Nano-TiO2 in Asphalt Pavements: A Critical Review of Phase-Dependent Reinforcement and Environmental Viability

• Rutile phase is proposed as a theoretical micro-anchor for pavement reinforcement. • Nano-TiO2 raises binder viscosity by 109% and reduces rut depth by 34%. • Enhanced pavement durability amortizes the initial carbon deficit of nano-TiO2. • Cold-applied photocatalytic systems reduce total energy use by over 80%. • The Central European framework addresses harsh winter maintenance and abrasive wear. While nano-titanium dioxide (TiO₂) is widely recognized as a functional additive for air-purifying infrastructure, current research frequently overlooks its impact on the asphalt matrix's structural integrity. This multi-scale review bridges chemical photocatalysis and pavement engineering through five objectives: (i) synthesizing photocatalytic advancements, (ii) evaluating field durability factors, (iii) analysing TiO₂ as a structural reinforcing agent, (iv) examining life-cycle sustainability and health risks, and (v) exploring innovative transparent-binder systems. Analysing literature (1997–2025) reveals a systemic disconnect: while anatase is the empirically proven standard for NOx degradation, this review proposes rutile as a theoretical micro-anchor for structural reinforcement due to its higher density and hardness. Aggregated data indicate TiO₂ provides physical and physicochemical reinforcement—restricting asphaltene mobility at the molecular level—which increases binder rotational viscosity by up to 109%, reduces rut depth by 34%, and elevates the Performance Grade (PG). Furthermore, an LCA paradox demonstrates that although TiO₂ functionalization increases material production emissions by 17.07%, this initial carbon deficit is effectively amortized through enhanced mechanical durability and life-cycle extension. Additionally, cold-application technologies (e.g., micro-surfacing) can reduce total energy consumption by over 80% compared to hot-mix asphalt. The study concludes by proposing a Central European framework advocating for theoretical rutile-reinforced porous systems and hybrid-phase blending to withstand harsh winter maintenance while maintaining photocatalytic efficacy.