The objectives of this project were to (1) enhance and refine the field shear test (FST) device and procedure for quality control and quality assurance (QC/QA) of the production and lay down of hot mix asphalt (HMA) developed in NCHRP Project 9-7; (2) validate the effectiveness of the FST method in field QC/QA and as a mix design tool for predicting the susceptibility of HMA to permanent deformation in service; and (3) facilitate the implementation of the FST as a standard method in field QC/QA and in mix design.
The FST device was redesigned to improve its test configuration and increase the precision of its measurements. 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 AASHTO T 320 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 T 320; moreover, these results were found to be fairly sensitive to changes in asphalt concrete composition. However, while the data repeatability of the redesigned FST is similar to other methods for measuring asphalt concrete stiffness, it remains too high for QC/QA testing.
Follow-up Project 9-18(01) evaluated the sensitivity of complex modulus measurements made with the redesigned field shear test (FST), following a new and potentially more effective testing protocol. The results suggest that the FST device is a precise, sensitive tool for measuring the complex modulus of HMA.
The final report for Project 9-18 has been published as NCHRP Research Results Digest 262
The final report for Project 9-18(1) has been published as NCHRP Web Document 56