Effect of different vinyl-acetate contents in hybrid SBS-EVA modified bitumen

One of the most common polymers for bitumen modification and polymer-modified bitumen is Ethylene-vinyl acetate (EVA). Although of standard use, EVA can assume very different acceptations depending on the VA content within the copolymer matrix; low VA contents make EVA similar to a tough plastic while higher VA content makes it similar to a flexible rubber. The current study was conducted to evaluate the effect of vinyl acetate (VA) content on the performance of polymer-modified bitumen. In this study, base bitumen was modified with both styrene butadiene styrene (SBS) and EVA with 9%, 12%, 18%, and 24% VA content. A reference modified bitumen with SBS and low-density polyethene (LDPE) is also studied. Tensile strength tests were initially conducted on the single and hybrid polymers only, prior to bitumen addition. Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and rheological tests were then carried out on the polymer-modified bitumen. The results from the thermal analysis concluded that the increase in vinyl acetate hinders the crystallization of the polymer, thus reducing the melting temperature and enthalpy. The rheological results showed that modifying bitumen with various EVA has allowed the formation of a rigid three-dimensional network when the polymers are dispersed within the bitumen thus improving the rheological behaviour primarily at low frequencies (high temperature).