Multi-scale investigation into the formation mechanism of efflorescence on concrete bridge deck pavements: from macro construction quality to micro material characterization

Efflorescence severely impairs concrete bridge deck pavement durability and aesthetics, yet its formation mechanisms regarding construction and environmental drivers remain unclear. This multi-scale study investigates efflorescence origin and migration via field surveys, structural detection, environmental monitoring, and micro-characterization. Field investigations classified efflorescence into five patterns concentrated in traffic lanes. Structural analysis revealed that construction defects—specifically milling depth variations (up to 1.96 cm) and localized depressions (~20 mm)—create ‘catchment zones’ hindering drainage. Environmental monitoring demonstrated that atmospheric pressure differentials (up to 0.8 kPa) and diurnal temperature variations (15 °C) drive moisture migration. Furthermore, XRD and SEM-EDS confirmed the efflorescence is a chemical precipitate overwhelmingly dominated by calcite (CaCO3) derived from the carbonated cement matrix (19.6 wt% Ca). The complete absence of unhydrated clinker or basaltic tracers explicitly excludes the physical migration of raw materials. Results indicate efflorescence follows a ‘Leaching–Migration–Carbonation’ mechanism: water retained in depressions dissolves alkaline components, migrates upward under environmental pumping, and crystallizes upon carbonation. These findings highlight the critical need to improve milling precision and drainage design to mitigate moisture-induced distress.