Overlay on Pumphrey Drive, Fort Worth, TX (5-5123-01-2)

A thin (1 inch-1.5 inch) hot-mix asphalt (HMA) overlay was constructed on Pumphrey Drive in Tarrant County, Fort Worth from July 30, 2007, to August 3, 2007. This report documents the mix design, construction, and field performance of this overlay project. Two Type F mixes were designed for this project following the new proposed balanced mix design procedure. These two mixes had the same original PG64-22 binder, aggregates, and gradation but different binder modifiers. One mix was modified with 7 percent crumb rubber and the other modified with 3 percent SBR latex. After construction, three visual site inspections on this thin overlay project were conducted on December 14, 2007, April 2, 2008, and July 30, 2008. The overall performance of this thin HMA overlay project is very good and has been considered successful by TxDOT and Tarrant County. Almost no rutting was observed on the main traffic lanes, except at a stop condition intersection on the south end of the project. Only a few transverse reflective cracks occurred on the ramps and a few longitudinal cracks occurred on the main traffic lanes. Additionally, the pavement still looks dark after 1 year of being subject to traffic and the sun's UV rays. Some reflective cracking was seen at the on- and off ramps and main traffic lanes but those cracks stayed mostly tightly closed and did not get worse since the first field visit on December 14, 2007. The early reflective cracking on the ramps was due to poor load transfer efficiency at the joints and on the main traffic lanes due to continual differential settlement of the foundation. The cracks were observed in the July 30 visit to be minimized from previous visits. Therefore, these thin overlays are not recommended to be used on any PCC pavements with poor load transfer efficiency (< 70 percent). Otherwise, the early reflective cracking will be a potential problem.