Читать книгу Monument Future - Siegfried Siegesmund - Страница 164

Zeolites have an important influence on the weathering behaviour of natural building stones. Korkuna et al. (2006) found very small pore sizes for zeolite-rich samples (< 2 nm) resulting in a high specific surface area. The specific surface area, along with the pore size and connectivity of the pores is a controlling factor for water transport and retention in porous rocks and has a great influence on values like capillary water uptake, water vapor diffusion and hygroscopic water sorption (Siegesmund and Dürrast 2011).

Hydric dilatation can cause a significant volume change in tuff rocks and is therefore an important weathering factor. Reasons for hydric expansion may be the presence of swellable clay minerals or a large percentage of micropores (e. g. Gonzales and Scherer 2004). The swelling of natural building stones with a high percentage of micropores may be explained by the process of disjoining pressure, but the process is still under discussion (e.g. Ruedrich et al. 2011; Wedekind et al. 2013; Pötzl et al. 2018a; Pötzl et al. 2018b).

Zeolites adsorb and desorb water molecules reversibly (Di Tchernev 1978). They are therefore able to store heat during desorption and give it back to the environment during adsorption. Between 0 °C and 90 °C zeolites counter the expected thermal 120expansion because of shrinkage due to reversible water loss (Colella et al. 2001). Zeolites accordingly have an influence on the thermal expansion behavior of tuff rocks.

In this study zeolite and clay-rich tuff rocks from the states of Oaxaca in Southern Mexico and Queretaro in Central Mexico were investigated and compared with zeolite-free samples.