A Thermographic Survey for the Monitoring of Moisture in Porous Stone

POROUS STONE N.P. Avdelidis, E.T. Delegou, and A. Moropoulou 1 IRT & Materials Consultancy, Volos, Greece; 2 National Technical University of Athens, Athens, Greece Abstract: In this work, infrared thermography was employed as a monitoring technique during water capillary rise tests on a choice of porous stones in the laboratory, as well as in situ on a cleaned porous stone surface of a historic building. While the emissivity values of the investigated materials were considered for the thermographic survey, other investigative techniques, such as mercury intrusion porosimetry and water sorption analysis for studying the stone in terms of their microstructure and isothermic behaviour respectively, were additionally used for the laboratory investigation on quarry samples. Results, such as water absorption coefficient and percentage, total porosity and isothermic behaviour were presented and discussed, in an attempt to explain the thermal images from the capillary rise tests. Furthermore, correlation between the thermal contrast and the imbibed water percentage for each sample obtained from the capillary rise tests was also presented in an attempt to show how powerful the action of water inside a porous stone is. Lastly, an in field thermographic survey on a cleaned historic stone surface, using a wet micro blasting method, was also carried out. Representative samples were collected from the investigated surface with the intention of studying their microstructure by means of mercury intrusion porosimetry and water sorption analysis. Introduction: The infrared inspection of buildings for heat loss was one of the first commercial uses for thermography [1]. Since then, the use of infrared thermography in monitoring of buildings, monuments and large structures has been extensively and effectively used. Published work in the field of building thermography [2-5] has been carried out using both thermographic approaches. Qualitative, as well as, quantitative analysis (employing usually the active approach) has been attained. Together with the use of thermography in the inspection of electrical and mechanical installations, the building area is considerably acknowledged [6]. In this research study, infrared thermography was used for the assessment of moisture [7] in porous stones in the laboratory; their porous nature was also investigated in terms of their microstructure. Furthermore, their emissivity values [8] were determined in the laboratory and were considered for the interpretation of the thermal images obtained during monitoring of the water capillary rise tests. An in field thermographic survey on a cleaned historic stone surface, using a wet micro blasting method, was also performed. Characteristic samples were collected from the stone surface in order to examine their microstructure by means of mercury intrusion porosimetry and water sorption analysis.