Investigations Of Weathering Processing Of Sandstone Monuments By Materials Characterization Techniques

Cultural heritages behave as the carrier of history and cultrue of human and are a bridge that connects the ancient and present culture and civilization. Witnessing the development of human history, they are non-renewable as well. However, under the combined influence of the natural and human factors, a great number of important outdoor immovable stone monuments, including the Yungang Grottoes, are suffering from severe weathering damage, which is obviously irreversible. Immediate actions are mandatory to prevent or delay them from further weathering, although it is considered as a looming and arduous task.In the present dessertation, a variety of materials characterization techniques, such as X-ray diffraction, x fluorescence spectroscopy, scanning electron microscopy with EDX, portable X-ray detector, ion chromatography, Minispec TD-NMR apparatus etc, were applied to analyze the composition of the fresh rocks and the natural weathering reminders collected from Yungang Grottoes, Which showed that sulfate was the main reason of chemical weathering. Then, the composition and structure changes of sandstones under the effect of the SO2, CO2 and other acid gases combined with water were explored. Our results showed that the combination of acidic gas and water made up of feldspars decompose into stable kaolinite while the soluble salts formed during the aging experiment lost water that exacerbated the weathering preocessing of stone.Secondly, the fresh sandstones collected from Yungang and DaZu regions were aged in W-WD and 20% G-WD at constant temperature in our laboratory to obtain samples with different aging time. These samples were characterized in detail and results are summarized as the followings:(1) Portable X-ray detector can explore defects inside sandstones, such as cracks, cavity, and so on, but some useful information of micro-cracks may be ignored by this technique, indicating it is necessary to further improve its ability in detecting the microcracks inside the stone;(2) Testing of the vertical rock relaxation time T2 of H atoms, T2 and the aperture size by NMR corresponds to certain linear relationship, indicating that the pore size distribution within the rock as well as the ratio can be reflected directly with accuracy in a rang of micron. Therefore, it can be used to deduce the distribution of internal pore size in sandstones with different weathering degree. The pore size can be used as a quantitative indicator of weathering degree;(3) The precipitate concentration of various cations were increaseing with the degree of aging deepened. Na+ shows the largest precipitate loss and the fastest dissolution rate in the water. In contrast, the change of Mg2+ is relatively stable. The study of ion concentration in precipitations shows that the temperature is the most factor that results in the ions loss in the stones.(4) During the aging process, in a certain range, the water and saturation water absorption increase with the weathering, the growth trend shows nearly linear relationship. Therefore, water absorption and saturation water absorption of sandstone could be set as the quantitative evaluation indicators of weathering degree.According to the analysis of test results, the aging test is feasible.