Development of a phenomenological constitutive model for fracture resistance degradation of asphalt concrete with damage growth due to repeated loading


Discontinuous areas under the asphalt concrete (AC) layer, such as joints and cracks in an underlying layer, induce higher stress concentration than the designed strength. Stress concentration in the vicinity of discontinuities accelerates distress on the AC layer. Repeated traffic and environmental loading applied to the AC layer also induce degradation of the layer’s strength as microcracks grow at stress levels lower than the layer’s designed strength. In addition, this could be magnified when combined with low temperature cracking, one of the main distresses in AC pavements resulting from extreme temperature changes. When loading is applied near the joints or discontinuity, it amplifies the tensile stress at the bottom of the AC layer as well as the shear stress when the Portland cement concrete (PCC) slab or discontinuity moves vertically. Repetitive traffic loading and environmental changes cause continuous damage accumulations which consequently results in the acceleration of movement in the AC layer at the localized area close to the discontinuity region, thus leading to mechanical degradation of the AC materials which become less resistant to fracture. Even a small load can result in fracture failure of AC pavements when the loss of strength in AC pavements progresses significantly through repeated loading. The current approach to determine the critical properties of AC materials is to conduct laboratory testing under monotonic loading and cyclic loading separately. The fatigue testing under cyclic loading can only provide bulk material properties without consideration to any discontinuities, such as cracks in underlying pavement or joints. On the other hand, the current fracture tests conducted under monotonic loading fail to capture the loss of material strength as repeated loading is applied on pavements. For an accurate estimation of pavement life, it is essential to consider the effect of repeated traffic and thermal loading on the fracture resistance of the AC materials. This study investigates the degradation of the fracture resistance of AC materials as a result of the progressive damages caused by repeated loading application. The study develops the phenomenological constitutive model for fracture resistance degradation with damage growth caused by repeated loading. An experimental program was designed to apply monotonic and cyclic loading to the same test geometry and to examine the degradation of fracture properties with damage growth at the crack tip. Fracture and fatigue tests were implemented using semi-circular bending (SCB) test geometry with notched specimens at various temperatures, loading frequencies, and loading amplitudes. It is observed that damage functions and proposed parameters reflect the degradation rate of fracture resistance with respect to damage growth at the notch tip region. A presented constitutive model accurately predicts the remaining service life of existing pavements. It is further observed that the model coefficient distinguishes AC materials in terms of sensitivity to cracking resistance under both monotonic and cyclic loading.U of I OnlyGraduate College 2-year Extension For

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