Evaluation of Trapezoidal Shaped Grooves
As with the NAPTF, ACY, and MCAF Quantico groove installations, the only noticeable difference with the installation activity was the time it took for the contractor to change the cutting blades on the groove-cutting machine when it was time to switch to a different groove pattern. As mentioned, this step would normally not occur in the real installation as the contractor would not be switching between the standard and trapezoidal blades. The airport operations staff at ORD reported no noticeable differences in the installation process involving the trapezoidal-shaped grooves. As with the MCAF Quantico installation, the complexity of the test layout required the contractor to spend some time measuring the runway to ensure that the sequence and size of the test sections were correct. This, of course, would not be a factor in a real-world installation. The operation resumed without any unexpected issues. It was estimated that the contractor was able to groove the asphalt pavement at a rate of approximately 28 linear ft (by 9 3/8 ft wide) per minute, which is comparable to the rate for cutting standard grooves in asphalt. Cost. Another objective of Phase Four was to compare the cost differences associated in cutting trapezoidal-shaped grooves versus standard groove cutting in asphalt pavement. For the installation at ORD in early 2008, the costs for cutting the trapezoidal-shaped grooves averaged $1.50 per square yard, not including transportation and material costs. Comparably, the cost for cutting standard grooves would have cost approximately $1.10 per square yard. As noted, the cost for cutting the trapezoidal-shaped grooves would be about 15% to 25% higher than the standard grooves until the cost of the blades decreases with the growth of large-scale production. Local labor rates, work hours, and other site-specific factors can also affect pricing. Wear And Durability. Researchers monitored the trapezoidal-shaped and standard groove areas to observe differences in wear and durability. Specifically, they were watching to see how the grooves endured over a long term, maintained their specified shape, and resisted rubber contamination. Approximately 10 months after the groove installation was completed at ORD, researchers returned to the airport to conduct their first evaluation. It was noted that there was a difference in the amount of rubber contamination on the trapezoidal-shaped grooves, just as was observed at MCAF Quantico. Researchers noticed that there was less rubber buildup on the top edges of the trapezoidal-shaped grooves than there was on the top edges of the standard groove. Figure 46 shows a portion of the runway at ORD where the grooves transition from standard to trapezoidal. Note the additional rubber contamination on the standard grooves on the left, versus the trapezoidal-shaped grooves on the right.
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