The Weathering Characteristics Of Stone Cultural Relics In Helan Mountains By Experiments

The rock paintings exposed for a long time in the natural environment will disappear because of serious weathering now.The rocks as carrier material of rock paintings as the research objects,which were collected by six partitions named by A,B,C,D,E and F.Fistly,the characteristics of rocks quality,natural water absorption and saturated water absorption were studied with immersion time after the investigation on current weathering status and water resource to establish numerical fitting of rocks water absorption function and reveal the change rules of water absorption characteristics in the time series.Then,the xenon test,freeze-thaw test and tunnel wind test were done to analyze the influences of light radiation,temperature and wind speed on the rocks quality and water absorption.The 240h,480h and 50h were the aging period respectively,and three cycle simulation experiments were carried out.At the last,slices with size of 1cm×1cm×0.1cm were selected to explore the pore characteristics and the cement structure by SEM microscopic with four different magnifications,and the features were compared with fresh rock samples,weathering rock samples and samples of different areas.The results showed that the rocks quality,natural water absorption and saturated water absorption increased with immersion time,and the relationship between the natural water absorption and saturated water absorption of rocks with the immersion time were logarithmic,and the weathering was more serious,the greater water absorption was.After the aging periods the quality decreased,but water absorption increased.Tthe weathering was more serious,the greater water absorption was,and samples from A and B areas were influenced greatly by these disease factors of light radiation,temperature,wind speed,also the water absorption rate of change was the most obvious,the degree of weathering was the most serious followed by E and F areas and C and D areas.The results of SEM showed that the weathering degree of rock paintings has a closely connection with its water absorption properties and microscopic characteristics.That is to say larger bibulous rate,more pore,more loose,more incomplete the samples structure,and more bigger the weathering degree.And at the same area,the structural integrity of rock samples with a fresh surface was strong,the local of samples was sheet or block and cementation was better,but the cracks of rock samples with a weathering surface was obviously.The holes were big and structure was loose.On the other hand,at the different area,more loose the microscopic structure was,more greater the porosity,more obvious the pore,more uneven the granular space of particles,more serious the rock damage and more greater the degree of rock weathering.So the water absorption and microscopic features can describe the degree of rock weathering,which will provide a scientific theoretical basis for the protection and restoration of Helan mountain rock paintings in the future.