Interpreting sulfated crusts on natural building stones using sulfur contour maps and infrared thermography

Abstract

In this study, the effect of sulfation due to air pollution in the portals of the Ince Minareli Madrasa built of pyroclastic rocks and the Karatay Madrasas (Konya, Turkey) built of marble was investigated. Since the sulfur element in sulfate salts is represented as sulfate, the sulfur contour maps (SCM), obtained by transferring the portable X-ray fluorescence measurements onto the orthophotographs, also show the sulfated crust formation, distribution and anomaly regions on the portal surfaces. Additionally, the anomaly regions originating from the difference in thermal conduction between the sulfated crusts and portal surfaces on thermal camera images were determined, and they were observed to be compatible with the anomaly regions on SCM. However, the size of this correlation depends on the chemistry of the building stone and the thickness of the sulfated crusts. Then, it was determined that the anomaly regions on SCM were distributed in relation to the washing out of sulfated crusts by rainfall and capillary moisture content. Accordingly, portal surfaces were divided into three as the sheltered, washing and capillary regions. Consequently, it was demonstrated that the sulfation effect due to air pollution on historical building surfaces which have appropriate rock chemistry can be determined by non-destructive testing methods like using the SCM supported by infrared thermography. The fact that the method is simple and repeatable and is easily applicable to other buildings was considered as the most important success of the method.