Fracture and Strength Tests for Airfield Balance Mix Design

Abstract: Asphalt concrete (AC) is a common construction material, comprising of stiff elastic aggregates bound by a softer viscoelastic asphalt binder matrix. Majority of airfield runways and taxiways are constructed with AC due to its cost-effectiveness, ease of construction and desirable surface characteristics. To improve airfield sustainability resiliency, focus has shifted to implementing performance tests during the design of AC mixes. Cracking is one of the predominant modes of failure in airfield pavements. However, the current Federal Aviation Authority (FAA) standards lack any performance tests to predict cracking potential of AC mixes during the design. This study focused on characterizing the cracking potential for eight different AC mixes, obtained from airports across the United States. The Illinois Flexibility Index Test (I-FIT) and Cracking Tolerance Index Test (CTI) were used to predict AC cracking potential due to their ease of implementation and high rate of adoption in the country. Impact of both the aggregate properties (size, lithology, skeleton structure) and asphalt binder characteristics (performance grade, modification) on I-FIT and CTI results was investigated. Both plant-mix lab-compacted and lab-mix lab-compacted specimens were tested to quantify the field compaction effect. Digital image correlation was utilized to monitor crack initiation and propagation during testing. The difference between fracture and strength tests was presented. The study proposes thresholds to control cracking potential of AC mixes. Samples were collected from the accelerated loading tests at the FAA facility in New Jersey for validation of the proposed thresholds.