Very Thin Overlays in Texas

• Thin overlay is a viable option for many maintenance applications.
• Specification requirements and rational for thin overlays are discussed.
• Excellent skid and crack resistances have been observed to date.
• The 25 mm thin overlay costs 30% less than traditional 50 mm overlay.

TxDOT is expanding its use of Very Thin Overlays (VTO) as they are economically viable in resurfacing operations. Currently, the VTO mixes are placed at thicknesses of 25 mm (or less) rather than 50 mm mats and they are 30% less expensive per square yard than the traditional dense graded materials. The thin mats are also ideal in many urban situations and highly desirable for many maintenance applications. This paper summarized the requirements and rational of the specifications that were developed to ensure successful thin overlay projects. To evaluate the performance of VTO mixtures, three field projects were selected and mixtures were designed for each location using local materials. The VTO performance to date has been very good with excellent skid resistance and crack resistance. Like any overlay, the final IRI is impacted by the pre-existing ride, but the typical range of reduction on roughness is about 35–50%. To mitigate low skid and bleeding of existing seal coat, fine PFC option (19 mm) with a high air void of greater than 20% was constructed. The free asphalt did not migrate to the surface and the thin PFC did increase skid resistance by 400% and substantially reduced tire-pavement noise. District staffs are very pleased with the VTO performance to date, more pavement sections have been scheduled to place the same VTO mixes.