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

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

Relationship of Local, State, and Federal Participation in Public Library Development

published or submitted for publicatio

A subquadratic algorithm for constructing approximately optimal binary search trees

An algorithm is presented which constructs an optimal binary search tree for an ordered list of n items, and which requires subquadratic time if there is no long sublist of very low frequency items. For example, time = O(n^1.6) if the frequency of each item is at least ε/ n for some constant ε > 0.A second algorithm is presented which constructs an approximately optimal binary search tree. This algorithm has one parameter, and exhibits a tradeoff between speed and accuracy. It is possible to choose the parameter such that time = O(n^1.6) and error = o(l)

Length limited coding and optimal height-limited binary trees

A new O(nL)-time algorithm is given for finding an optimal prefix-free binary code for a weighted alphabet of size n, with the restriction that no code string be longer than L. An O(nL logn)-time algorithm is given for the corresponding alphabetic problem problem, which is equivalent to optimizing a dictionary of n words, implemented as a binary tree of height

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

Augmentation of the mechanical and chemical resistance characteristics of an Al2O3-based refractory by means of high power diode laser surface treatment

Augmentation of the wear rate and wear life characteristics of an Al2O3-based refractory within both normal and corrosive (NaOH and HNO3) environmental conditions was effected by means of high power diode laser (HPDL) surface treatment. Life assessment testing revealed that the HPDL generated glaze increased the wear life of the Al2O3-based refractory by 1.27 to 13.44 times depending upon the environmental conditions. Such improvements are attributed to the fact that after laser treatment, the microstructure of the Al2O3-based refractory was altered from a porous, randomly ordered structure, to a much more dense and consolidated structure that contained fewer cracks and porosities. In a world economy that is increasingly placing more importance on material conservation, a technique of this kind for delaying the unavoidable erosion (wear) and corrosion that materials such as the Al2O3-based refractory must face may provide an economically attractive option for contemporary engineers

Determination of the absorption length of CO2, Nd:YAG and high power diode laser radiation for a selected grouting material

The laser beam absorption lengths of CO2, Nd:YAG and a high power diode laser (HPDL) radiation for a newly developed SiO2/Al2O3-based tile grout have been determined through the application of Beer-Lambert’s law. The findings revealed marked differences in the absorption lengths despite the material having similar beam absorption coefficients for the lasers. The absorption lengths for the SiO2/Al2O3-based tile grout for CO2, Nd:YAG and HPDL radiation were calculated as being 23211 m, 1934 m and 1838 m respectively. Moreover, this method of laser beam absorption length determination, which has hitherto been used predominantly with lasers operated in the pulsed mode, is shown to be valid for use with lasers operated in the continuous wave (CW) mode, depending upon the material being treated

Trend Spotting: NAFTA Disputes After Fifteen Years

Cross-border investment disputes have supplanted trade disputes as the main focus of legal actions under the North American Free Trade Agreement (NAFTA), according to this study. The author finds a growing number of these investment disputes entail challenges by American investors against Canada's provincial, as opposed to federal, laws and regulations. So important constitutional issues need clarifying between Ottawa and the provinces. He notes as party to the treaty, Ottawa must carry the ball in court but who is really responsible? Who pays when the provinces or municipalities run afoul of Ottawa’s multilateral commitments?International Policy, NAFTA, trade remedy disputes, Canadian federal government, Canadian provincial governments