ABSTRACT
ABSTRACT: EN standardisation on asphalt concrete is now enforced in a number of European Countries. Test standards in the EN 12697 series define the methods used to measure mechanical characteristics of asphalt mixes. For a fundamental approach based on modulus and fatigue resistance measurements, frequency and temperature test conditions are specified in EN 13108-1. Because of the fact that there are several tests for each characteristic, comparisons are still necessary to correlate results. In addition, suppliers propose a variety of devices for each test, all of which are of course supposed to provide perfect compliance with the test standard. However, certain devices have been in use for over than ten years, long before the last standard was issued. Modifications in test conditions appeared during the final phases of the European test standardization process. Round robin tests are very expensive and time consuming, but they are necessary to compare laboratory findings when different devices are used to perform tests. For indirect tension modulus tests, only a few round robin tests were conducted in the past, and this was well before the final version of the existing standard. This paper presents a comparative test conducted in 6 laboratories of the Colas group with three different devices, from two suppliers. Two different asphalt mixes have been selected, a common asphalt concrete used for wearing courses and a High Modulus Asphalt (HMA) mix. Samples were made, controlled, and characterised in a single laboratory before they were sent to the participants. Results obtained show that devices provide very similar results, if samples are cautiously moulded and controlled. It is also possible, using correlations between results obtained with different modulus tests, to show that we are able to predict modulus in direct tension tests from indirect tension tests.
