Impact of Price Reductions on the Long-Tern Pavement Performance of HMA Mixes in North Carolina

Article 105-3 of the North Carolina Department of Transportation (NCDOT) Standard Specifications for Road and Structures provides guidance on price adjustments for hot mix asphalt (HMA) pavements that are not within reasonably close conformity with the specifications but for which the work is to be accepted and remains in place. Although the impact of this Article is enormous, no research has been done in North Carolina to support whether the current practice is adequate. The primary objective of the research reported herein was to determine whether price reduction calculations under the provisions of Article 105-3 are adequate. The type of pavement deficiency addressed in this research is in situ density. Both fatigue and rutting performance are evaluated. The following laboratory tests were performed on two North Carolina Superpave mixtures with varying air void contents: (1) axial compression dynamic modulus tests for modulus determination; (2) indirect tension (IDT) tests for fatigue performance evaluation; (3) triaxial repeated load permanent deformation (TRLPD) tests for rutting evaluation; and (4) accelerated pavement tests on laboratory pavement slabs for fatigue and rutting evaluation using the third-scale Model Mobile Loading Simulator (MMLS3). Air void models for the dynamic modulus, fatigue cracking, and rutting are developed using the laboratory test data. The results from the material level performance tests and the MMLS3 tests allowed the calculation of the price reduction factor (PRF) values. It was found that the PRF values are not sensitive to the testing methodology used (i.e., the MMLS3 vs. IDT or TRLPD tests); rather they are significantly different, depending upon which performance characteristic is used (i.e., fatigue cracking vs. rutting). Pavement performance prediction methodologies were developed that predict the fatigue life and permanent deformation growth of the asphalt pavement under the MMLS3 loading. These methodologies are based on material level performance models, multilayered elastic analysis, and the time-temperature superposition principle to account for the differences between the material level testing conditions and the MMLS3 testing conditions. The fatigue life prediction algorithm adopts a cumulative damage analysis; the permanent deformation prediction algorithm uses a sublayering method. It was found that the prediction methodologies yield reasonable predictions of fatigue life and permanent deformation growth of asphalt slabs under the MMLS3 loading. These pavement performance prediction methodologies were implemented into the computer program called AP4 (Asphalt Pavement Performance Prediction Program). This program allows the determination of the service life for fatigue cracking and rutting based on the inputs of air void contents in all the HMA layers. Case studies of five density deficient pavements were conducted, which resulted in reasonable price reductions.