The use of digital image correlation for accurate determination of fracture energy density in hot mix asphalt (HMA)

Knowledge of the conditions governing the initiation and propagation of cracks in Hot Mix Asphalt (HMA) mixtures is a prerequisite for a comprehensive understanding of HMA cracking mechanisms. According to the "HMA Fracture Mechanics" pavement cracking model recently developed at the University of Florida, fundamental tensile failure limits of mixtures (fracture energy density and tensile strength) are identified as key parameters in defining the cracking resistance of HMA mixes. A Digital Image Correlation (DIC) system, developed for the purpose of investigating the cracking behavior of HMA mixtures, has been applied to accurately determine fundamental tensile failure limits of SBS polymer modified mixes. The effect of modification on crack localization and crack growth was also investigated. One unmodified and four SBS polymer modified HMA mixes were tested performing both the Superpave IDT test and the Semi-Circular Bending (SCB) test. Tensile failure limits and cracking behavior of two of these mixes (the unmodified and a heavily SBS linear modified) were evaluated also from the Three Point Bending Beam (3PB) test. Full field strain maps indicate that the addition of SBS polymers in mixtures leads to more homogeneous stress states during tensile loading condition, resulting in high strains strongly localized up to the location of impending fracture.