High power diode laser surface glazing of concrete

This present work describes the utilization of the relatively novel high power diode laser (HPDL) to generate a surface glaze on the ordinary Portland cement (OPC) surface of concrete. The value of such an investigation would be to facilitate the hitherto impossible task of generating a durable and long-lasting surface seal on the concrete, thereby extending the life and applications base of the concrete. The basic process phenomena are investigated and the laser effects in terms of glaze morphology, composition, and microstructure are presented. Also, the resultant heat effects are analyzed and described, as well as the effects of the shield gases, O₂ and Ar, during laser processing. HPDL glazing of OPC was successfully demonstrated with power densities as low as 750 W cm^-2 and at scanning rates up to 480 mm min^-1. The work showed that the generation of the surface glaze resulted in improved mechanical and chemical properties over the untreated OPC surface of concrete. Both untreated and HPDL glazed OPC were tested for pull-off strength, rupture strength, water absorption, wear resistance, and corrosion resistance. The OPC laser glaze exhibited clear improvements in wear, water sorptivity, and resistance (up to 80% concentration) to nitric acid, sodium hydroxide, and detergent. Life assessment testing revealed that the OPC laser glaze had an increase in actual wear life of 1.3-14.8 times over the untreated OPC surface of concrete, depending upon the corrosive environment.