Annotated Literature Review for NCHRP Report 640 (2009)

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206 the current method. An analysis of the normal method of calculating draindown was conducted to compare the two basket mesh sizes. The regression analysis resulted in a R2 of 89 percent. This strong correlation indicates the methods are very comparable to one another. Watson et al mention that since both methods have a good correlation, the only reason to choose one method over another would be the repeatability of test results. The repeatability standard deviation of test results when the 2.36 (No. 8) mesh was used is only 60 percent as much as the standard deviation when the 4.75mm (No. 4) sieve was used. The authors mention that the use of 2.36 mm mesh size provided more repeatable measurements. They explain that probably aggregate particles may have fallen through the 4.75 mm mesh size on some tests but not others. Watson et al also indicate that further evaluation of the ANOVA statistics showed that the addition of fiber stabilizer was the most significant variable contributing to a reduction in draindown. There was as much as 3 percent draindown in specimens prepared without fiber while the addition of 0.4 percent fiber by weight of the total mix resulted in minimal draindown. 1.50.4 Construction Practices No information is provided on construction practices of friction course. 1.50.5 Maintenance Practices No information is provided on maintenance practices of friction course. 1.50.6 Rehabilitation Practices No information is provided on rehabilitation practices of friction course. 1.50.7 Performance No information is provided on performance of friction course. 1.50.8 Structural Design No information is provided on structural design of friction course. 1.50.9 Limitations No information is provided on limitations of use. 1.51 Wimsatt, A. J. and T. Scullion. “Selecting Rehabilitation Strategies for Flexible Pavements in Texas.” TRB 2003 Annual Meeting CD-ROM. Transportation Research Board. National Research Council. Washington, D.C. 2003. 1.51.1 General This paper does not describe any aspect of friction course design or construction, but gives details on observations made during rehabilitation of pavements containing Open Graded Friction Course (OGFC).

207 Wimsatt and Scullion describe the rehabilitation selection strategy that was developed as part of a research project in Texas. They also describe results of case studies of three pavement sections in Fort Worth District in Texas, two which contained OGFC. Only these two are discussed in this review. In the first part of the paper, Wimsatt and Scullion describe a number of procedures for evaluation of pavements and selecting rehabilitation methods. They mention that the TTI Research Report 1712-4, titled “Selecting Rehabilitation Options for Flexible Pavements: Guidelines for Field Investigations” presents an updated summary of the techniques and interpretation guidelines that have been developed by the Texas Transportation Institute over the past two decades in order to conduct an effective investigation. These methods include both nondestructive (Falling weight deflectometer (FWD) and Ground Penetrating radar (GPR)) as well as destructive (Dynamic Cone Penetrometer, DCP) methods. Explanations and equations are provided to describe the use of these techniques. Wimsatt and Scullion then describe the results of three case studies conducted in the Fort Worth District of Texas. Before starting on the discussion about the three case studies, it is necessary to note that TxDOT’s Fort Worth District regularly places seal coats on top of old open graded friction courses. As the authors indicate, the seal coat is used for rehabilitating pavements with substantial rutting distress. For the first case study reported, FWD testing did not reveal any abnormalities in the existing pavements, which had seal coats and patches over OGFCs. However, results of GPR studies indicated entrapment of water in the old OGFC layers. Observation of the cores by TxDOT personnel indicated that the overlying seal coat AC binder did not completely penetrate the open graded friction course, and voids were still present in this layer that could trap water. This was causing the open graded friction course to become unstable due to freeze/thaw cycles during the winter and due to the asphalt stripping from the aggregate in this layer. So, as a result, the upper 51 mm (two inches) needed to be removed. In the second case study, GPR data indicated that the open graded friction courses were holding water where maintenance personnel had placed asphalt overlays. The cores obtained indicated that the open graded friction course layer placed in 1988 was disintegrating, which resulted in the surface distress. Therefore, TxDOT personnel concluded that the open graded friction course layers had to be removed, along with any asphalt overlays on top of those layers. 1.51.2 Benefits of Permeable Asphalt Mixtures No information is provided on benefits of permeable asphalt mixtures. 1.51.3 Materials and Design No information is provided on materials and design of permeable asphalt mixtures.