Standartization requirements for the Swiss annex to EN for complex modulus and resistance to fatigue

The European standards (EN) specify various test methods for the determination of stiffness (complex modulus) and fatigue resistance of asphalt mixtures. Up to date only the two point bending test method (2PB-TR) has been used to determine these properties to satisfy type testing requirements in Switzerland. The Swiss standards have introduced requirements for only two high modulus mixtures AC EME 22 C1 and AC EME 22 C2.

The project was recommended by a previous project (No 1434), with the goal to formulate requirements for additional mixture types. However, the accompanying commission (Begleitkommission) was of the opinion that it was not the job of this research project to produce an update to the Swiss annex but the relevant standardization committee. Therefore this report limits its findings to providing indicative values for different mixture types.

Three types of test methods that are recommended by the European standards for determi-nation of complex modulus (EN 12697-26) and fatigue resistance (EN 12697-24) were used: Four Point Bending with prismatic sample (4PB-PR), Indirect Tensile test on cylindrical sam-ples with pulse load form (IT-CY) and cyclic load form (CIT-CY). Having a variety of test methods allows the industry more flexibility in fulfilling the standard requirements.

Eight Swiss mixtures, three surface, three binder and two base courses, were analyzed with the three test methods. It was shown that the different test procedures investigated in this research project do not deliver the same results for complex modulus and fatigue. This is on the one hand due to the testing mechanisms and on the other due to the dissimilar type testing parameters. Regarding stiffness, the trend and ranking of the materials for two of the three methods (4PB-PR and CIT-CY) is similar for a majority of tested mixtures. IT-CY stiffness tests did not show sensitivity to the mixture type as much as the other tests that use a sinusoidal continuous force application. Therefore IT-CY is not recommended for modulus tests.

Some practical considerations are that fatigue testing using IT-CY require a much longer testing period and production of 4PB-PR samples in comparison to CIT-CY requires larger number of samples (18 vs 9) and therefore more material. 4PB-PR tests induce bending and therefore are a more realistic indication of fatigue. Furthermore due to the quality of the ob-tained results, with respect to the expected ones for eight mixtures, 4PB-PR is proposed to determine the fatigue resistance as opposed to CIT-CY.

Starting date: January 2015

End date: October 2019

 

 

Additional Information

 

Complex modulus (stiffness) for all mixtures obtained with 4PB-PR, IT-CY and CIT-CY methods

Publication

Standartization requirements for the Swiss annex to EN for complex modulus and resistance to fatigue

Reserach Project VSS 2014/502

Report No 1660