First wet cycle
Blanco Macael, Lasa and Gioia have a comparable grain fabric and grain boundary geometry. According to their texture, the thermal anisotropy of Blanco Macael with a pronounced preferred orientation of the calcite crystals is more distinctive than the anisotropy of Lasa. This causes more intensive cracking and therefore a higher AE activity. The Gioia marble has a history of prior outdoor exposure. The low ultrasonic velocity before the first heating and the low AE activity can be explained by preexisting damage.
Summary
The deterioration mechanism of marble was studied by a combination of measurements of acoustic emission, ultrasonic velocity, thermal dilatation and residual strains. Four different types of marble were exposed to thermal fluctuations under dry and wet conditions. The results of the acoustic emission analysis show that the main damage arises during the first thermal treatment. This is confirmed by the development of residual strains and ultrasonic velocities in subsequent temperature cycles. Even under wet conditions acoustic methods detected no significant progression of deterioration. In contrast, under wet conditions a significant residual strain was observed. Apparently, the water prevents a complete closure of the cracks after cooling. This needs to be verified by further studies.
References
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Köhler W., 1991. Untersuchungen zu Verwitterungsvorgängen an Carrara-Marmor in Potsdam-Sanssouci. – Berichte zu Forschung und Praxis der Denkmalpflege in Deutschland. Steinschäden – Steinkonservierung 2:50–53; (Hannover)
Koch, A., Siegesmund, S., 2004. The combined effect of moisture and temperature on the anomalous expansion behaviour of marble. Env Geol 46 (3–4).
Rüdrich, J. M., 2003. Gefügekontrollierte Verwitterung natürlicher und konservierter Marmore. Dissertation. Mathematisch-Naturwissenschaftliche Fakultäten der Georg-August-Universität zu Göttingen
Tschegg, E. K., 2016. Environmental influences on damage and destruction of the structure of marble. International Journal of Rock Mechanics and Mining Sciences 89, 250–258.
191
AUTOMATIC ESTIMATION OF THE P- AND S-WAVE ONSET-TIMES IN WEATHERED SANDSTONES BY SALT CRYSTALLISATION
David Benavente1, Marli de Jongh2, Juan J. Galiana-Merino3, Concepcion Pla4, Javier Martinez-Martinez5, Martin Lee2, Maureen E. Young6
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 Department of Earth and Environmental Sciences, University of Alicante. 03690 Alicante, Spain
2 University of Glasgow, School of Geographical & Earth Sciences, University Avenue, Glasgow G12 8QQ, Scotland, UK
3 Department of Physics, Systems Engineering and Signal Theory, University of Alicante. 03690 Alicante, Spain
4 Department of Civil Engineering, University of Alicante. 03690 Alicante, Spain
5 Spanish Geological Survey. 28003 Madrid, Spain
6 Historic Environment Scotland, Forthside Way, Stirling FK8 1QZ, Scotland, UK
Abstract
In this investigation, we determined the onset of P- and S-waves considering signal pre-processing and the analysis of the recorded signals. For most stone conservation investigations, P-waves are easy to determine. However, the measurement of pure S-waves in fresh and weathered building materials presents critical experimental problems.
We recorded P- and S- waveforms in three sandstones used in the Scottish heritage. Doddington sandstone (D) is a quartz-arenite commonly used throughout Scotland and is currently utilised as a replacement stone at Jedburgh Abbey, Scotland. St. Bees sandstone (BC) is a dark-red lithic arkose and is currently used as a replacement stone at Arbroath Abbey. BC is quarried on the west coast of Cumbria, England and exhibits planar bedding. Forest of Dean (F) is a grey-green (sub)litharenite quarried in Gloucestershire and used throughout the UK, including in the restoration of Dunkeld Cathedral, Scotland. We obtained the P- and S-velocities as well as the calculation of wavelength of the P-waves in both fresh and salt weathered samples.
The recorded signals highlight that the microstructural components of rocks and their modification by salt crystallization affect the output signal. P-wave signals present a high signal/noise ratio and their arrival-times are clear. The wavelength increases with grain size and also the degree of salt crystallization. However, as grain size increases, the determination of S-wave arrival time becomes more problematic due to the contamination of S-waveforms by P-waves, a lower signal-to-noise ratio and an increase of wavelength. These difficulties are more prevalent in the weathered samples, where the manual
