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

[MIS07-P02] A study on the effect of rock properties on the application of hydrophobic treatment to prevent stone deterioration

*Mitsuru Takano¹, Chiaki T Oguchi² (1.Department of Engineering, Saitama University, 2.Institute for Environmental Science and Technology, Graduate School of Science and Engineering, Saitama University)

Keywords:tuff, granite, cement mortar, hydrophobic treatment, salt weathering experiment, sodium sulfate

Various measures have been taken to prevent damage to the stone, such as applying hydrophobic treatments to the stone surface to protect it from weathering, however, there is little work reporting on the effectiveness of those agents through weathering experiments. The present study carried out the porosimetry analysis and weathering experiments on stones treated with hydrophobic agents. The specimens used in the experiments were Tatsuyama stone (tuff), Ashino stone (welded tuff), Towada stone (tuff), Inada stone (granite), and cement mortar. The hydrophobic agent named Higo Guard manufactured by Higo-ya corporation was used in this experiment. We prepared two types of stone: one with a hydrophobic treatment to all surfaces except the base, and one without. The samples were placed on a Petri dish with beads and a saline solution of sodium sulfate and magnesium sulfate. The process of heating and cooling was repeated in a drying oven at 40°C and 5°C for up to 25 cycles. During the experiment, the salt solution was replenished every 48 hours. At the end of the experiment, the precipitated salt and detached stones were removed and the weight of the test piece was measured and compared with the weight before the experiment. In addition, P-waves and S-waves were measured at the center of the long axis of the sample using the Pandit lab+. The length of the area where salt had precipitated or a crack had formed from the bottom of the sample, i.e. the height of the capillary rise, was also measured. In the case of Inada stone and mortar, salt precipitation was observed in the uncoated samples, but no rock spalling was observed. However, the P-wave velocity decreased after the experiment. For Ashino stone, salt precipitation was observed in the lower 1 cm of the two samples coated with a protective agent, but no rock spalling was observed. On the two unprotected samples, spalling was observed over the entire surface and weathering had progressed. The P-wave velocity was also about 1000 m/s lower for the uncoated samples than for the coated samples. For the Tatsuyama stone, although some salt crystallization was observed on the surface of both preservative-coated samples after 13 cycles, no surface spalling was observed. However, peeling of the stone was observed on the underside of the samples at the end of the test. In addition, the samples coated with the preservative did not weather as much as the other samples. In the case of the Towada stone, the two samples treated with the agent had a relatively large area of salt precipitation after 13 cycles. After the test, three of the samples had collapsed, except for the one treated with the preservative and tested with sodium sulfate. From these observations, it can be concluded that the hydrophobic agent has caused damage to the Towada stone. The porosity of Towada stone is greater than that of Ashino stone and Tatsuyama stone, and it is possible that the hydrophobic agent penetrated too deeply into the stone, resulting in insufficient surface coating and preventing the agent from having any effect.