This proposed research plan aims to complete the Asphalt Mixture Performance Tester (AMPT) tests and performance analysis that were started in the HWY-2017-29 project, evaluate the effects of construction variability on pavement performance using the AMPT tests, IDEAL-CT, and Hamburg wheel-tracking (HWT) test, and verify and potentially improve the acceptance limits and pay factor formulas in the NCDOT's Quality Management System (QMS) manual. The HWY-2017-29 project used a full-depth asphalt pavement on Carr Road in Durham, NC to demonstrate the methodologies used in the FHWA's performance-related specifications. During that project, 27 samples were collected from the RS9.5C, RI19.0C, and RB25.0C mixtures. However, due to limited time and resources, only seven samples from each of the RS9.5C and RI19.0C mixtures were tested. The AMPT test results then were input to FlexPAVETM v. 1.1 to predict the fatigue cracking and rutting performance of pavements.
The North Carolina State University (NCSU) research team developed and verified performance-volumetrics relationships (PVRs) based on the pavement performance predicted by FlexPAVETM. The strength of the PVR approach was demonstrated in the HWY-2017-29 project; however, standard pavement structures were used for the performance simulations instead of the actual full-depth asphalt pavement structure of the Carr Road project. This substitution was necessary due to the lack of an aging model in FlexPAVE™ v. 1.1, which prohibited an accurate evaluation of the effect of surface layer construction variability on pavement performance. Furthermore, the effect of binder content on pavement performance could not be properly represented by the PVRs because a wide range of in-place density in the data that were used to calibrate the PVRs over-rode the effect of a narrow range of binder content. This shortcoming was due to the fact that construction samples instead of specimens fabricated from raw component materials were used to develop the PVRs. In addition to developing PVRs, the NCSU research team developed and verified index-volumetrics relationships (IVRs) using Sapp and the Rutting Strain Index, which respectively are the cracking and rutting index parameters from the AMPT tests, and rut depth from HWT tests. The advantage of the IVR is that it does not involve pavement performance predictions by FlexPAVETM; material-level testing and analysis are sufficient.
In this proposed research project, the NCSU research team will conduct the AMPT performance tests, IDEAL-CTs, and HWT tests using the untested samples from the HWY-2017-29 project, newly acquired mixture samples from the top lift of the surface layer, and laboratory-mixed, laboratory-compacted (LMLC) specimens fabricated from raw component materials. Also, the RS9.5C, RI19.0C, and RB25.0C mixtures will be aged according to the NCHRP 9-54 long-term aging protocol. The aged binder will be recovered using the microextraction and recovery method, and the recovered binder will be subjected to dynamic shear rheometer testing. The aging characteristics of the mixtures will be input to FlexPAVE v. 2.0 to predict pavement performance using the actual Carr Road pavement structural design and the material properties measured from the construction samples and LMLC specimens at 'four corners'. The pavement performance predicted from the four corners and from the construction samples will be used respectively to develop and verify the PVRs and IVRs of the three mixtures. Then, the performance predicted from the PVRs and IVRs and from the measured properties of the construction samples will be used to assess the effects of construction variability on the pavement performance and index values. This assessment will allow the research team to evaluate the current acceptance limits, quality assurance specifications, and pay factor formulas in the NCDOT's QMS manual.
This research will enhance the NCDOT's understanding of the effects of construction variability and the reasonableness of its current acceptance limits and pay factors based on quantitative analysis of pavement performance, thus potentially improving the quality assurance procedure at the NCDOT. The findings also will demonstrate the reasonableness and sensitivity of the study index parameters as a function of volumetric properties and the application of performance-engineered mix design