Evaluation of epoxy modification in bitumen

In epoxy-bitumen systems, temperature contributes to the development of physiochemical and mechanical characteristics during curing (chemical hardening) and at the long-term service (oxidative aging) of pavement structures. Hardening (i.e., chemical or oxidative controlled) is a complex phenomenon in epoxy-modified binders and the in-depth exploration of incorporating epoxy chemistry in bitumen is needed to understand the evolution of the properties of these binders in time. Within this framework, changes in two different diluted epoxy-modified binders after oven-hardening for various time scales were analysed by means of Fourier transform infrared spectroscopy, modulated dynamic scanning calorimetry and dynamic shear rheometry. The chemical, thermal and mechanical properties of hardened binders were compared showing remarkable differences in their response under various conditions. The degree of aging was dependent on the level of epoxy modification in bitumen. It was found that the sulfoxide compounds are the most representative index for assessing the oxidative-controlled hardening of epoxy-modified bitumens. The phase angle gives useful information for assessing the long-term aging of modified binders demonstrating a linear relationship between the phase angle and sulfoxide index changes with respect to oxidative hardening. The improved performance (i.e., higher tensile strength, flexibility and enhanced longevity) of newly modified binders was demonstrated as well. Overall, the enhanced resistance against aging in combination with the superior mechanical characteristics when the epoxy modification is implemented in bitumen promises a very effective technology for developing long-lasting pavement materials.