Environmentally friendly photothermal reconstruction of cement/asphalt road: Can road markings also be cleaned in such unexpected ways?

This paper innovatively proposes a new method for safe and environmentally friendly road markings removal, using nanosecond pulsed lasers to clean the standard yellow, white, red, and black cold spray markings of cement concrete road and asphalt concrete roads by dry cleaning and wet (liquid-assisted) cleaning. The optimal cleaning process for road markings was explored by changing the laser's energy density and spot overlap ratio. The markings' dry and wet dynamic stripping behavior and removal mechanism was analyzed by combining morphology characterization, EDS analysis, XRD analysis, infrared spectroscopy, infrared images, and a highspeed camera. In the complete cleaning state, markings is entirely removed without damage to the road. Dry laser cleaning can meet the cleaning needs of cement roads, and wet laser cleaning can meet the cleaning needs of asphalt roads. The dry laser cleaning mechanism for yellow and white markings is evaporation and phase explosion caused by thermal ablation, the dry laser cleaning mechanism for red markings is thermal stress vibration, and the dry laser cleaning mechanism for black markings is mainly evaporation caused by ablation. The wet laser cleaning mechanism of each color marking is that the rapid growth of steam bubbles in the superheated liquid provokes the explosive evaporation of the liquid film layer. Laser cleaning can slightly increase cement/ asphalt concrete road roughness and enhance anti-slip performance.