Description
With the growing use of crumb rubber modifier (CRM) as an asphalt modifier there is increased interest in performance based testing versus current testing including viscosity, softening point and penetration. Progress has been made in the past several years using the current Standard Specification for Performance Graded Asphalt Binder (ASTM D 6373 and AASHTO M 320) with modifications. The Dynamic Shear Rheometer (DSR) used for high temperature grading specifies a 1 mm gap. When particulate CRM is present, this narrow gap between the testing plates causes particle on particle interference in the test results. There is an initiative by an AASHTO committee recommending a 2 mm gap for CRM modified binders containing particles 600 micron (30 mesh) and smaller.
The Pacific Coast Conference on Asphalt Specifications (PCCAS) Round Robin Committee has initiated a feasibility study of full Performance Grading (PG) using one CRM modified binder. This paper addresses the Phase One efforts to test CRM binders with particle sizes of 0.6 to 1.4 millimeter (30 – 14 mesh) using existing specifications and a 3 mm gap for both high and intermediate temperatures for DSR. Using ASTM standards for performing inter-laboratory studies has resulted in the data showing strong agreement of variance in inter and intra laboratory data and indicates feasibility of the test method.
