Modulus measurement: European standardisation possibilities

The recent publication of EN standards has yielded five different recognized tests in EN 12697-26, which means that each of these tests only has small-scale experience and practice in a limited number of countries. Test conditions are specified in asphalt mix design EN 13108-20. There are significant differences in these test conditions, frequency between 8 and 10 Hz for cyclic loading, pulse loading of 124 ms or extrapolation to 0,02 s for loading time in direct tension, and a temperature test of 15 or 20 degrees C. The cost of the equipment and the needed experience obviously means that only one test will be selected because it is difficult and unnecessary to purchase all the devices and to have skilled technicians able to conduct the entire range of tests. Nevertheless it is interesting for mix design specialists to be able to correlate results from different tests. It is important to be able to estimate which level of performances corresponds to a mix design that has already been evaluated with another test and to check coherence regarding fundamental requirements. This last point is even more important because the possibilities given in EN standards lead to significant differences in measured characteristics, with results that may vary for example between 6,000 and 10,000 MPa for the same mix. We present here modulus results obtained with 4 mechanical tests on two asphalt mixes, a BBSG (semi-coarse asphalt mix) and an EME (high modulus asphalt mix). We show also first results regarding correlation between four-point bending and direct tension tests. These data complete works previously published by the Colas Group on the diffusion of the law of simple correlations between the results of modulus tests. These two mixes are also characterised with the Simple Performance Test. This is a first comparison between results with the SPT and tests used in Europe.