Читать книгу Monument Future - Siegfried Siegesmund - Страница 212
Introduction
ОглавлениеBowing behavior has been described for different rock types. Nevertheless, marble is the stone mostly prone to such a permanent deformation. The specific textural characteristics of marble together with anisotropic calcite crystal properties causes thermal strain within grain to grain contacts and originates bowing (Siegesmund et al. 2000; Siegesmund et al. 2008). Although this phenomena was described for many rock types, as for example 146even weathered granites can display bowing behavior (Siegesmund et al. 2018), there are only scarce cases reported for limestones (Siegesmund 2008).
Figure 1: Macroscopic appearance of Valverde limestone (honed surface; size of the photo: 10 cm × 10 cm).
Table 1: General characteristics and classification (according Dunham (1962) and Folk (1962)) of the selected limestones. The sample VAV is the Valverde variety.
| Sample | General characteristics | Classification |
| ALP | Grey limestone composed of a micritic groundmass (95 %) and 5 % of components | Pelagic Mudstone (after Dunham, 1962) and Micrit (after Folk, 1962) |
| ATAZ | Light cream limestone with 50 % groundmass and 50 % components | Peloidal wackestone (after Dunham, 1962) and Pelmicrit (after Folk, 1962) |
| ATCR | Cream coloured limestone with 60 % groundmass and 40 % components | Peloidal wackestone and packstone (after Dunham, 1962) and Pelmicrit (after Folk, 1962) |
| CODFV | Light grey limestone composed of 60 % groundmass and 40 % components | Ooid-peloid grainstone (after Dunham, 1962) and Oopelsparit (after Folk, 1962 |
| LIOZ | Fully recrystallized limestone composed of calcite microcrystals (sparit and microsparit) | Dolosparit (after Folk, 1962) |
| MCCT | Light cream limestones composed of 50 % groundmass and 50 % components | Bioclastic grainstone (after Dunham, 1962) and Biopelsparudit (after Folk, 1962) |
| SBM | Light cream limestone composed of 40 % groundmass and 60 % components | Peloidal grainstone (after Dunham, 1962) and Pelsparit (after Folk, 1962) |
| SBR | Light cream limestone composed of 40 % groundmass and 60 % components | Ooid grainstone (after Dunham, 1962) and Oosparudit (after Folk, 1962) |
| VAV | Light to medium grey limestone composed of 70 % groundmass and 30 % components. | Bioclastic packstone/grainstone (after Dunham, 1962) and Biosparit/Biodismicrit (after Folk, 1962). |
| VPAZ | Medium grey limestone composed of a micritic groundmass (> 90 %) and less than 10 % of components | Pelagic Mudstone (after Dunham, 1962) and Micrit (after Folk, 1962) |
| VPCR | Light grey limestone composed of 60 % groundmass and 40 % components | Bioclastic floatstone (after Dunham, 1962) and Biomicrudit (after Folk, 1962). |
For a Portuguese limestone (usually named Valverde) several stoneworkers described bowing phenomena. In order to evaluate these observations systematically, eleven limestone varities were selected and analysed: Alpinina (ALP), Ataíja Azul (ATAZ), Ataíja Creme (ATCR), Semi-rijo Codaçal (cut pararellel to the sedimentary lamination, CODFV), Lioz (LIOZ), Moca 4M (cut perpendicular to the sedimentary lamination, MCCT), Semi-rijo Branco Mais(i) (SBM), Semi-rijo Branco Real (SBR), Vidraço Azul Valverde (VAV); Vidraço Portela Azul (VPAZ); Vidraço Portela Creme (VPCR).
The limestone samples used in this study where collected in the Maciço Calcário Estremho (MCE), a Jurassic limestone massif located in the Portuguese Lusitanian Basin, with the exception of one sample (LIOZ) collected in a Cretaceous Unit near Lisbon (Silva, 2017). MCE is one of the world’s leading regions producers of limestones for ornamental purposes. The quarries develop along the hillside, with several benches, can reach depths around 50 m and are grouped in several exploitation sites. Several lithostratigraphic units are exploited and originate different ornamental varieties, from cream laminated calcarenites to grey calciclastic micritic limestones (Carvalho and Lisboa, 2018). The samples selected from MCE show this high variability.
Figure 2: Microstylolites (right in the photo) and non-disturbed matrix (left in the photo) in the sample VAV (crossed polars).
147Besides a petrographic characterization, the hydric expansion caused by moisture exposure was evaluated as well as the bowing potential and thermal expansion measurements were performed.
