Multi-scale optimization of epoxy content in asphalt binders: enhancing mechanical, microstructural, and molecular properties

The main application scenarios of thermosetting epoxy asphalt binder are currently restricted to steel bridge deck pavement and airport pavement. Up to 50% of the epoxy system (ES) content limits its wider application because of its high cost. To explore a more economical ES range, 20%, 30% and 40% ES were added to virgin asphalt-epoxy system, aged asphalt-epoxy system and aged asphalt + rejuvenator-epoxy system. The effects of ES content on the mechanical properties, microstructure and molecular behaviour were investigated by macroscopic and microscopic experiments. Results show that the curing reaction is the fastest in the first 40 min for all systems, regardless of ES content. The addition of rejuvenator can reduce the viscosity of aged asphalt-epoxy system and improve tensile and low-temperature properties. With the decrease of ES content, the cross-linked network gradually loosens until it disappears. Aged asphalt is more conducive to ES curing and cross-linked structure formation than virgin asphalt. For aged asphalt + rejuvenator-epoxy system, the optimal ES content is 30%, which enables it to have good macro- and micro-properties while reducing material costs.