Engineering advances in polymer-modified bitumen for sustainable road construction: a review

Road infrastructure is under increasing pressure from heavier traffic, wider temperature fluctuations, accelerated aging, and stricter sustainability targets. Conventional bitumen, although widely used as a binder in asphalt pavements, often shows inadequate resistance to rutting at high temperatures, fatigue damage under repeated loading, and thermal cracking at low temperatures. Polymer modification has therefore become one of the most effective strategies for improving binder performance and extending pavement service life. Recent studies show that elastomers, plastomers, recycled polymers, and crumb rubber can substantially enhance the viscoelastic balance, durability, and temperature susceptibility of asphalt binders. At the same time, the field is evolving beyond conventional modification toward multifunctional systems integrating waste-derived materials, nanomaterials, self-healing concepts, and smart sensing technologies. Rather than treating polymer modifiers as isolated material classes, this review establishes a structure-interaction-performance framework linking modifier chemistry and processing with polymer-bitumen interactions, morphology evolution, storage stability, binder rheology, and asphalt-mixture and pavement-level performance. The review therefore considers polymer modification across multiple scales, from binder-level physicochemical and rheological behavior to relevant mixture-level mechanical performance and pavement implications. The framework further integrates emerging sustainable and multifunctional strategies, including waste-derived modifiers, polymer-assisted oxidative upgrading, nanomaterials, self-healing systems, and smart pavement technologies.