Forensic Laboratory Tests to Evaluate Long-Term Performance of Reclaimed Asphalt Pavements: Connecticut Case Study

Abstract

This paper presents the most significant findings from the forensic evaluation of the long-term cracking performance of asphalt mix designs including Marshall and Superpave mixes with various performance grades of binders and RAP content of 25% total weight of aggregates. The experiment targeted comparison of permeability, stiffness, low-temperature behavior, and oxidation susceptibility of the mixes and correlation of those properties with deflection and cracking data from the six LTPP SPS-9A sections on Route 2 in Connecticut. The mechanical testing in the laboratory included measuring hydraulic conductivity by a Flexible Wall Permeameter, dynamic complex modulus by the Asphalt Mixture Performance Tester (AMPT), creep compliance and tensile strength by Indirect Tension Test, and fracture properties by Semi-Circular Beam (SCB) test. The evaluation of field performance included analysis of deflection basins and back-calculated elastic moduli from Falling Weight Deflectometer data as well as visual evaluation of surface distresses, such as cracking and weathering. The forensic laboratory testing revealed reasonable correlations between some laboratory test results and field performance. For instance, the dynamic modulus values measured by AMPT at 20 C at the highest and lowest frequency were found to be similar to the backcalculated asphalt layer moduli. The extent of transverse cracking appeared to be highly associated with the Young moduli estimated from SCB fracture energy and toughness. The amount of longitudinal wheelpath cracking correlated better with SCB fracture energy. On the other hand, neither fracture properties nor tensile strength was found to be correlated with the extent of longitudinal joint cracking observed. The laboratory testing revealed overall higher stiffness and oxidation in RAP-containing mixes. The use of those stiffer mixes, however, did not affect much load-related performance of the experimental pavement sections. On the other hand, a very fast deterioration of longitudinal joints occurred in all pavement sections, which was found most likely related to creating cold joints during paving. This phenomenon has been reduced in current practice with the introduction of wedge joints by the CTDOT.