Optimization of Bonding Behavior of Crumb Rubber-Modified (CRM) Asphalt for Sustainable High-Friction Surface Treatment (HFST) Applications

Binder bonding strength (BBS) is critical to aggregate retention and friction performance in high-friction surface treatment (HFST). Although epoxy resin is traditionally used, asphalt-based binders offer a sustainable alternative; however, their bonding behavior and influence on polishing performance remain insufficiently understood. This study investigated the evolution and optimization of BBS in crumb rubber-modified (CRM) asphalt for rhyolite-based HFSTs. BBS was measured under dry and wet-conditioned states for two CR contents (10% and 15%), two CR types (cryogenic and ambient), two interaction temperatures (170 and 200 °C), and interaction times from 10 to 240 min. HFST performance was assessed using the British pendulum tester (BPT), dynamic friction tester (DFT), and circular track meter (CTM) under accelerated polishing. CR modification reduced dry BBS relative to the base binder but substantially improved moisture resistance: wet conditioning reduced base-binder BBS by 23.8%, versus 5.8–9.8% for CRM binders. BBS evolution was temperature-dependent. At 170 °C, BBS decreased and gradually recovered through 240 min, while binders prepared at 200 °C peaked at 120 min before declining. Type III factorial ANOVA identified CR content as the dominant factor affecting BBS, with interaction temperature, interaction time, and their combined effects also being significant. Despite lower BBS, 15% CRM binders generally retained higher HFST friction performance than 10% binders after accelerated polishing. The moderate relationship between dry BBS and coefficient of friction (COF) loss (R2 = 0.68) confirmed that BBS alone could not predict HFST durability, while a stronger BPN-COF loss correlation (R2 = 0.79) confirmed consistent rankings across friction test methods. Cryogenic CRM prepared at 200 °C for 120 min provided the best balance among bonding development, rheology, and friction retention. These findings demonstrate that while bonding strength alone does not govern HFST durability across interactions, its evolution with interaction time exerts a significant effect on friction retention within a given interaction condition, highlighting interaction-time optimization as a critical parameter for developing sustainable CRM-based HFSTs.