Development of the Thickness Design for Concrete Pavement Overlays over Existing Asphalt Pavement Structures

Several thin whitetopping (TWT) projects in the U.S. were reviewed to identify variables with significant effects on TWT behavior and performance. The joint spacing has a significant effect on performance as it determines the wheel loading condition in the slabs. Joints placed under or near the wheel paths caused serious distresses in TWT due to corner loading condition. Full-scale whitetopping pavement was constructed and tested under static and constant cyclic loading for fatigue. The concept of equivalent fatigue life was applied to correct the effect of the different stress ratios. The S-N curve developed from this study was very close to Thompson and Barenburg’s S-N curve after the application of the equivalent fatigue life concept. A factorial experiment was developed that included almost all the variables related to TWT designs. A total of 7,776 treatments were identified. Computer program ISLAB2000 was selected as an analysis tool, as it was used in the development of the Mechanistic-Empirical Pavement Design Guide (MEPDG). ISLAB2000 was run 7,776 times and the results were statistically analyzed. Using log-log regression, the analysis results were approximated with the generalized English unit design equation for the determination of the required whitetopping thickness with several conservative assumptions. Current Texas Department of Transportation (TxDOT) design method for TWT does not account for the condition of the existing hot mix asphalt pavement. Rather, the slab thickness is determined solely by the future truck traffic. In addition, current TxDOT design method for TWT requires truck traffic as input while TP&P provides traffic information in terms of equivalent single axle loads (ESALs). The proposed design equation is more realistic in that it accounts for all the design variables including layer characteristics. It also utilizes ESAL as traffic input. Therefore, the proposed design equation will provide TxDOT engineers with more accurate and convenient design tool for TWT.

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