Effect of Parallel Plate Gap Height on Repeatability in DSR Measurements of Crumb-Rubber Modified Binders

Abstract

Current Superpave performance grade (PG) grading specification utilizes a dynamic shear rheometer (DSR) at a gap height of 1-mm to determine the high-temperature performance grade of asphalt binders. It has been anticipated that rubber particulates greater than 25% of the gap height may interfere with the measurements, resulting in properties that may not represent the actual crumb rubber binder. Therefore, this study tries to adjust the 1-mm gap height for measuring high-temperature performance properties of crumb rubber binders to minimize the effects of interaction between the asphalt binder and rubber particle on PG grading results. Trial gap heights of 2 and 3 mm were used to test five different crumb rubber modified (CRM) binders. The CRM binders were evaluated using the standard Superpave high-temperature grading test and multiple stress creep and recovery (MSCR) test. Results were analyzed using statistical analysis, and through the comparison with single operator precision statements, where it was shown that higher variability is observed at the 2-mm gap height relative to the 3-mm gap height. Also, the repeatability between replicates was deemed acceptable, particularly for the 3-mm testing gap. Based on the results, a parallel plate gap height of 3 mm was recommended, and modified stress levels and testing temperatures for the MSCR test were proposed.