Piotr Klemm

Some experimental results of laser beam interaction with surface layer of brick

Abstract Preservation of cultural heritage is gaining increasing attention all over the world. Restoration of ancient artwork and architecture requires even more effective cleaning techniques than are currently available. Laser cleaning appears to be a suitable method for removing surface contaminants from porous materials like masonry. This paper presents some effects of laser beam interaction (ruby laser, free generation regime) with clean and contaminated surface of brick which was subjected to long term exposure to atmospheric conditions. The effects of the laser beam interaction have been examined by the optical microscopy method, scanning electron microscopy and X-ray microanalysis. The present research revealed the potential application of laser irradiation for cleaning of the surface layer from contaminants and possible modification of the chemical composition of cleaned surfaces.

Ice formation in pores in polymer modified concrete—II. The influence of the admixtures on the water to ice transition in cementitious composites subjected to freezing/thawing cycles

Abstract This paper presents results which are part of a larger study on the influence of two admixtures (methyl hydroxy ethyl cellulose, MHEC, and polyvinyl acetate, PVA) on properties of water contained in pores and capillaries of cementitious materials subjected to freezing and thawing. An attempt has been made to explain some aspects of frost deterioration based on the Everett and Hynes model of phase transition. The Differential Scanning Calorimetry technique was used to record the process of water to ice transition in cementitious composites, which were initially subjected to different curing conditions including freezing and thawing. A study of the phase transition of water in polymer modified concrete revealed variations in the ice concentration depending upon the mix composition and number of freezing and thawing cycles. It has been found that admixtures have strong effects on the phase transition particularly after prolonged exposure to alternate freezing and thawing.

The effects of the alternate freezing and thawing cycles on the pore structure of cementitious composites modified by MHEC and PVA

Abstract Deterioration of mortars by weathering is usually of great importance and is brought about by the disruptive action of alternate freezing and thawing of free water within the material. As it appears that applications of methyl hydroxy ethyl cellulose (MHEC) and polyvinyl acetate (PVA) are very beneficial in improving frost resistance, special attention has been paid to observing the changes in microstructural features of polymer modified composites exposed to the destructive effects of water and low temperature. The presence of both admixtures in normally cured composites has been found to have a significant effect on their microstructure. The microstructure is mostly determined by the quantity of MHEC used, as it provides water retention. The application of PVA slightly affects the pore size distribution, significantly improving the adhesive properties of composites. The present research revealed an interrelationship between the quantity of admixtures used and the micro-structural features of composites subjected to freezing and thawing. The mercury intrusion porosimetry results suggest the significant effect of rehydration process with respect to the damage caused by the action of crystallised ice.

Non-contact methods of measuring moisture concentration in external layers of building partitions. I—The influence of geometrical microstructure on the kinetics of moisture condensation on glass surfaces

Abstract This paper presents the results of the larger study on the potential application of laser radiation for the detection of phase transition processes. The proposed experimental method allows a dynamic study of the phenomena without mechanical intervention. This seems to be the best practical solution particularly when the access for the other methods is very restricted. The investigations give an evidence of the strong relationships between the rapid growth of water vapour condensate and the roughness of the surface. Condensation process therefore can be modified by a careful design of the geometrical structure of surface.

Non-contact methods of measuring moisture concentration in external layers of building partitions. III-Water vapour condensation on the cementitious surfaces

Abstract This paper presents the results of the larger study into a potential application of laser radiation for the detection of phase transition processes in low temperatures occurring on the surface layers of cementitious materials. An attempt was made to identify relationships between the environmental conditions—temperature and air humidity, and the selected parameters of the reflected light. Onset of the condensation process and formation of water microdrops on the surface of the material leads to the phase displacement of individual laser rays, which are represented by different speckle images. Although the analysis of parameters of the reflected light are very difficult in the case of porous materials because of highly developed roughness of the surface structure it has been proved that a dynamic study of the phase transition phenomena can be successfully carried out without mechanical intervention.

Ice formation in pores in polymer modified concrete—I. The influence of the admixtures on the water to ice transition

Abstract This paper reports results from a larger study on the influence of two admixtures (methyl hydroxy ethyl celullose, MHEC and polyvinyl acetate, PVA) on properties of water contained in pores and capillaries of cementitious materials subjected to freezing and thawing cycles. The Differential Scanning Calorimetry technique has been found to be particularly useful in evaluating the amount of heat that is involved as material undergoes either an endothermic or an exothermic transition. An attempt has been made to explain some aspects of phase transition based on the Everett and Hynes model. Test results have shown that the lowest values of ice concentration were recorded for composites which had the lowest MHEC contents and finer microstructure.

The Effects of Laser Cleaning Process on Geometrical Microstructure of Cementitious Composites

The paper presents part of the larger study on laser cleaning process. A special emphasis is placed on the modification of geometrical microstructure of cementitious composites resulting from cleaning process. A wide range of samples characterised with different internal microstructures, surface roughness, and moisture content were subjected to laser cleaning process, and a subsequent assessment. Removal of mortar, cracks and glassy patches were the characteristic features of all laser-cleaned areas. Systematic analysis of surface modifications resulting from laser cleaning confirmed a strong relationship between initial roughness of surfaces and their end conditions. An increase in initial surface roughness leads to more pronounced alterations in roughness and reduced tendency towards crack formation.