Relaxation spectra of asphalt binders and the Christensen-Anderson rheological model

The development of the well-known Christensen-Anderson (CA) rheological model grew out of attempts to model the relaxation spectra of asphalt binders using a skewed logistic distribution function. For this reason, there exist very strong relationships between the CA model parameters and the characteristics of relaxation spectra for asphalt binders. This paper presents a recently developed equation that allows direct and accurate calculation of the relaxation spectra from CA model parameters, demonstrating the nature of this relationship. Of the CA model/spectrum parameters, the most important in terms of describing overall behaviour and potential performance is the R-value, which describes the shape and skewness of the spectrum. This parameter and other similar rheological parameters have been linked to various important aspects of asphalt binder behaviour, including fatigue resistance, chemical composition and degree of oxidative ageing. This makes the parameter R a potentially useful parameter for inclusion in asphalt binder specifications, although care must be taken in how it is determined to ensure that it is accurate, repeatable and reflects the performance characteristics of interest.