Читать книгу Monument Future - Siegfried Siegesmund - Страница 397

The results of the mapping of the eastern façade of the church building show that back-weathering, concentrated at the upper part of the façade is the main damage form reaching more than 5 square meters of ashlar (Fig. 3c and e). This can be partly associated with effloressences of salts. Using test stripes the high amount of sulfate (> 1,600 mg/l) and nitrate (500 mg/l) could be detected. The high values of sulfate may be due to the use of cement mortar, implemeted during restoration works on the roof. Moreover, rain water caused immense infiltration, which is noticable by the crust formation on the outer masonry shell (Fig. 1b). The basalt ashlar of the masonry (BW) shows a clear water absorbtion by Karsten tube, probably due to its remarkable porosity of 23.5 %. Its surface hardness with around 300 HLD is comparably low. The basalt ashlar of the foundation does not show any water uptake by Karsten tube tests. With around 700 HLD under dry conditions and 624 HLD under wet conditions a more than twice as high surface hardness than the ashlar of the walls could be measured for the BF variety. Cracks were only found in the lower part of the façade, probably due to seismic activities in the past (Fig. 3c).

In contrast to the basaltic ashlar (BF and BW), the natural rock material shows low values of surface hardness ranging between 275 and 300 HLD under dry and 261 HLD under wet conditions. A small 260reduction of 5 % at the lowest point. The clastic material (RC) also shows various values ranging from 130 to 450 HLD under dry conditions also depending on the rock clasts. The clasts show values between 250 and 450 HLD. The matrix reaches an average value of around 250 HLD under dry and 227 HLD under wet conditions, which is a reduction of 9 %. Sanding and back-weathering of the matrix is the main weathering form observed on the rock cut architecture (Figure 3d).

Figure 3: a) The floor plan of the monastery. Areas of investigation indicated. b) Architectonic drawing of the investigated church façade. c) Damage mapping. d) Crack formation or scaling of the rock material. d) Typical back-weathering of a porous basalt ashlar.

In some parts of the upper wall active water infiltration takes place. Electrical conductivity and capacity reaches critical values at various parts of the inner walls of the rock cut structure. The exposed rock also shows crust formation and cracks (Figure 3d). These cracks are partly closed by a restoration mortar to prevent water infiltration.

Water uptake by Karsten test pipes show high values for the rock. This also corresponds to the high porosity of the rock material investigated in the laboratory (Table 1).