Abstract Manager

Typically, a mixture design for asphalt concrete (AC) is carried out to select a desired combination aggregates and asphalt binder to meet some specified requirements. Marshall and SuperPave (SP) are the two most commonly used methods for AC mix design. In Marshall method, agency specific aggregate gradation and properties, and asphalt mix properties are targeted. Alternatively, SuperPave method provided standard requirements for aggregates and mix properties to ensure durable mixtures with good rutting and cracking resistance under various loading and weather conditions. However, none of these methods, explicitly set limiting criteria and their targets for AC mix field performance in terms of rutting, fatigue cracking, thermal cracking, resistance to moisture related stripping, etc. The BMD approach attempts to make a good balance between field performance and mix constituents, which is an important step as highway agencies and asphalt mix producers are making continued efforts to improve sustainability, particularly with the use of recycled asphalt materials, polymer modified asphalt binder and antistripping agents. The BMD uses several performance tests, to address key distresses in pavement, including Hamburg Wheel Track Test (HWTT) for rutting and moisture stripping, Flexibility Index Test (I-FIT) or Indirect Tensile Cracking Test (CT index) for fatigue cracking potential and Fracture Energy of Asphalt Mixtures Using the Semicircular Bend Geometry (SCB) for thermal cracking resistance. The objectives of this study are to characterize Manitoba’s AC mixes and set minimum requirements to achieve durable and sustainable pavement structures.

24 AC mix samples have been collected from different project sites, and HWTT,  I-FIT, Ideal-CT, SCB-Fracture Energy and resilient modulus testing have been completed or expected to be completed shortly. These mixes include Bit. B (a Marshall mix), SP12.5 and SP19.0 with aggregates from different sources across the province, different traffic categories for SP mixes, different asphalt binder grades, RAP and RAS. Preliminary assessment of results showed that all tested mixes met the maximum 12.5mm rutting target. SP mixes met the rutting criteria even at 50 °C. Mixes with polymer modified binder met the fatigue cracking target (FI of 8 -15) and standard PG-34 did not meet this target FI. The results of Ideal-CT test seem to be inconsistent. All mixes met the thermal cracking criteria (fracture energy of 900-1500 J/m² at -36 °C). This paper will present the details of the various tests, test matrix, results and recommendations, which could enhance knowledge of interested highway agencies and other entities.