Analysis of the bowing phenomena on stone slabs

The bowing of stones has been known for many years on slabs used in memorial monuments. In the last twenty years it has also been observed on a number of marble claddings of buildings. This paper illustrates some methods for analysis of this phenomenon and the results obtained until now. The first step of the study concerned the collection of case history of buildings with marble claddings. A second step focussed on laboratory tests on three marbles with different characteristics and different tendency to bow. The tests performed were based on the measurements of strains (both elastic and plastic) in the conditions of flexure test under constant moment. A dynamic load bending test (ten cycles of loading and unloading at a maximum stress level equal to ca. 50% of the expected flexural strength) and a Long term bending test (specimens with reduced thickness and loaded at the same stress level for about seven days) were performed. The results of all test indicated that stones that could bow on the facades and on memorial monuments show higher residual strains than stones that do not bow. That implies that a creep phenomenon may affect different stones in a different way.