successful measurements in the laboratory, the system was tested on the columns (Ø = 550 mm) of the Marmorpalais in Potsdam (see Figure 2). These are heavily weathered and show cracks, some of which have been filled.
Figure 5 shows the found structure of the marble. Although signals could be received at this object, they had large interference components. An automatic detection of the signal beginnings and thus an evaluation of tomography was not possible. The performance limit of the system was reached because of the strong fissuring of the stone.
Figure 5: typical structure of the marble columns of the Marmorpalais in Potsdam.
Discussion
The measurements on the ultrasound phantoms prove the principle functionality of the new ultrasound system in the creation of tomography on stone. The positioning of the ultrasonic transducers with the holding system takes approx. 30 min. and the recording of the positions approx. 10 min. The actual measurements and the calculation of the tomography take approx. 20 min. with max. 32 transducers. The determination of a tomography is thus easily possible within one hour. The transmission voltage of 1,000 Vpp at 9 mm aperture of the transducers is not sufficient to receive evaluable signals in case of strongly weathered and fissured marble. In addition in all cases, the high transmit voltage on the multiplexer generates a coupling to the receive channels. The resulting signals allows a reliable measurement only from 150 mm marble thickness.
Conclusion
The principle feasibility and the associated time saving could be demonstrated. However, a device that can be used practically requires the revision of the multiplexer and the electronics. As mentioned before, the high transmitt voltage generates a coupling to the receive channels and therefore the begin of the signal is difficult to define and structures thinner than 150 mm cannot be examined. This problem can be solved by a new layout which carefully separates the transmit and the receive parts of the electronic and their electrical grounding.
Furthermore, the holding system of the transducers 244should be optimized to allow a strong and secure mounting of the transducers on the marble surface. The existing system software has many useful features and is easyly to handle. Together with an optimized hardware, the system could accelerate the tomography of stone made cultural heritage.
Acknowledgements
The development was supplied by the Federal Ministry of Education and Research of Germany, VIP+00291.
References
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245
FUENTE DE CIBELES OF MADRID AND DECAY OF MONTESCLAROS MARBLE
David Martín Freire-Lista, Luís Sousa
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.
UTAD – Universidade de Trás-os-Montes e Alto Douro, Quinta de Prados, 5001-801 Vila Real, Portugal
CGeo – Centro de Geociências da Universidade de Coimbra, Rua Silvino Lima, Universidade de Coimbra, Polo II, 3030-790 Coimbra, Portugal
Abstract
Fuente de Cibeles of Madrid (Spain) was carved in Montesclaros marble between 1777 and 1782. In order to know its modifications and anthropogenic decay throughout its history, a documentary search was carried out. Montesclaros marble and its deterioration have been evaluated with optical microscopy, mercury intrusion porosimetry and colourimetry. In addition, the linear microcrack density from the surface to the interior of an altered sample was calculated. This dolomitic marble has coarse equigranular blasts and granoblastic texture. Dolomite crystals are surrounded by smaller calite crystals that dissolve more easily. This dissolution produces pores, a slight colour change and finally granular disintegration. Rhombohedral exfoliation microcracks are more numerous in the first superficial millimeters of altered stones.
Keywords: Fuente de Cibeles, marble decay, weathering processes, maintenance
Introduction
Traditional building
