Siegfried Siegesmund - Monument Future

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.

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.

Kaiser, J., 1950. Untersuchungen über das Auftreten von Geräuschen beim Zugversuch. Dissertation. Technische Hochschule München

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.

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David Benavente 1 , Marli de Jongh 2 , Juan J. Galiana-Merino 3 , Concepcion Pla 4 , Javier Martinez-Martinez 5 , Martin Lee 2 , Maureen E. Young 6

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.

1Department of Earth and Environmental Sciences, University of Alicante. 03690 Alicante, Spain

2University of Glasgow, School of Geographical & Earth Sciences, University Avenue, Glasgow G12 8QQ, Scotland, UK

3Department of Physics, Systems Engineering and Signal Theory, University of Alicante. 03690 Alicante, Spain

4Department of Civil Engineering, University of Alicante. 03690 Alicante, Spain

5Spanish Geological Survey. 28003 Madrid, Spain

6Historic Environment Scotland, Forthside Way, Stirling FK8 1QZ, Scotland, UK

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 picking of the onset-time becomes more difficult and time-consuming. In general, the automatic method obtains S-wave values slightly lower than the manual method and their discrepancies are, on average, lower than 5 %.

Keywords: Wavelet analysis, Building stones, Salt weathering, Primary wave velocity, Shear wave velocity Ultrasound, Non-destructive testing

These non-destructive methods based on elastic wave measurements are commonly used in stone conservation investigations in both laboratory and field experiments. The study of compressional and shear wave velocities is considered a reliable method of determining the elastic, physical-mechanical, and durability properties of studied samples. Elastic wave velocities are frequently investigated either individually or in combination. The compressional or primary (P) wave velocity, V p, (also termed as ultrasonic pulse velocity) is a frequently studied parameter that is simple to measure in the laboratory. In addition, V pis also used as an indicator of rock strength and degree of weathering. Obtained in combination with V p, shear or secondary (S) elastic wave velocity, V S, is used when calculating the Young and Poisson dynamic elastic moduli.

Modification of microstructural properties of rock caused by salt weathering, combined with the presence of crystallised salts and water, strongly affects the rocks elastic wave velocities. (Benavente et al., 2018). The determination of P-velocities in weathered stone samples could present difficulties due to waveform attenuation, which results in output signals showing a low signal-to-noise ratio (SNR). On the other hand, the generation and acquisition of pure S-waves in rocks is difficult (Wang et al., 2009). The most critical problems come from the contamination of S-waveforms by P-waves (P- wave appears before the S- wave arrivals), the reduction of waveform amplitude (lower SNR) and increase of wavelength.

As a result, picking of onset time of the S-wave, for both fresh and weathered samples, and the P-wave in highly weathered samples, becomes a complicated process. All of these difficulties limit the use of S-waves, particularly when calculating the dynamic elastic moduli, which considers a tabulated value of the Poisson’s ratio, yielding dubious estimations of elastic rock properties. Manual picking is a tedious and time-consuming process, which is subject to human error. Furthermore, manual operation relies on the attention of a trained technician, which can be a disadvantage when analysis of large volumes of data is required.