EFFECT OF AGEING ON ROAD BITUMEN MODIFIED WITH THE ETHYLENE VINYL ACETATE POLYMER
Last modified: 2017-02-28
The increase in axle loads, heavy traffic, severe climate conditions and construction failures has led to the enhancement of bitumen properties. There is a wide range of applications of polymer modified bitumens, PmBs, in road construction. Polymer modification significantly influences the rheological characteristics of the binder; therefore the use of fundamental rheological testing methods is required rather than the empirical methods. This paper presents the polymer modification of road bitumen, BIT, with different contents of semi-crystalline thermoplastic copolymer ethylene- vinyl acetate, EVA, before and after thermo-oxidative ageing. The effects of EVA on the conventional, rheological and thermal properties of the modified bitumens were studied. The rheological characteristics of the EVA PmBs were analyzed by a dynamic shear rheometer, DSR. The primary viscoelastic functions were determined in dependence as a function of the frequency at temperatures in BIT use. The master curves were designed at a reference temperature of 30°C.The results indicated that the thermoplastic copolymer EVA improves the viscoelastic properties of PmBs. EVA PmBs increase stiffness and elasticity at high service temperatures and low loading frequencies. The increased stiffness compared to the conventional bitumen enhances the performance characteristics of the modified bitumen and provides better protection against increased traffic loads and adverse climate conditions. The process of ageing increased the complex modulus and phase angle, and reduced temperature susceptibility. These changes were mainly due to the chemical processes, such as degradation reactions, oxidation as well as secondary processes of cross-linking which take place during the ageing of BIT and EVA PmBs. PmBs modified with EVA significantly reduce the permanent deformation under loads compared to the unmodified bitumen.
polymer modified bitumen; rheological properties; thermal properties; thermooxidative ageing; permanent deformation