The wear characteristics of a high power diode laser generated glaze on the ordinary Portland cement surface of concrete

The ordinary Portland cement (OPC) surface layer of concrete, which was glazed using a high power diode laser (HPDL), has been tested in order to determine the wear characteristics of the glaze. The work showed that the generation of a surface glaze resulted in the considerable enhancement of the wear characteristics over an untreated OPC surface of concrete. Within both normal and corrosive (detergent, NaOH and HNO3) environmental conditions the wear rate of the HPDL generated glaze was 3.5 mg.cm-2.h-1. In contrast, the untreated OPC surface of concrete exhibited a wear rate of 9.8 - 114.8 mg.cm-2.h-1 when exposed to the various reagents. Life assessment testing revealed that the laser glazed OPC surfaces effected an increase in actual wear life of 1.3 to 17.7 times over the untreated OPC surface of concrete, depending upon the corrosive environment. The reasons for these marked improvements in the wear resistance and wear life of the HPDL generated glaze over the untreated OPC surface of concrete can be attributed to firstly, the vitrification of the OPC surface after HPDL treatment which subsequently created a much more dense and consolidated surface, and secondly, the generation of a surface with improved microstructure and phase which is more resistant in corrosive environments

A comparative analysis of the wear characteristics of glazes generated on the ordinary Portland cement surface of concrete by means of CO2 and high power diode laser radiation

The wear characteristics of a glaze generated on the ordinary Portland cement (OPC) surface of concrete using a 2 kW high power diode laser (HPDL) and a 3 kW CO2 laser have been determined. Within both normal and corrosive environmental conditions, the wear rate of the CO2 and HPDL generated glazes were consistently higher than the untreated OPC surface of concrete. Life assessment testing revealed that surface glazing of the OPC with both the CO2 and the HPDL effected an increase in wear life of 1.3 to 17.7 times over an untreated OPC surface, depending upon the corrosive environment. The reasons for these marked improvements in the wear resistance and wear life of the CO2 and HPDL generated glazes over the untreated OPC surface of concrete can be attributed to the partial (CO2 laser) and full (HPDL) vitrification of the OPC surface after laser treatment which subsequently created a much more dense and consolidated surface with improved microstructure and phase characteristics which is more resistant in corrosive environments. In addition, the wear life and the wear rate of the HPDL glaze was found to be consistently higher than that of the CO2 laser glaze. This is due to the fact that CO2 and HPDLs have very different wavelengths; consequently, differences exist between the CO2 and HPDL beam absorption characteristics of the OPC. Such differences give rise to different cooling rates, solidification speeds, etc and are, therefore, the cause of the distinct glaze characteristics which furnishing each microstructure with its own unique wear resistance characteristics

The influence of shield gases on the surface condition of laser treated concrete

This work aims to elucidate the effects of using O2, Ar and He shield gasses during the treatment of the ordinary Portland cement (OPC) surface of concrete with a high power diode laser (HPDL). The findings showed a marked difference existed in the surface condition of the concrete after HPDL treatment depending on the shield gas used. The use of O2 as the shield gas was seen to result in glazes with far fewer microcracks and porosities than those generated with either Ar or He shield gases. Such differences were found to be due to the smaller O2 gas molecules dissolving molecularly into the open structure of the HPDL generated glaze on the OPC surface of concrete and react with the glass network to increase the fluidity of the melt. This in turn was also seen to affect the cooling rate and therefore the tendency to generate microcracks

The enamelling of concrete for improved performance characteristics by means of high power diode laser interaction

The contemporary 120 W high power diode laser (HPDL) has been successfully used for the first time to fire an enamel glaze onto the ordinary Portland cement (OPC) surface of concrete. The enamel glazes were generated with laser power densities as low as 1 kW/cm2 and at speeds of up to 780 mm/min, yielding a possible maximum coverage rate of 0.34 m2/h. The enamel glazes were typically 750 m in thickness and displayed no discernible microcracks or porosities. Owing to the wettability characteristics of the OPC, it proved necessary to laser treat the OPC surface prior to firing the enamel. Mechanical testing of the HPDL fired enamel glazes revealed that the average rupture strength was 2.8 J, whilst the rupture strength of the untreated OPC surface was some 4.3 J. The average bond strength of the glaze was recorded as 2.4 MPa as opposed to 6.3 MPa for the untreated OPC. The HPDL fired enamel glazes exhibited exceptional wear and corrosion resistance, wearing by only 3.3 mg/cm2 after 8 h and showing no discernible morphological or microstructural changes when exposed to acid, alkali and detergent. In contrast, the untreated OPC surface was attacked almost immediately by the reagents used and was worn by 78 mg/cm2 after 8 h. In addition, the HPDL fired enamel glaze afforded the concrete bulk complete resistance to water absorption. The findings of life assessment testing revealed that the HPDL fired enamel glaze effected an increase in the wear life of the concrete by 4.5 to 52.7 times over an untreated OPC surface, depending on the corrosive environment

Dasein, The Early Years: Heideggerian Reflections on Childhood

Like most philosophers, Heidegger gave little attention to childhood, but his philosophical emphasis on pre-reflective practice and understanding seems uniquely qualified to help make sense of a child’s experience and development. Moreover, it seems to me that many central Heideggerian concepts are best defended, exemplified, and articulated by bringing child development into the discussion. A Heideggerain emphasis on pre-theoretical world-involvement opens up a rich array of phenomena for studying child development, which can improve upon standard theories that have over-emphasized exclusive conditions or criteria. I begin by laying out some basic features of Heidegger’s conception of being-in-the-world as a preparation for understanding the world of the child. Then I will briefly discuss some of Heidegger’s remarks on childhood, followed by some reflections on language acquisition and the correlation of anxiety and meaning