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This paper presents the results of a review on variability of key pavement design input variables (asphalt modulus and thickness, subgrade modulus) and assesses effects on pavement performance (fatigue and deformation life). Variability is described by statistical terms such as mean and standard deviation and by its probability density distribution.
The subject of reliability in pavement design has pushed many highway organisations around the world to review their design methodologies, mainly empirical, to move towards mechanistic-empirical analysis and design which provide the tools for the designer to evaluate the effect of variations in materials on pavement performance. This research has reinforced this need for understanding how the variability of design parameters affects the pavement performance.
This study has only considered flexible pavements. The sites considered for the analysis, all in the UK (including Northern Ireland), were mainly motorways or major trunk roads. Pavement survey data analysed were for Lane 1, the most heavily trafficked lane. Sections 1km long were considered wherever possible.
Statistical characterisation of the variation of layer thickness, asphalt stiffness and subgrade stiffness is addressed. A sensitivity analysis is then carried out to assess which parameter(s) have the greater influence on the pavement life.
The research shows that, combining the effect of all the parameters considered, the maximum range of 15th and 85th percentiles (as percentages of the mean) was found to be 64% to 558% for the fatigue life and 94% to 808% for the deformation life.
The Vialit Cohesion Pendulum has been used for many years in Europe as a tool for assessing modified asphalt binders with a particular emphasis on chip seal/surfacing dressing applications. The cohesion measured in this device has been considered as an indicator of quality of the base asphalt binder and subsequent polymer formulation. This test demonstrates a transition between brittle and ductile failure of binder systems. When a test of this kind is compared to other binder tests, it is possible to deduce the impact that the high rate of loading in the Vialit Cohesion Pendulum test has on the test results. Data have been developed on a series of SHRP core asphalt binders and these are compared to master curves developed with the same binders. A discussion will follow on how the fracture of asphalt binder and mixture is both rate and temperature dependent and that this parameter always needs that consideration to truly evaluate the meaning of test data. A test of this nature, while founded partly on an empirical data base of use, can be better explained and understood with consideration of the speed of loading and temperature effects that allows the translation of fracture temperatures at one condition to those at another. The results from this type of evaluation offer better understanding of criteria such as fatigue, fracture and bond of asphalt binders and mixtures.