Salt Susceptibility Index for various building stones and their practical durability

The present study investigated the relationship between the Salt Weathering Index (SSI) (Yu & Oguchi, 2010) and WAC, which is one of the methods used to evaluate the physical properties of stone, using various salt weathering experiments on building stones and artificial stones. The stone types studied were tuff (Oya stone, Towada stone, Ashino stone, Nikka stone, Tatsuyama stone), granite (Makabe stone), sandstone (Tago stone, Indian sandstone), porous rhyolite (Koga stone), and brick. Of these, 10 types of bricks, both homemade and commercial, were used. As a result, there was a rough correlation between SSI and WAC, and the multiple linear approximation had the highest coefficient of determination. The reason for the variation in the approximation formula is the difference in rock structure. In other words, for porous rhyolite and some bricks, which were probably fired at high temperatures, the WAC value was higher than the SSI value, whereas, for sandstone and dense tuff which were formed at low temperatures, the WAC value tended to be lower. In addition, the highest coefficient of determination between the rate of dry weight loss (DWL) and the SSI was obtained in the salt weathering experiment using a total immersion method with Na₂SO₄, MgSO₄, and Na₂CO₃ solutions. This is probably because the MgSO₄ solution has the highest viscosity and crystallization occurs in the deeper layers, which flake off on re-immersion. For Na₂SO₄, the coefficient of determination is high, except for the Tago sandstone. Although the reason for this is unclear, it is considered that the Na₂SO₄ precipitated dissolved before it had time to grow sufficiently. In the case of Na₂CO₃, the DWL is high in the Indian sandstone, but this is thought to be because the quartz that makes up the sandstone dissolved in the alkaline solution.