Modelling and testing of Temperature-Dependent strength and toughness of asphalt concrete from −10 °C to + 23 °C using small notched beams

A closed-form fracture model with the consideration of the average aggregate size and crack-tip damage zone is used to analyse flexural strength of asphalt concrete using notched beams. Quasi-stable micro-crack formation and quasi-brittle fracture of these small samples with highly heterogeneous aggregate structures are formulated. While the apparent strength and fracture toughness of asphalt concrete based on Continuum Mechanics are size dependent, constant asymptotic “structural” tensile strength f_t and “structural” fracture toughness K_IC have been determined by this composite model from experimental results of notched beam specimens of any size with any notch length. Temperature (T) dependent f_t and K_IC measurements of asphalt concrete from −10 to + 23 °C, relevant to the real temperature environments, are then determined. The characteristic microstructure C_ch in the model is the average aggregate size. The maximum failure load P_max of asphalt concrete under three-point-bending (3-p-b) is linked directly to its constant “structural” tensile strength f_t for a given temperature environment, independent of sample size and notch/crack length. In addition, although K_IC is not valid for asphalt pavement with limited thickness, its influence is reflected through the “structural strength” criterion based on f_t and C_ch. This simple model can also be used as a design tool for asphalt concrete property optimization.