Ceramics-Silikáty 53, (4) 303 - 309 (2009)

Porous clay ceramic materials are subject to an ageing process which leads to moisture expansion. The irreversible moisture expansion value is usually determined with the use of time-consuming standard tests that require samples 20 cm in length. An advantage of dilatometric method that samples 2.5 cm in size can be measured. Using this method, we determined the irreversible moisture expansion values of samples of historical roof tiles of various ages. The procedure analyzes the course and the shape of the curves and reveals whether the volume changes result from the moisture expansion process. Rehydrated water is evolved within the interval 150-500°C. In addition, the correlation between the mineralogical composition and the irreversible expansion value has been studied. Materials containing mullite fired at temperatures above 1000°C show low values, while samples with high porosity and containing no mullite fired at temperatures below 1000°C show high values. Material containing gypsum exhibits the opposite effect – the tested fragments shrank, rather than expanded.