Читать книгу Monument Future - Siegfried Siegesmund - Страница 214

The hydric expansion was determined for all limestones on cylindrical samples (Ø 15 mm × 100 mm). The length change of those cylinders was measured under water-saturated conditions. The samples were completely immersed in demineralized water for 24 hours, meanwhile the expansion of the samples was measured with a displacement transducer. The resolution of the transducer is 0.1 µm and the accuracy is about 0.5 µm.

Figure 3: Evolution of the moisture expansion during a 24 hours test.

Figure 4: Bowing behavior of the selected limestones under wet and dry cycles.

Figure 5: Bowing effect after heating cycles.

To determine the bowing potential and its directional dependence, slabs of 40 × 10 × 3 cm were exposed to heating cycles (20–80–20 °C per day) simulating in an accelerated procedure the conditions at the building. Additionally, the specimens were 148exposed to thermohydric conditions, as the slabs were moistened on one side and cyclically heated on the reverse slab surface. The slabs were heated for 6 hours before they cool down to ambient temperature and the water was refilled 2 hours before the next heating cycle started. The bowing was measured by means of a measuring bridge with an accuracy of l µm/35 cm. A total of 91 cycles were performed (for details see Koch and Siegesmund 2002).

Figure 6: Progressive increase of residual strain for 20–90–20 °C cycles of the VAV samples. Investigated as a function of the number of heating cycles under dry (3 cycles, red background) and wet (4 cycles, blue background) conditions.

Thermal expansion measurements took place in the temperature range of 20–90 °C using a pushrod dilatometer (for details see Koch and Siegesmund 2004). The specimens had a length of 50 mm and a diameter of 15 mm. The residual strain (RS) was determined within seven heating–cooling cycles: 3 dry cycles 20–90–20 °C and 4 wet cycles 20–90–20 °C, in the Z and XY directions. RS is determined by the ratio between the sample length change after the heating–cooling cycles and the initial length (Shushakova et al. 2013).