Enhancing triaxial cyclic compression testing of hot mix asphalt by introducing cyclic confining pressure

Permanent deformation in terms of rutting is a major deterioration mode of bituminous bound pavements. The triaxial cyclic compression test (TCCT) is a scientifically accepted and standardised test method to assess the resistance to permanent deformation. Presently, the standard TCCT according to EN 12697-25 is carried out with cyclic axial loading and constant confining pressure. In road pavements, dynamic traffic loading due to passing tyres leads to cyclic confining pressures. Thus, to bring the TCCT closer to reality, within the study presented in this paper, (a) the radial reaction and its phase lag to axial loading in standard TCCTs is measured and (b) an enhanced TCCT with cyclic confining pressure which takes into account the viscoelastic material response in terms of radial phase lag to axial loading is introduced. In a subsequent test programme, TCCTs with various confining pressure amplitudes are run on different materials and results from standard and enhanced TCCTs are analysed and compared in terms of resistance to permanent deformation. It is shown that the resistance to permanent deformation increases significantly when the viscoelastic material response is taken into account in the TCCTs with cyclic confining pressure.