Initial Validation of Balanced Mix Design Performance Test Thresholds Through Laboratory,Field,and Accelerated Testing

Abstract

Validation of balanced mix design (BMD) test thresholds is essential for building confidence in performance-based asphalt mix designs. To support Texas’ BMD implementation, multiple field test sections statewide have been monitored, accumulating data from preconstruction through several years of service. These sections, exposed to traffic levels ranging from 600 to 23,000 average annual daily traffic (AADT) and up to 1.0 million equivalent single-axle loads (MESALs), provide valuable insights into test thresholds across diverse traffic and regional conditions. Complementary data from three national center for asphalt technology test track sections subjected to accelerated loading compare traditional volumetric designs and BMD specifications. Additionally, materials from the original WesTrack test track were evaluated with current cracking and rutting tests to relate historical field performance with present protocols. Despite challenges in collecting long-term field data and variability from traffic and environmental factors, key conclusions emerged. The indirect tensile asphalt cracking test and Texas overlay tester effectively gauge cracking resistance differences among mixtures, correlating well with field outcomes. The Hamburg wheel tracking (HWT) test reliably identifies mixtures prone to rutting, supported by minimal rutting observed in TxDOT sections. The IDEAL-rutting test (IDEAL-RT) consistently differentiates rutting resistance and predicts field rutting performance, underscoring its value in mix design. Early reflection cracking observed within two years exhibited strong correlation with the cracking tolerance index (CT Index), indicating higher CT Index values improve cracking resistance. Gradation also significantly influences CT Index and crack progression rate (CPR) results, emphasizing the need to incorporate gradation-specific thresholds. These findings enhance understanding of BMD test strengths and limitations, informing refinements aimed at improving pavement durability statewide.