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Use of Viscosity Standard Fluid To Control Quality of Rheological Measurements for Characterizing Asphalt Binders

The results of a study to establish a protocol for calibrating and maintaining Superpave rheometers are described. The reference standard material used was supplied by Cannon Instrument Co. The material (high viscosity standard) is designated as N2700000 and is supplied with ASTM traceable values of steady shear viscosity at various Superpave specification temperatures. The main objective was to determine whether sound calibration practices and adequate training can improve the repeatability and reproducibility of the rheological parameters required in the Superpave binder specification. Ten laboratories participated in the study. The results indicate that the viscosity standard can be used as a standard fluid to calibrate and maintain the Superpave rheometers. The repeatability and reproducibility data were compared with similar estimates reported by the AASHTO Materials Reference Laboratory. It was found that the reproducibility (between-laboratory variation) improved by a factor of two and repeatability (within-laboratory variation) improved modestly. With these results, a protocol for using the standard was also developed. Further analysis of results is under way to determine the frequency of calibration and maintenance required to obtain consistent rheological measurements. The results of this analysis and efforts to implement statistical process control charts for calibration and maintenance of rheometers using the standard reference fluid (Cannon N2700000 viscosity standard) are discussed.