The Effect of Loading Level and Rate in the Indirect Tensile Test

This paper investigates the effect of loading level and loading rate on the damage development and strength on the asphalt mixtures tested at three low temperatures. The current AASHTO specification for asphalt mixture low-temperature characterization consists of two tests: the indirect tensile creep (ITC) test and the indirect tensile strength (ITS). In the ITC, the load was applied until the horizontal deformation on one face reached 0.00125 mm to 0.019 mm and then was held constant for 1,000 seconds. In the ITS, a constant loading rate was maintained until failure. In this study, different loading levels were used in the creep tests: 25% to 60% of the peak load observed in the strength test. Three different loading rates were employed to perform the ITS test at all tested temperatures. The experimental results show that test temperature has a significant effect on the behavior of the material. Data analysis from the creep test indicates that significant damage develops when the loading level during creep reaches more than 55% of the material strength. Analysis of the strength test data illustrates that the loading rate significantly affects the response of the material. For each test temperature, asphalt mixtures have lower peak loads and larger displacements when tested at a lower rate. The measured tensile strength value significantly increases with the increase of the loading rate.