<title>Laser removal of surface and embedded contaminations on/in building structures</title>

Abstract

This paper demonstrates the technical feasibility and basic phenomena of using laser techniques for the non-contact removal of embedded contamination down to depths of 0.1 - 4 mm thick in construction materials such a concrete, brick, plaster/mortar, stones and stainless/mild steels. In this study a high power CO<SUB>2</SUB> laser and a YAG laser were used. The techniques investigated include laser vaporization removal, laser combustion/decomposition removal, laser melt ejection removal, laser thermal fracture removal and laser HAZ delamination removal. The work showed that melt ejection removal can be applied to metal objects with removal depth up to 1.5 mm/pulse while the other four methods are more effective for nonmetallic materials with removal depth up to 3 mm for each pass. Particularly when hydraulic bond materials such as concrete, cement, mortar/plaster, rendering and stones are involved the thermal fracture and HAZ delamination methods were found very effective. Paint, epoxy, and plants such as moss and lichen on the construction bodies can be removed effectively by laser generated combustion/combustion. One of the advantages of laser contamination removal is the energy controllability, remote operation capability (convenient for nuclear decontamination), low waste and high efficiency. In addition amorphous glazing can be generated on the surfaces of construction materials such as bricks and concrete during vaporization removal providing a means of sealing the remaining surface. Optical microscopy, SEM, EDAX, and x-ray diffraction were used to study the affects of laser treatment under various conditions. Mathematical representation of the processes were discussed. Comparison was made between the methods and optimum operating condition provided.