Linear and non-linear viscoelastic behaviour of selected neat and polymer modified asphalts (PMAs)

Asphalt binder plays a major role in determining the performance of the asphalt concrete pavements. Asphalt industry has realized that ever increasing demand in terms of performance of asphalt concrete pavements can not be met with conventional asphalt binders. This has led to the development of improved asphalt binders using various modifiers. Polymer modification has been recognized as one of the most effective methods of improving the performance of binders. Understanding the behaviour of these new materials is of utmost importance due to the wide range of loadings and environmental conditions that these binders will confront once used in the asphalt concrete pavements.; This research work studies the binder behaviour in the linear as well as in the non-linear domains. Linear viscoelastic study was done using dynamic mechanical analysis. Time temperature superposition was used in creating the master curves of polymer modified and unmodified asphalts. It was noted that polymer modified asphalts undergo a wider relaxation process compared to conventional asphalt. Temperature susceptibility of unmodified asphalts was compared to modified binders and it was seen that at mid temperatures polymer modified binders show significantly less susceptibility to temperature variations. Suitability of Ethylene-Vinyl-Acetate and Styrene-Butadiene-Styrene polymer modified asphalts at lower and higher end of service temperatures respectively was validated.; Binder behaviour in the non-linear domain was investigated with several dynamic and transient shear tests, namely; startup of steady shear, cessation of steady shear, exponential shear growth, interrupted shear and relaxation after a step strain. A non-linear constitutive equation was utilized in modeling asphalt binder responses under above mentioned theological tests. The non-linear effects of these polymer modified asphalts due to large shear strains and strain rates were demonstrated. Interestingly enough, in the case of unmodified asphalt these non-linear responses were either minimum or not seen at all. Existence of a three dimensional physical network structure in polymer modified asphalts was validated and it was shown that this structure can be broken by shearing and given enough rest time the structure re-forms indicating suitability of this type of materials in reducing fatigue and accumulation of permanent deformation.