A mixture-based Black Space parameter for low-temperature performance of hot mix asphalt

Low-temperature cracking is a critical distress form and is heavily influenced by the relaxation and strength capabilities of the material. These properties are related to the stiffness through principles of viscoelasticity. Recently, there is elevated pressure on decisions made by pavement and materials engineers to produce the longest lasting, most resourceful pavement systems possible to optimise monetary and non-renewable resource usage. The primary objectives of this study are to: (1) assess the value of a parameter which can describe low-temperature cracking resistance by using dynamic modulus (|E*|) and phase angle (δ) of the mixture and laboratory-measured performance; (2) present shape parameters of a mixture master curve that are directly related to the relaxation spectra, which is expected to play a pivotal role in low-temperature distress resistance with ageing; (3) define failure lines in Black Space which correspond with laboratory-measured performance and operate under a well-understood basis reinforced by the literature; and (4) provide agencies with a tool to aid in the movement towards a performance-based mixture design, acceptance, or rehabilitation decision-making system. An analysis of the mixture master curve is done to establish parameters which describe the relaxation spectra and ageing potential of materials. A mixture-based Black Space parameter is presented based on results from the |E*| master curve construction and the thermal stress restrained specimen test. This approach holds promise, but must be calibrated with a robust database before serious implementation considerations are made. Future work will look to determine a common stiffness condition to better define the failure threshold and to identify possible alternatives to the modified Glover–Rowe function used in this study. Further evaluation is also needed to optimise the temperature–frequency combination of the Black Space parameter itself and ensure a condition is specified that can be captured by test equipment an owner agency or contractor may possess as part of a performance-based specification framework.