Characterization of swelling in clay-bearing stone

Many sedimentary rocks contain clays that cause differential swelling upon exposure to moisture, and the resulting internal stresses are blamed for the deterioration of buildings and monuments. To predict the likelihood of damage from this mechanism, it is necessary to characterize the magnitude of the swelling and the mechanical properties of the stone. Stones that swell also exhibit viscoelastic behavior, probably owing to sliding of the clay layers. In this paper we discuss the characterization of the relaxation and swelling behavior and the estimation of stresses resulting from swelling. A new method for measuring swelling is introduced, in which warping of a plate of stone is produced by wetting one side. This method is faster than the traditional direct measurement of swelling pressure, and it also yields information about the permeability and the influence of wetting on the elastic modulus. Sample results are presented for Portland Brownstone.