Variability of Asphalt Mixture Tests Using Superpave Shear Tester Repeated Shear at Constant Height Test

Analyses were conducted on data obtained from the Superpave shear tester using the repeated shear at constant height (RSCH) test. The data indicated that even under the most controlled experimental conditions, the resulting parameters showed high variability. Up to six replicate samples were tested using an extra shear linear variable differential transformer. The coefficient of variation of the permanent strain at 5,000 load cycles for six samples was between 10 and 20 percent in most cases. From the different options studied to decrease variability, the trimmed-mean method provided the greatest decrease in the coefficient of variation without affecting the mean of the results. In this method, five specimens are tested, the high and low values eliminated, and the remaining three are used to obtain the mean and standard deviation of the results. Since the suggested trimmed-mean method requires an increase in the number of samples tested to five, it is proposed that the number of load cycles used in the RSCH test be reduced for materials placed in low-volume roads.