Several test methods are in practice to assess the rutting potential of a mixture. The commonly used procedures are Diametral tests, Uniaxial test, Triaxial tests, Shear tests, Empirical tests, and Simulative tests. Of all these test methods, simulative test methods are relatively easier to use and ready for immediate adoption. The APA test is the most widely used simulative test. It is imperative that the rut depth criteria for the APA test should be developed for its employment. In a recent study conducted at NCSU, it was concluded that the APA could clearly detect poorly performing mixtures. With the limited availability of data, a reasonable correlation was observed between the APA tests and Repeated Shear at Constant Height (RSCH) tests. In view of this, a comprehensive research study should be conducted on all the surface mixtures used in North Carolina to develop the rut depth criteria. The rut depths measured from the APA tests would be compared with the corresponding shear strains of the RSCH test. Statistical analysis would be performed on the test results as measured by the APA and the RSCH tests. In addition, the APA test would be fine-tuned by addressing many issues related to air voids, test temperatures, gradations and aggregate sources. The correlations estimated using the data obtained from the APA and Shear tests would be used to develop rut depth criteria for the APA test. The developed rut depth criteria for the APA test could be adopted for immediate use in practice.
The primary objectives of this research study will be to:
- Conduct APA and Shear tests on all the surface course mixtures used by the NCDOT.
- Develop correlations of Shear tests and APA test data.Fine-tune the APA test by considering different air voids, test temperatures and aggregate sources and quantify the effect of these variables on the predictability of the APA.Develop and recommend the APA test criteria for evaluation of rutting potential of the mixtures.
- The proposed study will provide a simple and effective methodology and design criteria for using APA for Superpave surface mixtures. The rut depth criteria could be implemented for all the new surface mix designs and test contractor submitted specimens for compliance. The implementation would result in better overall pavement performance and possibly less rutting in HMA pavements in North Carolina.