Laser scabbling of cementitious materials

• Main Author: Peach, Benjamin
• Other Authors: Petkovski, M. ; Engelberg, D. L. ; Blackburn, J.
• Published: University of Sheffield 2015
• Subjects: 624
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678771

Laser scabbling of concrete is the process by which the surface layer of concrete may be removed through the use of a high power (low power density) laser beam. The aim of this study was to investigate the mechanism(s) responsible for laser scabbling. This was achieved in three stages. The first stage was a test series used to establish an experimental procedure for assessing the effects of various parameters that may be critical for the effectiveness of the process, such as material composition and initial moisture content. The second stage was a test series investigating the effect of concrete composition on laser scabbling. The first two test series identified that the driving force of laser scabbling in concretes originates from the mortar, therefore, the third test series concentrated on the factors that influence laser scabbling of mortars. Throughout the study, infra red recordings have been used to quantify laser scabbling behaviour, along with the volume removal due to laser scabbling and characterisation techniques such as XRF, DTA and TGA. The results suggest that scabbling is mainly driven by pore pressures, but strongly affected by other factors. The removal of free water from mortars prohibits scabbling, but resaturation allows mortar to scabble. A reduced permeability, either due to a reduction in the water/binder ratio or the use of 25% PFA replacement, enhances laser scabbling. Results show that the biggest effect of ageing is due to specimens drying. Mortars and cement pastes were seen to scabble at a constant rate, whereas concretes experienced a peak rate, after which volume removal reduced dramatically. Basalt aggregate concrete was less susceptible to laser scabbling than limestone aggregate concrete due to vitrification. A higher fine aggregate content increases volume removal and fragment sizes during laser scabbling.