Bowing of dimensional granitic stones

Abstract

Bowing is a well-known phenomenon seen in marbles used as building veneers. This form of rock weathering occurs as a result of external factors such as temperature, humidity, the system for anchoring the marble slabs or the panel dimensions. Under the same external conditions, many factors will determine the degree of deformation including petrography, thermal properties and residual locked stresses. The usual way to solve the problem of bowed marble slabs is to replace them with other materials, such as granites, in which the deformation still exists but is less common. In this study, eight ornamental granites with different mineralogy, grain size, grain shape, porosity and fabric were tested in a laboratory to assess their susceptibility to bowing. Three slabs of granite, each cut with a different orientation, were studied under different conditions of temperature (90 and 120°C) and water saturation (dry and wet) to investigate the influence of these factors together with that of anisotropy. At 90°C, only the granite with the coarsest grain size and low porosity exhibited deformation under wet conditions. At 120°C and wet conditions, three of the granites showed evident signs of bowing. Again, the granite with the coarsest grain size was the most deformed. It was concluded that the wide grain size distribution influences microcracking more than other expected factors, such as the quartz content of the rock. Also, mineral shape-preferred orientation and porosity play an important role in the bowing of the studied granites.

Granitic dimensional stones in Uruguay: evaluation and assessment of potential resources

“…The range of values obtained is comparable with those reported for magmatic rocks by Strohmeyer (2003), Hoffmann (2006), Weiss et al (2004), Siegesmund et al (2008), and Vázquez et al (2011). The mafic rocks show the lowest mean a, since these rocks show the lowest (2004) and Vázquez et al (2011).…”

“…Both commercial granites are very coarse-grained. A similar behavior was reported by Vázquez et al (2011) in three coarse-to very coarse-grained commercial granites.…”

“…The thermal expansion behavior of a dimensional stone is closely related to its bowing behavior when applied as slabs for outdoor façade cladding (Siegesmund et al 2008;Vázquez et al 2011). For bowing the same factors influencing thermal expansion are relevant: coarse-to very coarse-grained texture, mineral shape-preferred orientation and porosity (Vázquez et al 2011).…”

“…For bowing the same factors influencing thermal expansion are relevant: coarse-to very coarse-grained texture, mineral shape-preferred orientation and porosity (Vázquez et al 2011).…”

Evolution of surface properties of ornamental granitoids exposed to high temperatures

“…Some of the coarse grain sized granites were seriously damaged (although some measurement were still possible) such as AP, ER and RP. Others were completely disintegrated, such as GM and R, two red granitoids featuring a porphyritic texture with alkali feldspar from 1-1.5 cm in GM and up to 4-6 cm in R. Even if alkali feldspar thermal expansion in not high (4.5 Â 10 À6 /°C) and isotrope, is has been proved that their size and proportion play an important role in their deformation, and that stresses usually are concentrated in their grain boundaries [28,49]. T granitoid also appeared totally disintegrated after heating to 600°C.…”