Preliminary Outdoor Exposure Experiment
In order to determine the effect of the switching frequency of the extension/compression position on the degree of degradation, a preliminary natural outdoor weathering experiment was carried out with two sealants being exposed for 12 months. Sealant specimens according to Figs. 1 and 2 were prepared and cured for one week at 23°C and 55 % relative humidity (r. h.), followed by one-week storage at 50°C without humidity control. Afterward, one specimen of each sealant was installed on an outdoor exposure rack located in Yamanashi Prefecture in Japan facing south at an inclination angle of 45°. The sealant specimens were exposed to cyclic movements using three different switching frequencies (once/month, once/week, and twice/week), and, as a reference, no movement at all (fixed position without switching) as shown in Table 4. The switching of the compression and the extension positions was accomplished manually with the help of pliers and suitable spacers. The sealed joints were exposed to 0 %, ±15 %, and ±30 % movement.
Test results are shown in Fig. 3. As can be seen, exposing the specimens to movement had a strong effect on the degree of degradation (DoD) when compared to static exposure (no movement). However, no significant difference was observed between the specimens exposed to movements with different switching frequencies. With this result, we chose the switching frequency of the compression/expansion positions in the outdoor test procedure as once/month, giving consideration to work efficiency.