Indirect Tensile Test for the Determination of the Stiffness and the Resilient Modulus of Asphalt Concretes: Experimental Analysis of the EN 12697 -26 and the ASTM D 4123 Standards

The results are presented of a laboratory study on the Stiffness and the Resilient Modulus of bituminous mixes determined by the Indirect Tensile Test, conducted according to the EN 12697-26, Annex C and the ASTM D 4123 standards. The testing was performed on high-performance bituminous mixtures, including polymer modified base-binder and wearing course asphalt concretes, stone mastic asphalt and porous asphalt. The course aggregate grading of all the mixtures contains Electric Arc Furnace (EAF) steel slags, up to a maximum content of 45%. The purpose was first of all to analyze quantitatively the controlled strain and the controlled stress loading procedure, that characterize the EN and the ASTM standards respectively, at various temperatures, strain levels, repetition periods and rise times. A second aim was to check the applicability of the above-mentioned regulations to both dense, as well as porous asphalt mixtures. The results of this study demonstrate that the standard controlled strain loading procedure could have limited applicability, dependant on the mix and testing temperatures. The controlled stress loading procedure is necessary to evaluate the asphalt concretes response at extremely low testing temperatures and high loading frequencies. Finally, the Stiffness and the Resilient Modulus give similar results in most cases.