[M-IS07] Geomaterials in cultural heritage: weathering, investigation techniques, and conservation

[MIS07-P03] Artificial stone construction and its heritage structures in Tokai area, central Japan

★Invited Papers

*Yukiyasu Fujii¹, Takehiro Amano², Kantetsu Asano³ (1.Meijo University, 2.Institute of Regional Research of Chubu, Aichi University, 3.Graduate School of Science and Technology, Meijo University)

Keywords:Decomposed granite soil, Calcium hydroxide, Compaction, Building stone

Artificial stone construction is traditional method developed by civil engineer, HATTORI Choshichi, who was born and grown in Hekinan city, Tokai area, central Japan. He had tried to develop the Japanese traditional method “Tataki” with the combination of building stones. Tataki is a kind of mixed soil in which decomposed granite soil, calcium hydroxide, and water are mixed, and they are well mixed and compacted with special instruments. The combination of Tataki and building stones, he had finally made the artificial stone construction, called as “Choshichi Tataki”. There are some artificial stone constructions which were build more than 100 years ago and have been well conserved and preserved especially in Tokai area. Some of them are designated as cultural properties. Shiofukibouhatei is a breakwater structure, located in Yokkaichi city and designated as a national important cultural property and a heritage of industrial modernization (photo). In addition, similar method had been applied to the conservation work for Bayon of Angkor Thom in Kingdom of Cambodia. After Portland cement had been produced domestically about 100 years ago, cost of artificial stone construction had been increased compared to concrete construction. Therefore, artificial stone construction had been fallen into rapid decline. However, the structures deteriorate gradually and conservation or repair work will be needed in near future.
There is no enough documentation for the method of artificial stone construction. It seems that engineer instructed orally the methos in Hattori-gumi, construction company produced by Chosichi. There are two important elements for the method of artificial stone construction. One is the appropriate ratio of decomposed granite soil, calcium hydroxide, and water to make “Tataki”. Another is how to build the structure, in which each building stones doesn’t contact with each other, and “Tataki” is filled with between the stones (photo). In this study, it is tried to find the appropriate ratio for “Tataki”.
Decomposed granite soil is made from the combination of Mikawa quartz sand and pyrophyllite clay. Artificial decomposed granite soil has controlled grain size distribution. The mixing ratio of decomposed granite soil to calcium hydroxide is 8:1, 10:1, and 15:1. This ratio was refer to the old documentation written by Aichi Prefecture. Water content ratio is 10 %, 15 %, 20 %. The optimum water content of artificial soil is about 10 %, so it's the minimum water content. The strength of “Tataki” might be increased with curing time of chemical reaction with water, as same as the concrete. Artificial soil is compacted in the iron-mold with three layers. Cylindrical specimens are made, the diameter is 50 mm and length is 100 mm. Uni-axial compression tests are applied to the specimens after the curing time of 14, 28, and 56 days. Increasing of the strength could be confirmed for all ratios of specimens. In addition, about the content ratio of calcium hydroxide and water, it’s more significant increase in strength with the higher of their content with curing time. The value of the strength is not so much as real “Tataki”. However, this results might contribute to the future study for the conservation and repair of the “Tataki ” for Artificial stone construction.