The effect of salt crystallization on degradation of volcanic building stones by sodium sulfates and sodium chlorides

Abstract

Volcanic rocks cropping out in the north-northeast of Afyonkarahisar (Turkey) are extensively used as building stones for the construction of historical buildings with structural and architectonic purposes. Three building stones, including two tuffs and an andesite, were examined in the current research. The scope of this article was to study the decay mechanisms of these porous building stones by salt. For this purpose, laboratory studies were carried out in two stages. First, the main characterization analysis of the tested building stones was performed. The main technical values and parameters such as mineralogical–petrographic (polarizing microscope, XRD and SEM), chemical (XRF) and mechanical–physical properties were studied. Moreover, this study also included pore size distribution and capillary water absorption of the building stones, while their durability was investigated by means of salt crystallization tests according to TS EN 12370. Weathering tests were carried out by applying immersion–drying cycles with water containing sodium sulfate or sodium chloride. The structural changes of the building stones after the salt crystallization tests were investigated by SEM observations and ultrasonic wave measurements, while the strength properties were determined by uniaxial compressive strength tests. The highest values of dry weight loss were observed in the Ayazini tuff sample and andesite whereas the Seydiler tuff had the lowest value. The uniaxial compressive strength was 16.37% lower in the weathered samples (sodium sulfate test) compared to the fresh samples of andesite. As a result, only the Ayazini tuff was not durable and deteriorated in the environment containing sodium sulfate.