Salt bursting tests on volcanic tuff rocks from Mexico

Abstract

During the pre-colonial period all the architectural constructions of the Maya and the later Aztec culture were made from different types of rocks available in the nearby surroundings of the settlements. Later, the architecture characterizing the Spanish colonization utilized volcanic tuff rocks for ashlars and masonry facades. Volcanic tuffs were used in large quantities and are still the main natural building rock used in most of the country. Tuffs are mostly soft and porous rocks that can be easily cut and reworked. They are, however, very susceptible to the effects of weathering, especially the deterioration caused by salt crystallization. Seventeen volcanic tuff samples from Mexico used as natural building stones were studied. These tuffs show highly variable compositions and different porosities and textural properties as well as very different behaviors in regard to salt crystallization. The petrographic, petrophysical, mineralogical and geochemical properties of the 17 samples were analyzed before and after a large number of salt bursting tests in order to try and determine the main factors leading to the weathering caused by salt crystallization. Some factors appear to have a real importance in regard to the resistance against salt crystallization. Two of the most important are the water vapor diffusion (μ value) and the pore radii distribution; however, microporosity also becomes a relevant factor for rapid salt destruction if it reaches more than 50 % of the pore volume. All these effects related to the salt crystallization are dependent on the presence of water in any form, so the climatic conditions must also play a principal role.