Inelasticity of Asphalt Concrete under Repeated Compression

ABSTRACT The paper presents the two ‘facets’ of asphalt concrete. Under monotonically increasing uniaxial compression, it demonstrates the elastic features and stress strain pattern typical of ordinary low-strength cement concrete. But under repeated low-rate load, due to fast relaxation, a large part of its deformations is inelastic and irreversible. The model of the stress-strain relationship for monotonic loading comprises the Semi-Gaussian of decreasing integrity, which reflects the nonlinear degradation of asphalt concrete without reference to plasticity. The intrinsic modulus of elasticity decreases only slowly alongside the internal degradation, being independent of the process of relaxation. The stress-strain curve revealed under increased monotonic load is found to be the envelope of the stretch limit, i.e. of the fatigue of the asphalt concrete under compression. An analytical model is presented for predicting this stretch limit and the number of loadings for a given repeated stress with a known duration of cycles. Daily fluctuations of the temperature in restrained asphalt concrete induce low strains and stresses in it, slowly. Fast relaxation transforms them into irreversible deformations which, accumulating, exhaust the stretchability and strength of asphalt concrete and intensify its embrittlement, usually associated with oxidation (aging).