[H-TT15] Non-destructive techniques applied to stone cultural heritage

[HTT15-02] Measurement of anisotropy of liquid water diffusivity of brittle tuff stone of Takase stone buddhas using X-ray

*安福 勝¹、平沼 柊哉²、麓 隆行¹、脇谷 草一郎³、小椋 大輔⁴ (1.近畿大学、2.積水ハウス株式会社、3.独立行政法人国立文化財機構　奈良文化財研究所、4.京都大学)

キーワード：石仏、ボルツマン変換、材料物性

Takase Stone Buddhas is one of the important old stone buddha sculptures curved into the inner wall of the caves in Oita, Japan. It is located in a cave curved into the cliff of a hill of volcanic tuff. In general, because the cave is currently protected from rain and direct solar radiation by the roof shelter and waterproof treatment, the Buddhas is well conserved and no currently ongoing weathering can be clearly observed. However, because of a high ground water level, there is a concern in the influence of water evaporation at and near the surface of the stone buddhas and the wall of the cave on their deterioration. In the past, we have been conducting our long-term field survey of the conservation environment and numerical analyses of heat and moisture transport in the cliff and stone buddhas. The field survey provided a yearly data set of the conservation environment that was used as input of the succesive numerical simulation of heat and water transport in the material, which strongly depends on the material properties of the tuff stone.

In this study, we have conducted a holistic study of the material properties of the tuff stone of Takase stone buddhas, with special attention to the anisotropy of liquid water diffusivity. Because the tuff stone of the Takase stone buddhas is rather brittle, X-ray was applied to enable non-destructive measurement of the anisotropy of the diffusivity so that the specimen neither deforms nor collapse. X-ray CT was used to understand the three dimensional characteristics of a specimen. The liquid water diffusivity of the specimen was measured for different directions using X-ray radiography. The results showed a strong anisotropy of the liquid water diffusivity. The measured data were taken into account the succesive numerical study to quantify the importance of the anisotropy of the liquid water diffusivity for the conservation of the stone buddhas.