Characterisation of high modulus asphalt (EME) mixes, focussing on flexural response and fatigue

[摘要] ENGLISH ABSTRACT: The road construction industry is faced with the challenge of designing and constructing high performance asphalt materials to meet the ever growing demand of increasing traffic volumes and axle loadings. EME (Enrobés à Module Elevé) or simply high modulus asphalt was developed in France in the mid-seventies. EME asphalt provides a high performance material for the use in heavy duty pavements. EME asphalt has a very high resistance in terms of permanent deformation as well as a stiffness surpassing that of standard mixes used in base layers. EME mixes also have a good resistance to fatigue due to the high binder content of the mix.Numerous studies have investigated the fatigue resistance of hot-mix asphalt (HMA) mixtures, with limited research into EME mixes on the basis of its material properties and structural responses. In this study, a Four Point Beam fatigue apparatus was used to measure the fatigue response of a certain EME mix at various strain values (50, 100, 175, 250 με) and temperatures (10 and 40˚C) under a pulse frequency of 10Hz. Both a haversine and sinusoidal loading profile was investigated in terms of the Four Point Beam Test (4PBT). In this regard, it was concluded that sinusoidal loading was the only viable loading option. At low temperatures and high strain values, haversine loading caused premature failure in a number of beam specimens. This conclusion was confirmed with the help of a numerical analysis, done in ABAQUS FAE, in order to investigate initial tensile stresses in the beam specimens with the application of both loading profiles.Witczak, et al. (2013) indicated that during the sinusoidal test, the deflection pattern is sinusoidal, bending the beam specimen in both directions. The neutral axis of the beam stays unchanged during the test, as it remains in the original position halfway between the two extreme deflection positions. During the haversine test, the deflection pattern is haversine, bending the beam with the same peak-to-peak magnitude as the sinusoidal test but only in one direction. Because of the static force component in the load signal and the viscous character of the material, creep (permanent deformation) will occur in the beam, causing the neutral axis of the beam to shift downwards after a few loading cycles. After the shift of the neutral axis the original haversine loading pattern will become a sinusoidal loading pattern with respect to the new neutral axis. This phenomenon was confirmed through the applied loading outputs from the 4PBT.Using the Four Point Beam apparatus, frequency-temperature sweeps were done at pulse frequencies of 0.5, 1, 2, 5 and 10 Hz with conditioning temperatures ranging from 10˚C to 40˚C at 5˚C intervals. The frequency and temperature sweeps were done to develop the stiffness Master Curves, in order to create a framework for predicting stiffness versus loading time relationship for the investigated EME asphaltic material.In this study, principles regarding EME, findings on the flexural fatigue performance and discussions of data as well as recommendations and conclusions are made. The recommendations serves as a vital part of the research study as EME testing, in South Africa, has not yet been conducted on the scale in which it is covered during this study. The recommendations would thus be helpful with regards to future testing and research on the subject.

[发布机构] Stellenbosch University