Polyolefin–Based Bitumen Modifiers for Durable Asphalt Pavements: Structure–Property Relationships, Compatibilization Strategies, and Design Implications

Polyolefin-based bitumen modifiers are emerging as cost-effective, circular alternatives to styrene-based elastomers in road construction. Their tunable mechanical performance and saturated backbone suit diverse climates, however, the chemical inertness and poor affinity to asphaltenes often compromise binder compatibility and storage stability. This review describes recent advances in polyolefin-modified bitumen from polymer- and bitumen-science perspectives, emphasizing how modifier architecture, functionalization route, and binder hybridization strategies influence phase structure and rheological response. The physicochemical nature of bitumen-polyolefin interactions is first addressed to elucidate underlying incompatibility mechanisms. The discussion provides insight into metallocene-catalyzed polyolefin elastomers, vulcanizable polyolefin rubbers, and functionalized polyolefins prepared via reactive extrusion, high-pressure polymerization, or catalytic functionalization. Further, more complex hybrid systems combining crumb rubber from post-consumer tires and polyolefin-based compatibilizers are critically reviewed. For each presented modifier class, microstructure, storage stability, and linear/nonlinear rheological assessments are evaluated to identify structure–property correlations and effective bitumen modification and compatibilization strategies. This work synthesizes literature reports into a unified framework that systematically catalogues recognized compatibilization approaches for enhancing the miscibility and performance of polyolefin–based binders. It concludes with design implications and research priorities for translating these insights into high–performance, sustainable paving materials approaching the performance targets set by styrene–based elastomer technologies.