Monument Future. Siegfried Siegesmund

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      Wedekind, W., Ruedrich, J. (2006) Salt-Weathering, Conservation Techniques and Strategies to protect the rock cut Facades in Petra/Jordan. In: R. Fort, M. Álvarez de Buergo, M. Gomez-Heras & C. Vazquez-Calvo (Eds.). Heritage, Weathering and Conservation. Taylor & Francis, London, p. 261–268. terscience, New York.

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       NOTES OF A BOWING BEHAVIOR ON LIMESTONE

Luís Sousa^1,2, Johanna Menningen³, Siegfried Siegesmund³

      IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.

       – PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –

       VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.

      1 University of Trás-os-Montes e Alto Douro, Quinta de Prados, 5001-801 Vila Real, Portugal

      2 Centro de Geociências da Universidade de Coimbra, Coimbra, Portugal

      3 Geoscience Centre of the Georg August University Göttingen, Germany

       Abstract

      Eleven Portuguese limestones were evaluated regarding their bowing behavior. Only one variety showed meaningful bowing values under thermohydric conditions. The slabs of this variety, named Valverde, show a constant rate of deformation and reach bowing values of about 8 mm/m. While under dry heating cooling cycles no deformation was observable, the addition of water lead to increasing deformation values. On the contrary, alternating dry and wet cycles enable the limestone samples to recover during the dry cycles. Only continuously wet conditions imprint permanent bowing.

      Petrographic observations and dilatometry tests allow to identify several stylolites filled with iron oxides as a possible reason for this behavior. These irregular fractures open under thermohydric conditions. Beyond a certain opening limit, the asperities inhibit the minerals to retake the initial position and deformation will be permanent. Therefore, this stone should not be used under wet conditions combined with higher temperatures. Those conditions would cause a bowing behavior as reported in several cases.

      Keywords: limestone; bowing; petrographic properties

       Introduction

      Bowing 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), СКАЧАТЬ