Design, Construction, and Performance Monitoring of the Very Thin Overlay Placed on Bus 59 in the Lufkin District (5-5598-01-2)

A thin overlay 1-inch thick was placed as a surface layer on the jointed concrete pavement on Business 59 in the Lufkin District. This mix was designed in the laboratory to have a balance of good rut resistance as measured by TxDOT's Hamburg Wheel Tracking test (HWTT) and good reflection cracking resistance as measured by the Overlay Tester (OT). These Crack Attenuating Mixes (CAM) were designed and constructed based on TxDOT's special specification SS 3109. A top quality granite aggregate was used with 1 percent lime and an asphalt content of 8.3 percent with a PG76-22 binder. This project was tested with both Ground Penetrating Radar (GPR) and the Rolling Dynamic Deflectometer (RDD). One area of poor load transfer efficiency (LTE) was noted. The overlay was placed in the summer of 2008. Performance to date has been good. After 1 year some low severity reflection cracks were found in the location where the RDD found poor LTE, and some additional low severity longitudinal cracks were found in one location where the longitudinal joint was directly in the wheel path. The one area of concern with this mix was the relatively low skid values, which averaged around a skid number of 20. A subsequent laboratory evaluation was made of the mix design developed under SS 3109. Using the balanced mix design approach it was found that the HWTT and OT performance criteria were met at binder contents ranging from 7.0 to 8.5 percent. Future applications of this mix should consider reducing the binder content from 8.3 percent to 7.5 percent.