Optimized Laboratory Fabrication of Small-Specimen Geometry for Streamlining Dynamic Modulus and Cyclic Fatigue Testing of Asphalt Mixtures

Abstract

The asphalt community is focused on the paradigm shift in mixture design from the volumetrics to an optimization procedure based on performance testing called balanced mixture design. Streamlining performance testing to obtain index properties quickly and using a smaller quantity of materials is critical for the successful implementation. This paper aims to streamline dynamic modulus (|E*|) and cyclic fatigue testing by optimizing the number of 38 mm diameter specimens extracted from a single 150 mm diameter Superpave gyratory-compacted (SGC) specimen. The current provisional standard methods require vertical coring of four small specimens from a single SGC specimen. In this study, two sets of testing specimens were fabricated by coring four and five small specimens from each SGC specimen. The success rate in meeting target air voids, the |E*| analysis, and the cyclic fatigue results including cyclic fatigue index parameter (S_app) values were compared between the two sets of specimens. No significant or consistent differences were observed in performance testing results. Furthermore, innovative image analysis and microscopy techniques were used to study air voids distribution and aggregate structure within each specimen and to further validate the proposed coring pattern. Based on these findings, coring five 38 mm diameter testing specimens from one SGC sample is suggested to run |E*| and cyclic fatigue tests. This proposed modification to AASHTO TP 132 and TP 133 may save technicians’ time and allows for the optimal use of materials. The latter may become a significant saving when integrating these methods with laboratory long-term aging protocols and forensic studies.