ESTIMATING THE WEATHERING DEGREE OF ROCK SURFACE OF CULTURAL RELIC FROM LEEB HARDNESS FOR NON-DESTRUCTIVE MEASUREMENT

Equotip(Leeb hardness tester) is invented by Dietmai Leeb in the 1970s. At first, it was designed for detecting the hardness of metal materials. For it has the characteristics of small impact energy, undemanding impact direction, more sensitive to rock strength changes, it can be applied to non-destructive measurement of rocks. The authors used it to measure flake weathered rock surface of Yungang Grottoes, Datong, Shanxi province. The average hardness values of three chosen measurement regions were 224.8, 225.8 and 236.4,respectively. However, the average Leeb hardness value of unweathered rock with the same lithology was 661.4. According to the above measured values, the authors define the weathering degree, that is the ratio of the hardness values of weathered rock to that of fresh rock. Accordingly, the weathering degrees of the three measurement regions were 0.34, 0.34 and 0.36 respectively. According to the formula of Leeb hardness value and uniaxial compressive strength summarized in the literature, it also obtained that the uniaxial compressive strength of the three measurement regions were 6.06MPa, 6.13MPa and 6.87MPa, respectively.