关键词: 壁画地仗, 盐害, 可溶盐, 毛细输送机制, 敦煌石窟

Abstract: In this study a device has been developed to simulate the capillary water and salt migration. The pore solution migration in the desalinated and pure Dengban soils can be monitored under the temperature-, humidity- and water head-controlled conditions. Before and after the capillary test, thermal conductivity and pore radius of the specimens are determined to estimate the contribution of external and internal salts to the salt damage of mural from the microscopic viewpoint. The experimental results show that solution migration rate decreases in the order of mixed KCl and Na2SO4 solution ? KCl solution ? Na2SO4 solution ? distilled water. The capillary rise rate decreases gradually with the specimen height, and the capillary rise rate in desalination Dengban soils is greater than the pure Dengban soils. The electric conductivity of soil solution increases vertically with the soil specimen height, and the conductivity of pure Dengban soil is greater than that of desalinated Dengban soil. The thermal conductivity of the soil specimens shows an overall tendency that increase first and then decrease with the rising specimen height. Compared with the pure Dengban soil, the pore-size distribution density of the desalinated Dengban soil reduces to a small aperture. In the case that the mixed salt solution is transported in soils, and pore sizes are concentrated in a more narrow area than that if single salt solution is used. It is shown that the salts transported by capillary, especially mixed sulfate and chloride, induce more severe damage than the salts contained in the soil, indicating that it is important to prevent rain water from leaching into upper caves for mural conservation.

Key words: mural plaster, salt damage, soluble salt, the mechanism of capillary conveying, Dunhuang Grottes