Читать книгу Monument Future - Siegfried Siegesmund - Страница 412

Hydrostatic weighing on drilling cores was carried out to acquire the particle and bulk density as well 265as the porosity (DIN 52102). Hydric dilatation was measured on drill core samples taken perpenticular to the bedding using a dial gauge under conditions of complete immersion in demineralized water.

The structural properties of the areas near the surface as well as the material cohesion of the tombstones were examined using two different methods: micro-hardness and ultrasonic velocity. Both measurements were carried out before the consolidation and after.

An Equotip 3 device (proceq) was used for the surface hardness measurements. A rebound hardness impact device with hardness level D was used.

For the measurements of the ultrasonic velocity, the tombstones were measured with a 52 kHz compression wave transducer. The pundipLab+ (procec) was used as the pulse generator. The measurements on the sandstone tombstones were carried out in a grid by transmission.

To determine the causes of the observed deterioration, the electrical conductivity of the tombstone was investigated using two different methods.

The electrical conductivity was measured using a portable measuring device (Protimeter Surveymaster, General Electric). This technique allows conclusions to be drawn about hygroscopic salts and moisture.

In addition, the electrical conductivity was measured using a cotton test pad moistened with distilled water (Fig. 3a). This measurement method can also help to detect non-hygroscopic and less soluble salts like gypsum.

The three sandstone tombstones were desalinated using a combined process of directional moisture flow and compresses (Domaslowski 2003, Wedekind 2016a). For this purpose, a permanently moist compress was applied to the west side of the tombstone, which was moistened with distilled water over a period of about three months by a system of drip devices (Fig. 2a). Around 50 l of destillated water was used for each tombstone during the desalination process. Drying could only take place on the damaged east sides of the tombstone, on which a poultice was also placed. The rest of the tombstone body was covered with a plastic film (Fig. 2a).

The poultices were made from fine washed sand and cellolose in a volume fraction of 4 : 1 mixed with destillated water. After total drying the poultices were sampled gridwise and each sample diluted with a controlled amount of destillated water with respect to each sampling area, mixed and measured by electrical conductivity. The dried poultice has a porosity of 57 % (about twice as much as the sandstone of the tombstone) and a pore size distribution ranging in the size classes of 1 to 20 µm as measured by mercury intrusion porosimetry.

After salt reduction the damaged areas of the three sandstone tombstones were consolidated with a silica acid esther (KSE 300, Remmers company) (Fig. 3b).