Changes on physical and mechanical proprieties related to salts crystallization weathering in natural building stones: effects of microtextural and microstructural features

The main aim of this research is to highlight the effects of salts crystallization on physical and mechanical proprieties of natural building stones in consideration of porosimetric and petrographic features. In fact, these latter features strongly affect physical and mechanical behaviour of stones [1-4]. In particular the research is focused to the case of coarse grained calcarenites in which the complex porous structure is suitable for this study. Furthermore, they are widely used as building and replace stones in Cultural Heritages. Even if a large bibliography exists about durability esteem procedure for building stones[5], really a few examples of integrate study on both microtextural, microstructural and physical-mechanical proprieties changes due to salts weathering are available [6-7]. The knowledge of the relationship among these features allows to better understand the behaviour of the stones, especially in the framework of engineering applications and restoration works. In order to achieve the goals of this work, a multidisciplinary approach has been applied with the aim at outline the relation between minero-petrographic and physical mechanic characteristics in describing the degradation style of a Sicilian coarse grained calcarenite, namely Sabucina Stone [8-9]. Comparative porosimetric measurements, water absorption and mechanical resistance tests have been carried out before and after artificial weathering processes, allowing to estimate changes in the proprieties of the stone. In particular, the microtextural and microstructural modifications due to the salt crystallization induce a worsening of the engineering properties of the studied rock as highlighted by the decrease of the real density and the Uniaxial Compressive Strength (UCS) values. Finally, the obtained results allow us to establish interesting correlation between the intensity of degradation processes and the textural, structural and engineering parameters acquired. REFERENCES [1] Tugrul, A. & Zarif I.H.: Correlation of mineralogical and textural characteristics withengineering properties of selected granitic rocks from Turkey. Engineering Geology 51(1999), 303-317 [2] Andriani, G.F.& Walsh N.: Physical properties and textural parameters of calcarenitic rocks: qualitative and quantitative evaluations. Engineering Geology 67(2002), 5-15. [3] Tamrakar, N. K. et al.: Relationships among mechanical, physical and petrographic properties of Siwalik sandstones, Central Nepal Sub-Himalayas. Engineering Geology 90(2007), 105-123. [4] Zorlu, K. et al.: Prediction of uniaxial compressive strength of sandstones using petrography-based models. Engineering Geology 96 (2008), 141-158. [5] Yu, S. & Oguchi, C.T.: Role of pore size distribution in salt uptake, damage, and predicting salt susceptibility of eight types of Japanese building stones. Engineering Geology 115 (2010), 226 -236. [6] Tugrul A.: The effect of weathering on pore geometry and compressive strength of selected rock types from Turkey. Engineering Geology 75(2004), 215-227. [7] Sousa, L. M.O. et al.: Influence of microfractures and porosity on the physico-mechanical properties and weathering of ornamental granites. EngineeringGeology 77 (2005), 153-168. [8] Bellanca, A. et al.: Petrografia, geochimica e riferimenti all'impiego storico delle calcareniti plioceniche in Sabucina, Sicilia centrale. Mineralogica et petrographicaacta 42(1999), 193-210. [9] Raneri, S. et al.: X-ray computed micro-tomography to study the porous structure and degradation processes of a building stone from Sabucina (Sicily), European Journal Mineralogy, in press.