Читать книгу Monument Future - Siegfried Siegesmund - Страница 413

The porosity of the three tombstones varies between 22 and 24 % (Tab. 1). The hydric dilatation for the sample from tombstone I was 0.7 mm/m, for tombstone II 0.1 mm/m and for tombstone III 0.9 mm/m.

A significantly increased electrical conductivity could be measured in the areas with observable weathering (Fig. 4). The three tombstones show different forms and intensities of weathering. In the lower part of the eastside of tombstone I, a semi-circular weathering of the stone due to sanding has developed, whereas the opposite side (west) shows an alveolar-like pitting (Fig. 1a). On the lower part of tombstone II (eastside), a low alveolar weathering can be observed, the backside does not show any relevant deterioration (Figure 1b). Tombstone III shows intense flaking and sanding parallel to the layer over the entire engraved writing part, while the backside is nearly intact (Fig. 1c).

The values for the porosity of the three different tombstones are also comparable (Tab. 1). However, the electrical conductivity values of the west sides of all tombstones are very low (green).

Testing of salt reduction show different results for all tombstones. The highest electrical conductivity in the poulice samples could be measured in tombstone III followed by tombstone I and finally 266tombstone II (Fig. 5). The electrical conductivity of tombstone I ranges from 0.2 to 5.07 mS/cm, for tomstone II from 0.16 to 3.83 mS/cm and for tombstone III from 0.949 up to 12.0 mS/cm.

Figure 3: a) Electrical conductivity measuraments using test pads and b) consolidation with a squirt bottle.

Figure 4: Values of electrical conductivity for a) tombstone I, b) tombstone II and c) tombstone III. Values of electrical conductivity using test pads for d) tombstone I, e) tombstone II and f) tombstone III.

The ultrasonic velocity of the three sandstone tombstones show different values. At tombstone I, the ultrasonic velocity ranges between 2.011 km/s and 2.309 km/s and reaches an average value of 2.154 km/s. Areas with a comparatively weak cohesion could be detected in the middle area of the tombstone (Fig. 6a). After consolidation, an increase in the ultrasonic velocity could only be found in the lower, heavily weathered zone (Fig. 7a).

Tombstone II showed, overall, higher values. These lie between 1.994 km/s and 2.621 km/s and reach an average of 2.25 km/s (Fig. 6b). After consolidation, hardly any changes in the ultrasonic velocity could be detected (Fig. 7b).

Tombstone III showed the lowest ultrasonic velocity values. They range from 1.34 km/s to 2.234 km/s and are only around 1.94 km/s on average. The lowest values are concentrated in the middle and in the lower, middle area of the stone (Fig. 6c). Due to consolidation, cohesion was strengthened in almost all areas that were severely weathered. However, only a few areas reach values of 2 km/s.

Before consolidation, the surface hardness at tombstone I reached a maximum of 444 HLD and a minimum of 303 HLD. The average is 398 HLD. A slight softening can be seen in the upper center of the tombstone (Fig. 6d). After consolidation, the surface strength could only be slightly increased in some parts (Fig. 7d). However, the values reach around 400 HLD, which speaks for a certain strengthening affect.

Comparably higher values between 316 HLD and 499 HLD are achieved with tombstone II (Fig. 6e). On average, however, a slightly lower value of 392 HLD was measured as compared to tombstone I. This also corresponds to the observations and the overall measurements, which illustrate that in particular whose central area of the tombstone shows strong softening (Fig. 6e) The consolidation showed clear successes here.

Almost all areas with comparably low values could be adjusted to the surface strength of apparently intact areas (Fig. 7e). Some of these areas will return to values above 400 HLD after consolidation.

The most pronounced weathering and the lowest surface hardness values were observed and measured in tombstone III (Fig. 6d). They ranged from 487 HLD to just 272 HLD. Only an average of 319 HLD could be given. Due to the consolidation, the values were partially increased. However, 267they do not achieve a satisfactory result everywhere (Fig. 7d). Values of over 400 HLD could not be achieved in any of the measured areas after consolidation.

Table 1: Porosity and density of the investigated tombstones.

Sample	Porosity (%)	Density (g/cm3)	Matrix-density (g/cm3)
Tombstone I	24.0	2.01	2.64
Tombstone II	25.0	1.99	2.65
Tombstone III	22.4	2.02	2.61

Figure 5: Results of salt reduction testing using the single poultice samples for a) tombstone I, b) tomstone II and c) tombstone III.

Figure 6: Values of ultrasonic velocity for a) tombstone I, b) tombstone II and c) tombstone III and values of surface hardness for d) tombstone I, e) tombstone II and f) tombstone III before consolidation.

Figure 7: Values of ultrasonic velocity for a) tombstone I, b) tombstone II and c) tombstone III and values of surface hardness for d) tombstone I, e) tombstone II and f) tombstone III after conservation.

Restoration of the tombstones were done using a hot lime reaction mortar (Fig. 8). Similar mortars were already sucessfully prepared for tuffs and sandstones (Teipel et al. 2020, Wedekind et al. 2016b).