Semi-flexible pavement: a review of material mechanisms, performance controversies, design methods, and functional frontiers

Semi-flexible pavement (SFP) is a multi-phase composite produced by filling interconnected voids of a porous asphalt mixture (PAM) skeleton with high-fluidity cementitious grouting material (GM). While this interpenetrating structure delivers exceptional rutting resistance and structural capacity for heavy-duty applications, it introduces persistent challenges regarding asphalt–cement interfacial bonding, phase compatibility, and long-term durability. This paper provides a comprehensive synthesis of SFP technology from microstructural mechanisms to functional applications. First, mechanical behavior is deconstructed by examining synergistic load-transfer among PAM skeleton, hardened GM network, and critical interfacial transition zone (ITZ). Second, fatigue and low-temperature cracking controversies are organized in a unified damage-evolution framework linking loading/thermal restraint, local GM cracking and ITZ debonding, stiffness redistribution, energy dissipation, and final crack localization, explaining why stress- vs. strain-controlled tests and stiffness- vs. energy-based criteria yield different evaluations. Third, an integrated design methodology links PAM void connectivity, GM optimization, quantitative grouting saturation control, and non-destructive quality assurance and quality control techniques. Finally, emerging functional and sustainable applications are assessed with emphasis on whether environmental benefits can be achieved without compromising mechanical durability or service life. This review establishes a roadmap for performance-based design, advanced quality control, and life-cycle evaluation of next-generation SFP infrastructure.