A unified method for the analysis of nonlinear viscoelasticity and fatigue cracking of asphalt mixtures using the dynamic mechanical analyzer

摘要

Fatigue cracking is one of the primary modes of distress in asphalt pavements that has animportant economic impact. Fatigue resistance characterization of an asphalt mixture is acomplex issue due to: (i) composite nature of the material, (ii) gradation of aggregateparticles, (iii) variation of asphalt film thickness, (iv) air voids distributions, (v) asphaltbinder nonlinear viscoelastic behavior, (vi) effects of binder oxidative aging as afunction of time, and (vii) micro crack healing during rest periods. Different methods toassess fatigue cracking in asphalt materials are available in the literature. However, thereis no methodology to characterize fatigue cracking behavior of asphalt materials that isindependent of the mode of loading (controlled-strain or controlled-stress). The objectiveof this research is to develop a new methodology to characterize fatigue cracking of thefine aggregate matrix (FAM) portion of asphalt mixtures using dynamic mechanicalanalyses (DMA). This is accomplished through different, but related, approaches. Thefirst approach relies on identifying the various mechanisms of energy dissipation duringfatigue cracking that are manifested in: (i) nonlinear viscoelastic deformation, (ii)fracture, and (iii) permanent deformation. Energy indices were derived to quantify eachof these energy dissipation mechanisms and to quantify fatigue cracking irrespective ofthe mode of loading. The first outcome of the approach is a fatigue damage parameter(crack growth index) that provides comparable results for a given material even whentested under different modes of loading and different load (strain or stress) amplitudes. The developed fatigue characterization method has a lower coefficient of variation whencompared to conventional parameters (number of load cycles to failure or cumulativedissipated energy). The crack growth index parameter was also qualitatively andquantitatively compared to three dissipated energy methods available in the literature.The second outcome of this research is a constitutive model that can describe bothasphalt mixtures? nonlinear viscoelastic response and fatigue damage in one formulation.Nonlinear viscoelastic as well as damage parameters were obtained for both modes ofloading. This second approach has the advantage that the constitutive model can beimplemented in a numerical framework to describe the response of asphalt mixturesunder various boundary conditions.