Field Shear Test for Hot Mix Asphalt

This digest summarizes key results of National Cooperative Highway Research Program (NCHRP) Project 9-18, "Field Shear Test for Hot Mix Asphalt." Of particular interest is the description of the redesign of the field shear test (FST) device which was developed as a potential quality control and quality assurance (QC/QA) tool. The redesigned FST was found capable of performing a variety of tests, but the best results were obtained from the frequency sweep procedure described in American Association of State Highway and Transportation Officials (AASHTO) TP7 at high temperatures and high frequencies. Under these conditions, the equipment produced dynamic modulus values and phase angles in the same range as those generated using the full-sized Superpave shear test equipment described in AASHTO TP7; moreover, these results were found to be fairly sensitive to changes in hot mix asphalt (HMA) composition. However, while the data repeatability of the redesigned FST is similar to other methods for measuring HMA stiffness, it remains too high for QC/QA testing.