Читать книгу Monument Future - Siegfried Siegesmund - Страница 159

In a first step of the strengthening of the west iwan the masonry was grouted with a gypsum suspension developed by University of Technology Dresden (TUD) and Jäger Consulting Engineers Ltd. The worm pump SP-20 from Desoi was absolutely necessary for the grouting of large caverns, cavities and crack systems in the north wall of the west iwan. The water-to-gypsum ratio of the aggregate-free suspension was 0.63. The chemical Retardan 200 P by SIKA Company was added as a retarder. Tests with ViscoCrete by SIKA Company showed that the addition of a plasticizer to the suspension was not necessary to guarantee sufficient flowability. The gypsum suspension could easily be mixed and processed on-site. Observation of the injection process confirmed the very good flow behaviour of the suspension which ensured the closing of the cracks and cavities in the masonry. The grout remained flowable long enough and the quantity of the water taken from the surroundings were within limits. The masonry showed heavy vertical cracks and numerous holes and cavities in the interior, which had to be grouted from the bottom to the top of the wall with the developed gypsum suspension. First holes were drilled at a spacing of 30 to 50 cm along the course of the crack to grout the masonry. The holes had a diameter of 24 mm and depths of 30 to 80 cm. After completion of drilling, the entire masonry including the cracks was prepared for the subsequent rising grouting. For this purpose the cracks were cleaned of dust and loose objects and the parts of the masonry facade near the masonry facade were secured with loam mortar. This prevented contamination of the masonry during the grouting work and the preceding filling of the cracks. Then grouting was started from bottom to top (Figure 7).

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Figure 7: Gypsum mortar injection into the cracked north wall of the west iwan. Right side: Bottom to top injection in sealed crack.

It was frequently the case that the masonry could be grouted up to 1 m of height from one hole. This demonstrated an effective internal transport of material, with continuous grouting of the entire masonry being guaranteed. At each level, grout escaped at the various holes drilled round the buttress. In total, 7 tons of gypsum suspension were grouted to the east part of the north wall of the west iwan.