Evaluation of Trapezoidal Shaped Grooves

All construction operations were completed within one workday. After the cutting operation was complete, molds were taken of the untrafficked trapezoidal-shaped grooves. A forensic evidence collection kit typically used by law enforcement for capturing accurate positive molds of tire tracks and footprints was used. The plaster is specially formulated to cure rapidly without expansion or shrinkage. Figure 16 is a photograph of one of the molds.

Figure 16. Plaster Mold of Trapezoidal-Shaped Groove The contractor cutting the trapezoidal-shaped grooves stated that he was able to maintain similar inspection and acceptance tolerances to those that are in place for standard grooves. The tolerances were as follows: depth of the groove was 1/4 in.,  1/16 in., the width of the top of the groove was 1/2 in.,  1/16 in., the width of the bottom of the groove 1/4 in.,  1/16 in., and the spacing between groove centers 2 1/4 in., +0/-1/8 in. THE NAPTF TEST DESCRIPTION. The pavement in which the test grooves were installed was trafficked with a four-wheel dual-tandem configuration on both north and south traffic lanes. The geometry was the same on both traffic lanes, with dual spacing of 54 in. (137.2 cm) and tandem spacing of 57 in. (144.8 cm). Wheel load was set at 55,000 lb (25 tonnes). Trafficking started on July 7, 2005, and continued until October 6, 2005, following the schedule in table 1. (The loading was increased after 5082 repetitions, because none of the pavements showed any significant deterioration at that traffic level.) The standard NAPTF 66-repetition- per-cycle wander pattern was used on both traffic lanes. The temperature of the asphalt varied between 66° and 85°F (19° and 29°C) during the test period. The average temperature of the asphalt was about 78ºF (26°C).


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