Deformation of North American Marbles in Response to Thermal Cycling

Marble is one of the most popular building stones in the course of human history. For several centuries it has been used as a principle façade material because of many distinctive characteristics such as color, texture, and the ability to take a highly polished polish. In the past, marble blocks used in construction had to function as load bearing elements and were sized accordingly. However, as building technology improved with the rise of steel frame construction in the 19th century, reduced wall thicknesses became possible and façade materials no longer had the same structural responsibilities. During the mid-20th century thin panels of marble, ranging from 20-50 mm, appeared as exterior cladding on structures around the world. The permanent deformation of marble panels, commonly known as bowing, has been recognized as a serious problem worldwide. Over the past few decades numerous architects, engineers, and scientists have worked toward better understanding and preventing this phenomenon. In 2000 the EU commissioned a multi-dispensary project consortium working under the acronym TEAM (Testing and Assessment of Marble and Limestone) to create a report detailing the mechanisms behind thermal deformation and develop a better understanding of bowing potential for different marble types. For obvious reasons the report focused primarily on marbles originating from Europe. Today little published scientific analysis of the effects of repeated thermal cycles on North American marbles, more specifically Tuckahoe, Colorado, Vermont, and Georgia exists. Considering that the marbles being tested vary greatly in physical characteristics as well as mineralogical composition, the potential for thermal deformation and disintegration between them will likely be just as dissimilar. For this reason, there is an important and recognizable need for a study of this type to accurately and effectively develop preservation strategies. In this study, 30 sample disks approximately 50 mm in diameter and 10 mm in thickness were prepared from four previously mentioned marble types. Each sample base contained 10 disks treated with a heating cycle, 10 disks treated with a cooling cycle, and 10 untreated disks. The samples were exposed to 60 thermal cycles, 3 cycles a day for 20 days. The cooling cycle ranged from approximately -10° C to 28° C and the heating cycle from 30° C to 63° C. Upon completion of the thermal cycling, the samples were subjected to ultrasonic velocity and biaxial flexure strength tests. The results were compiled and conclusions were drawn as to why each marble preformed the way it did as well as whether or not the marble would be suitable for use as thin panel cladding.