Pore structure and durability of Portuguese limestones: a case study

Abstract

Exposed stone surfaces containing complex systems of pores, fractures and grain boundaries provide the surfaces where chemical, physical and biological deterioration processes take place. The pore space represents the preferred area for physical, chemical and biological weathering processes. It plays a significant role in the behaviour of porous materials. A full understanding of pore-channel network morphology, size and connectivity is important in stone decay assessment and conservation works. A contribution to the understanding of the role played by the pore system in controlling fluid-related properties and resistance to salt crystallization of limestones is presented. Optical microscopy, scanning electron microscopy (SEM) and mercury injection porosimetry (MIP) were used to characterize the pore structure of two Portuguese dimension stones (‘Semi-rijo’ and ‘Moca-Creme’) widely used for pavements and the cladding of buildings. Fluid migration physical tests (open and free porosity, capillary imbibition, and Hirschwald coefficient) were also performed, according to European (EN 1925:1999; EN 1936:1999) and French (N FB 10-504:1973) Standards. The resistance to salt crystallization was determined using European Standard EN 12370:1999. An integrated analysis facilitated comparison between durability results with stone pore network characteristics, fluid transport properties and petrographical features, suggesting the influence of available porosity and bedding.

Limestones under salt decay tests: assessment of pore network-dependent durability predictors

“…Gauri and Bandyopadhyay present an equation that relates crystallisation pressure of a given salt to porosity of the stone (considering also the volume of the sample, salt absorption and characteristics of the salt such as molar volume, solubility and density). Several laboratory studies have found that higher porosity would promote lower durability in limestones (Skoulikidis et al 1996;Birginie 2000;Nicholson 2001;Cardell et al 2003;Figueiredo et al 2010b) as well as on other rocks such as marbles (Skoulikidis et al 1996) and granites (Rivas et al 2000;Sousa et al 2005). However, some authors have found lower porosity stones presenting lower durability.…”

Susceptibility of Limestone Petrographic Features to Salt Weathering: A Scanning Electron Microscopy Study

“…This was related to difficulties in performing the capillary imbibition tests on the travertine specimens, as explained by the heterogeneous character of this rock type (limiting the access of solutions to the pore space of these limestone specimens). Figueiredo et al (2010 a , 2010 b ) highlighted the positive association of mass loss with porosity in these grainstones, as well as the influence of textural heterogeneities (specially in Moca Creme). In the analyses of the macroscopic erosion patterns of the specimens and following the terminology of Angeli et al (2007), Alves et al (2009) indicated that these grainstones presented a generally homogeneous decay behavior with overall erosion of edges and corners (shape controlled), whereas the travertine sample showed heterogeneous patterns that these authors related to the presence of clay minerals.…”

“…The grainstones are from a Bathonian (Middle Jurassic) formation [Direcção-Geral de Geologia e Minas (DGGM), 1983–1985; Instituto Geológico e Mineiro (IGM), 1995; Manuppella et al, 1985] located about 100 km north of Lisbon (Portugal). These grainstones are classified (Figueiredo et al, 2010 a , 2010 b ) as fossiliferous pelmicrosparite/grainstone (Semi-rijo samples) and as biopelintrasparite/grainstone (Moca Creme samples). Semi-rijo presents rare rounded bioclasts (allochemical components size ranging from 0.08 to 1.6 mm), whereas Moca Creme is richer in bioclasts and has a coarser texture with pelloids ranging from 0.03 to 0.08 mm and bioclasts with, in general, a centimetric size.…”

“…Regarding characteristics of the pore space of these limestones, data from Figueiredo et al (2010 a , 2010 b ) and from Alves et al (2011) indicate values of open porosity between 11.15 and 12.44% with an average of 11.44% for Semi-rijo, between 12.47 and 12.72% with an average of 12.57% for Moca Creme, and between 8.21 and 14.31% with an average of 10.56% for travertine. Semi-rijo and Moca Creme samples present mercury injection porosimetry curves that can be considered as corresponding to unimodal pore structures (Figueiredo et al, 2010 a , 2010 b ). Travertine samples typically present a multimodal curve linked to petrographic heterogeneity of the travertine (see Alves et al, 2009, 2011).…”

Alteration Processes and Deterioration Phenomena of Faience Tiles in the Complex of King Djoser at Saqqara, Egypt

“…Limestone supported walls of faience tiles also suffer from salts crystallization. Salts may be carried into the stone with groundwater by capillary rise (Figueired et al, 2010) or may be dissolved from the mortar joints, or result from chemical reaction between atmospheric pollutants (especially SO2) and minerals (such as calcite (CaCO3) in the limestone). If salts precipitated beneath the material of surface (a phenomenon called subflorescence or cryptoflorescence) severe damage can be induced (Espinosa-Marzal et al, 2010).…”