Evaluation of Practical Asphalt Mixtures Long-Term Aging Protocols for Balanced Mix Design in Quality Assurance Specifications

The Louisiana Department of Transportation and Development (LDOTD) incorporated laboratory performance testing in a balanced mix design (BMD) framework in its 2016 Standard Specifications for Roads and Bridges for all travel-lane mixtures. BMD procedures include loaded wheel tracking (LWT, AASHTO T 324) and semicircular bend (SCB, ASTM D8044) tests for job mix formula approval. However, the 85°C/5 days long-term aging (LTA) requirement for SCB specimens has limited BMD use in quality assurance (QA). Here, practical LTA alternatives were evaluated. Five plant-produced asphalt mixtures were collected. Three LTA levels were selected, following AASHTO R 121: 135°C/6 h, 135°C/8 h, and 120°C/20 h on loose mixtures. Benchmark LTA of 85°C/5 days on compacted samples was also performed. Each mixture was evaluated at the mixture level, supported by binder analysis. Mixture performance was assessed using the LWT test (without LTA) and the SCB test at each LTA level. Asphalt binder was extracted from specimens at each aging level, tested for performance grade, and subjected to frequency sweep testing to evaluate intermediate-temperature cracking behavior. Results indicated that the 135°C/6 h LTA protocol most closely replicated the 85°C/5 days benchmark in both asphalt binder fatigue factor, | G *|·sin(δ), and asphalt mixture SCB cracking resistance parameter ( J _c ), making it a practical alternative for LTA in BMD applications. In contrast, the 135°C/8 h protocol resulted in over-aging of the asphalt binder, while the 120°C/20 h condition produced excessive binder aging relative to the 85°C/5 days benchmark. Normalized performance metrics and statistical analyses further confirmed 135°C/6 h as a suitable and time-saving alternative for use in LDOTD QA specifications.