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 ft and “structural” fracture toughness KIC have been determined by this composite model from experimental results of notched beam specimens of any size with any notch length. Temperature (T) dependent ft and KIC measurements of asphalt concrete from −10 to + 23 °C, relevant to the real temperature environments, are then determined. The characteristic microstructure Cch in the model is the average aggregate size. The maximum failure load Pmax of asphalt concrete under three-point-bending (3-p-b) is linked directly to its constant “structural” tensile strength ft for a given temperature environment, independent of sample size and notch/crack length. In addition, although KIC is not valid for asphalt pavement with limited thickness, its influence is reflected through the “structural strength” criterion based on ft and Cch. This simple model can also be used as a design tool for asphalt concrete property optimization.