Conclusions

The conclusions from this study are as follows:

(1) Two-sided adhesion joints used for sealing deep ALC panels were more reliable than that of three-sided adhesion joints used for the thin ALC panel type from the viewpoint of durability and degradation of the sealed joint of ALC panels in actual buildings. The damage to three­sided adhesion joints used in thin ALC panels was confirmed from partial damage located at 4 locations of 62. The hardness of the acrylic sealant was approximately 60 Shore A for sealants used in the joints of a 17 year old building. As a result of the tension tests, the maximum tensile stress achieved was 0.36-0.73 N/mm2 (mean value: 0.54 N/

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mm2). The maximum elongation at the fracture of the sealed joint was 53-223 % (mean value 117 %). Most fractures of sealed joint were thin layer cohesion failures where the sealant was fractured at the interface with the ALC substrate. In 47 of 62 specimens, cracks in the coating on the surface of the sealant were observed; however, these cracks did not penetrate into the depth of the sealant.

(2) In regard to the results on the surface condition of a sealed joint after 5 years of outdoor exposure, the aging (degree of dirt pickup) and the extent of the occurrence of cracks depended on the environmental con­ditions apparent at any exposure location. In particular, the exposure site with the highest average monthly temperature (climate zone) had, in this study, the greatest effect on the durability of the sealed joint. The longer the exposure period of the sealed joint, the lower the dura­bility of the sealed joint in respect to values obtained for the tensile stress and elongation. The degree of elongation of three-sided adhesion joints after 5 years of exposure was markedly decreased and its maxi­mum elongation was less than 50 %. A number of sealed joints after 5 years of exposure testing had failure at the ALC substrate (symbol: x).

Therefore, given that the maximum elongation observed for the acrylic seal­ant was less than 50 % and that the degree of movement accommodation of three-sided adhesion joints in ALC panels with such types of sealant is reduced, thereby increasing the likelihood of premature joint failure, it was determined that a suitable sealant for use on ALC substrates is a sealant having a greater degree of movement accommodation than acrylic sealants and also a product that has enhanced durability. Furthermore, in order to enhance the longevity of the sealed joints, it is recommended that for joints of ALC panel systems, the sealant products should be applied, as is usually the practice for other joints, as a two-sided joint.

Acknowledgments

This work was performed as part of the activities of the working group for the “Research of Sealants for Sealed ALC Panel Joints," conducted by the Tokyo Institute of Technology, Autoclave Lightweight aerated Concrete panels and the Japan Sealant Industry Association. This work was also supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology, Korea (Grant No. 2010-0011927). Some researchers were funded by the Korean Gov­ernment and supported by the 2nd Korea Brain (BK21) foundation. The writers are grateful to all these parties for their support.