D was used on dry and wet samples and at the onsite investiagtions.
Onsite investigations included damage mapping, surface hardness measurements, Karsten tube tests to detect the water uptake capacity, electrical capacity and conductivity. The investigations were done on the east façade of the Kathoghike Church (errected in 1215) and at the eastern wall of the Jamatoun of the Proshian (constructed in 1283). The latter consists of the rock cut structure (Fig. 1d, 3a).
Experimental conservation
Experimental conservation was done on the clast-free stone material of the rock by using a swelling inhibitor (Anti-Hygro, Remmers company) and consolidation with a silica sol and a silica acid ester (KSE 300, Remmers company). The samples were placed under conditions of complete immersion in the swelling inhibitor for one hour and dried afterwards. The same procedure was done in the case for consolidation. For consolidation the silica sol was diluted 1 : 1 with distilled water.
Results
Materials of construction and rock cut architecture
The basalt rock used for the construction of the architecture outside the rockface also shows 259varieties of different quality (Fig. 2a and 2b). It is noteworthy, that the foundation of the church building consists of a much harder basalt variety (BF) than the rising masonry (BW). The BF variety shows a macroporosity characterised by a distinctive lamination (Fig. 2a), while the basalt ashlars of the walls (BW) show a finely homogeneous porous structure (Fig. 2b).
The rock cut architecture is carved into the soft rock that can be divided into different varieties. A clear distinguishing feature is the clastic material. The sample material in this study distinguishes between a rock variety that is largely free of clasts (RF) and another that contains a high proportion of clasts (RC) shown in figure 2c and 2d. This clastic material may constitute up to 40 % of the rock and can display a diameter up to about 5 cm (Fig. 2c). The fine matrix has an ocher tone and shows a variety of brownish traces of oxidation (Fig. 1a, 1c, 2c and 3d).
It can be characterised as an ash-rich, welded tuff with a fine matrix containing a large percentage of microlites, more or less uniform in size from idiomorphic feldspar crystals (Fig. 2e and 2f). Some of these can be identified as plagioclase.
In this study two types of this tuff rock were investigated further: the clast-rich (RC) and a clast free material (RF), (Fig. 2c–2f).
Figure 2: Different building materials used for the monastery. a) The basalt of the foundation (BF) and b) the basalt of the walls (BW). c) The rock variety with clasts (RC) and d) the variety without clasts (RF). e) Thin section of RC and f) of RF under polarised light. The pore size distribution of RC (left) and RF variety (right) is shown below.
Onsite investigations
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).
Laboratory investigations
The porosity of the basaltic building stones range between 17.4–23.5 % (Tab. 1). The rock material shows a very high porosity of 30 % (RC) to even 38.2 % for the RF variety (Tab. 1). The fine variety (RF) contains a microporosity (0.001–0.1 µm) of 10.2 %, whereas the RC variety contains 23.2 % microporosity (Fig. 2 below).
The saturation degree S of all investigated samples is high. The S-value of the RF variety is 0.94 and for the RC variety 0.97. The two basalt varieties show similar values: 0.97 for the basalt sample of the foundation and 0.95 for the sample from the wall.
Directional water uptake of the rock material, however, shows different values. Z means perpendicular to the bedding, X parallel to the bedding and Y parallel to the bedding and parallel to the lamination of the stone material. Water uptake for the clastic rock (RC) sample attains a value of around 11.8 kg/m2/√h in all directions. Much lower values 261were determined for the fine-grained variety (RF), which show values of 4.6 and 4.5 kg/m2/√h for the XY direction and 5.2 kg/m2/√h for the Z direction, thus attaining an anisotropy (A) of 13 %. This tendency could also be shown by the measurements of ultrasonic velocity, expecially in the case of the fine-grained rock variety (RF), (Tab. 2).
Table 1: Porosity and density of the investigated stone samples.
| Sample | Porosity (%) | Density (g/cm3) |
Matrix-density (g/cm3)
|
