Precision Statistics for Frequency Sweep at Constant Height Test (0-1819-2)

A research project, "Evaluation of Shear Strength Property of HMAC for Predicting Performance," was conducted at the Texas Transportation Institute (TTI) with an objective to find the "best" Superpave Shear Test (SST) protocol. Researchers performed a comparative analysis of results from SST and other laboratory-scale rutting tests and recommended frequency sweep at constant height (FSCH) as the "best" SST protocol for predicting rutting of hot mix asphalt (HMA) mixtures. In order to prepare a precision statement for the FSCH, researchers developed and administered an interlaboratory study conducted at the four regional Superpave Centers, Asphalt Institute, and Federal Highway Administration. Three different hot mix asphalt mixtures were tested using the FSCH test at two different temperatures and 10 different frequencies following standard test procedure AASHTO TP7 -01 at each of the six participating laboratories. Before testing, all of the specimens were prepared at TTI. The results were analyzed using both the graphical technique suggested by W. J. Youden and ASTM E 691-99 "Standard Practice for Conducting an Interlaboratory Study." The precision values obtained for the different test parameters were poor due to the high variability of this test procedure.