Читать книгу Monument Future - Siegfried Siegesmund - Страница 135

Already at the first inspection it was noted that the individual sculptures are affected to a varying degree by delamination and disintegration.

As a first step, level and extent of both decay patterns were thus assessed visually and sensorily as well as recorded in descriptive form and visualized in mappings. It revealed that the two steles are mainly affected by delamination while the human- and animal-shaped sculptures suffer from disintegration. This already suggests a link and dependence between the stone variety and the main decay pattern. Further, the survey showed that particularly the upper third of each of the steles is affected by delamination.

On the main stele the east face shows a more extensive scaling parallel to the surface than the opposite. The human- and animal-shaped sculptures show an even roughness on all sides. Surfaces are hardly sanding, which is likely due to a past consolidation treatment as communicated by NCCH.

Figure 2: Detail of the delamination in the upper third of the main stele, 2018. © Amarsanaa.

In a second step, a set of non-destructive field tests were carried out in order to further characterize and evaluate the degree of decay and weathering. Multiple ultrasonic pulse velocity measurements using the PUNDIT^® PL-200 (Proceq) with p-wave transducers 250 kHz (and 350-fold receiver gain) were done at all objects in different directions to detect cracks, voids and cavities within the materials more precisely. Further, inhomogeneity or disintegrated areas, which are an indication of enhanced degradation, were determined. Figure 3 illustrates the obtained measuring results at the main stele. In the upper two thirds a signal was received only very sporadically. The measurements perpendicular to the layering (i. e. from east to west) showed an average pulse velocity of 1,769 m/s in the lower third. Parallel to the layering an average pulse velocity of 2,050 m/s was measured in the upper third.

At the small stele signal were received only sporadically perpendicular to the layering (i. e. from north to south) with an average pulse velocity of 949 m/s. Parallel to the layering an average pulse velocity of 3,116 m/s was measured whereby signals were detected over the whole height. At four of the animal- and human shaped sculptures (no. 2, 6, 7, 11) no signal was received regardless of the direction. At the others a transmission of the pulse was partly possible. Altogether the average pulse velocities were lower than those at the two steles. The Karsten tube and the contact-sponge were used to assess the Water Absorption Behaviour (WAB) of the stone materials in order to further describe the porosity and degree of weathering (Svahn 2006: 21; Vandevoorde et al. 2009; Vandevoorde et al. 2011). Of particular interest were striking deviations in the WAB among the individual objects.

The contact-sponge method was applied on all objects. Results revealed that the average water absorption (WA) of the stone varieties with layering is 0.76 g/ m²s (A1, main stele) and 0.59 g/ m²s (A3, small stele) respectively. Only a roughened surface 104on top of the west face of the main stele showed a maximum WA of 5.38 g/ m²s. The third stone variety (A2, human- and animal-shaped sculptures) shows a slightly higher average WA of 1.12 g/ m²s, whereby four sculptures (no. 6, 9, 11 and 14) stand out due to a noticeably higher WA.

Figure 3: Mappings of the ultrasonic pulse velocity at the main stele (no. 1); measurements at the front perpendicular to the layering (left) and at the side parallel to the layering (right).

Due to time constraints only the two steles and five human- and animal-shaped sculptures (No. 2, 4, 7, 9, 11) could be exemplarily tested with the Karsten tube method. Results obtained from this field test widely correspond to the results of the contact-sponge tests: the two steles showed very low to no WA over a period of 45 minutes. Among the animal- and human-shaped sculptures no. 9 and 11 had the highest WA, equivalent to the results given by the contact-sponge tests. The others showed a constant but slower water uptake.