Monument Future. Siegfried Siegesmund
Чтение книги онлайн.
Читать онлайн книгу Monument Future - Siegfried Siegesmund страница 87
Название: Monument Future
Автор: Siegfried Siegesmund
Издательство: Автор
Жанр: Документальная литература
isbn: 9783963114229
isbn:
Petrophysical properties and weathering behavior
The petrophysical properties and weathering behavior of the sandstones were determined in accordance to the German industrial norms parallel (X-direction) and perpendicular (Z-direction) to the bedding. For further information see Siegesmund and Dürrast (2011). Table 1 gives an overview of the laboratory results.
In general, the sandstones can be divided into 213group one (S1, S3) and group two (S2, S4) of similar petrophysical properties and weathering behavior. Group two is characterized by higher porosities (> 20 vol%) and bulk densities around 2.0 g/cm3. Group two also shows unimodal pore radii distributions with large ratios of capillary pores (> 93 %) and mean pore radii between 0.9 and 5.7 µm. Group one (S1, S3) on the other hand, shows mean pore radii of 0.3–0.5 µm and contains considerable amounts of micropores (< 48 %). Up to nine times higher capillary water absorption (< 9 kg/m2√h) and lower resistance against water vapor diffusion in group two indicate better pore connection than in the sandstones S1 and S3 of group one (Tab. 1). The saturation coefficient S, as an indication of the materials’ frost resistance (Hirschwald 1912), classifies S1, S3 and S4 as frost resistant and S2 as uncertain.
Table 1: Petrophysical properties and weathering behavior of the four analyzed sandstones.
Regarding the moisture expansion, both groups show distinct differences when subjected to water (Tab. 1). While group two (S2, S4) shows barely any expansion (< 0.06 mm/m), the sandstones of group one (S1, S3) expand up to 0.2 mm/m. However, the hydric expansion values of the investigated sandstones can be generally considered low when compared to other sandstones (Siegesmund and Dürrast 2011).
The response to temperature changes is high in all investigated sandstone samples. Under dry conditions the sandstones expand about 0.8 mm/m. This expansion is increased up to 1.1 mm/m (S1, S3) when heating under wet conditions (Tab. 1). The average thermal expansion coefficients α range between 11 and 13 × 10–6 K–1 and can be considered very high. These high values, however, are not surprising, since quartz characteristically possesses a high thermal expansion coefficient and the investigated sandstones show high compositional maturity. The residual strains are considerably low under dry conditions and do not exceed 0.2mm/m under wet conditions.
The strength of the rock material is proportional to their dynamic modulus of elasticity (Young’s Modulus), which can be determined via the ultrasonic velocity. The ultrasonic velocity with up to 3.8 km/s as well as the Young’s Modulus with up to 32 GPa are significantly higher in group 1, meaning S1 and S3 possess a higher rock strength. In comparison, group two (S2, S4) shows ultrasonic velocities of 2.5 km/s and Young’s Moduli of up to 13 GPa.
Under laboratory conditions the sandstones show moderate resistance towards salt attack. After 30 cycles of salt bursting test (standard DIN EN 12370), the sandstones show a distinct darkening of their color tone and suffer minor material loss in the form of flaking and scaling (Fig. 7). Only S1 shows a constant loss of material in the form of bursting of edges and smaller components (Fig. 7a).
Figure 7: Discoloration and material loss of sample cubes S1–S4 after 30 cycles of salt bursting test.
Summary
The studied monoliths show diverse, partly exposure-specific weathering forms. Under laboratory 214conditions, the negative effects of thermal and thermohygric expansion were identified and are in accordance with the field observations. Water did show to increase the negative effect of thermal expansion on the investigated sandstones. Also its function as a transport medium has to be taken into account. The in-situ investigation showed severe damages associated with salt crystallization, which could be reproduced under laboratory conditions to a lesser extent. Possible protective measures for the future could be temporary roof constructions during seasons of high solar radiation and temperature or a protective planting of trees, which would be a permanent, but more natural solution. Nevertheless, individual monoliths should be considered for conservational treatment due to the high degree of weathering. Desalination and repairs with stone replacement mortars as well as measures to minimize the future salt input into the stone can be crucial. Regarding the origin of the monolith source material, the data from the in-situ and petrographic investigations, point towards a sandstone layer in the Paja Formation as origin of the sandstones S2 and S3. Therefore, further investigation should concentrate on the residual sandstone boulders covering the Paja Formation in the vicinity of the park.
Acknowledgements
We would like thank M. Silva Celis, director of the archaeological park Monquirá, for supporting our work as well as C. Gross for helping with the petrographical descriptions.
References
Etayo-Serna, F., 1968. Sinopsis Estratigrafica de la region de Villa de Leiva y zonas proximas. Boletín de Geología 8.
Hirschwald J (1912) Die Prüfung der natürlichen Bausteine auf ihre Wetterbeständigkeit. W. Ernst & Sohn, Berlin.
Öcal, A. D.; T. Cramer; S. Siegesmund, 2009. Caracterización de agentes del deterioro de los monolitos de piedra arenisca del Infiernito – Colombia, en 2do. Congreso Argentino y 1ro. Latinoamericano de Arqueometría 6–8 de julio de 2007, Tulio Palacios et al. – eds. – Buenos Aires: Comisión Nacional de Energía Atómica – CNEA, 2009, pp. 413–419.
Patarroyo Gama, P., 2008. La Formacion Ritoque en la zona de Vélez (Santander-Colombia). Geología colombiana 33, 109–110.
Renzoni, G., Rosas, H., Etayo-Serna, F., 1983. Mapa Geológico de la Plancha 171, Duitama, esc. 1:100.000. Ingeominas, Bogotá.
Siegesmund, S. and Dürrast, H. (2011), Physical and mechanical properties of rocks. In Siegesmund, S. and Snethlage, R. (Eds.), Stone in architecture, Springer, pp. 97–225.
Silva Celis, E. (1983) Descubrimiento Arqueológico en Villa de Leiva. Boletín de Antropología 5 (17–19), pp. 235–250.
Simón, P. 1981. Noticias Historiales de las Conquistas de Tierra Firme en las Indias Occidentales; Biblioteca del Banco Popular, Bogotá.
215
EVALUATION OF EFFECTIVE COMPRESSION STRENGTH OF NATURAL STONE BY DRILLING RESISTANCE MEASUREMENTS
Stephan Pfefferkorn1, Christoph Franzen2
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 СКАЧАТЬ