Prediction of permanent deformation of asphalt concree in cyclic and monotonic loading: Fid-Bau Portal

Prediction of permanent deformation of asphalt concree in cyclic and monotonic loading

Ramsamooj, D.V. / Ramadan, J.

New theoretical developments are presented to predict the permanent deformation in asphalt concrete caused by constant-load creep and by cyclic loads. The constitutive model utilizes multi-yield surfaces and isotropic hardening. A new hardening law for the changes in the values of the plastic moduli during monotonic or cyclic loading is derived from Rowe's stress-dilatancy theory. A complete description of the permanent deformation of asphalt concrete under constant load creep and cyclic loading is given, including the elastic, viscoelastic, plastic, and microcracking components, to predict the permanent deformation under cyclic loading. The model parameters have clearly defined physical meanings and can be determined from simple conventional laboratory tests. A computer program called RUT determines the permanent deformation. There is good agreement between the model predictions and the experimental data. The model predictions agree reasonably well with the experimental data for creep and cyclic loading. This means that the rutting from the plasticity of the asphalt concrete follows Rowe's stress-dilatancy theory and the new hardening law. The behavior of the asphalt concrete during cyclic loading is consistent with linear viscoelasticity at the lower stress levels, but is dominated by plasticity and microcracking at the higher stress levels. For creep under constant loading, there is an initiation time for cracking to commence that is dependent on, and increases rapidly with, the stress level. Creep at advanced stages follows Cherepanov's theory for the rate of crack propagation. The results indicate that rutting can be decreased by selection of a dense-graded aggregate with a high value of K, the coefficient of lateral pressure. Asphalt concrete made with polymer-modified asphalt cement (SBS) has a high value of K compared with that of AC 10 and AC 20, so that the former exhibits a higher resistance to rutting. The model shows that microcracking and its contribution to rutting can be minimized by using a DGAC with high tensile strength and fracture toughness. The computer program RUT (available on request) is user-friendly. The input is simple and the output gives all of the information needed for practical purposes. The parameters needed to predict the rutting of any asphalt concrete are the tensile strength, the fracture toughness, and the hardening rate, together with the viscoelastic stress/strain curve at a very low stress and stress/strain curve to failure. All parameters have well-defined physical meaning and can be determined easily by conventional tests.