Evaluation of In-Situ Shear Stiffness of Asphalt Concrete Mixtures

In cooperation with the Ontario Ministry of Transportation and the United States Transportation Research Board, researchers at Carleton University in Ottawa, Canada have developed the InSitu Shear Stiffness Test (InSiSST) – a new field test facility for measuring shear stiffness of compacted asphalt concrete surface layers. To date, various field-testing programs have been conducted to evaluate the in-situ shear stiffness of asphalt concrete mixes using the newly developed InSiSST. In this paper, a brief overview of the InSiSST facility is presented, together with the results of testing completed in Ottawa, Bancroft, Toronto, and at the Long Term Pavement Performance (LTPP) SPS-9A test site located in Petawawa, Ontario. The Petawawa site (870900) is of particular interest as four of the six test sections consist of SuperPave asphalt mixes, while the remaining two sections were designed using the Marshall method. The results of field testing at these locations has indicated that the InSiSST is both sensitive to differences in asphalt mix shear stiffness and is able to rank mix performance between different mixes in terms of measured permanent deformation. With continued refinement and testing, is expected that InSiSST will become a valuable test facility for the design and quality control of hot mix asphalt concrete pavements.