Study on weathering corrosion characteristics of red sandstone of ancient buildings under the perspective of non-destructive testing

Abstract

As one of the main building materials of ancient buildings, the unique weathering characteristics of red sandstone pose a serious challenge to the stability and protection of building structures. In order to quickly and accurately explore the weathering and erosion characteristics of the red sandstone structure of an existing ancient building, we used scanning electron microscopy (SEM) and X-ray diffraction (XRD) to explore the microstructure and material distribution of different parts of the red sandstone of ancient buildings, and used X-ray computed tomography (X-CT) images to obtain quantitative damage information of the structural layering of the red sandstone, and corresponded it to the ultrasonic velocity characteristics at specific locations. In order to reduce the noise of the original X-CT images of ancient buildings red sandstone and enhance the image contrast to obtain accurate quantitative information, we using the histogram peak signal-to-noise ratio (PSNR) as the effect parameter for the X-CT original image noise reduction and enhancement process, and finally preferred the best processing methods, to differentiate the weathering damage characteristics of the cross-section. Subsequently, the consistency of damage analysis between images and ultrasonic velocities from red sandstone structures was comparatively verified based on predictive modeling of small data samples. Finally, the model was used to predict the image and ultrasonic velocity damage characteristics of the red sandstone respectively, and the weights of the two sets of data were assigned by the CRITIC weighting method, so as to realize the comprehensive assessment of the weathering damage of the red sandstone by combining the image and ultrasonic velocity. The results show that: (1) During weathering, During weathering, the mineral components in red sandstone react with carbon dioxide, water and oxygen in the air to produce dolomite and chlorite. The generation of dolomite and chlorite can protect the red sandstone to a certain extent, preventing it from further corrosion by weathering and prolonging its stability and life. (2) The digitized image of the red sandstone has a damage degree of 22.62 %, which is close to the ultrasonic velocity based damage degree of 22.29 %. Both compared to the L1 comprehensive evaluation of the boundary surface damage of 20.65 %, and converted to the comparison of the bottom surface its damage reaches 22.93 %, which is close to the damage through the rebound strength of 23.94 %. This also verifies the accuracy of the results and methodology, based on the NDT perspective of the ancient architecture of the red sandstone weathering corrosion characteristics of the evaluation analysis can be better applied to engineering practice. (3) There is an obvious layering phenomenon after weathering and corrosion within the ancient buildings red sandstone structure, with a slow linear distribution below the L4 layer. The damage degree of the L5 layer and the top surface boundary is close to each other. Therefore, it is inferred that there is a weathering and corrosion performance sub-interface between the L4 and L5 layers, parts of the red sandstone above the sub-interface of the deterioration of the damage is serious.Based on the above results, we form a systematic and reliable nondestructive testing and damage quantification system for sandstone structures in ancient buildings, we can divide the structure into intact structure and weathering damage structure in the depth direction based on a certain structural damage threshold. In the process of restoration and replacement of ancient buildings, the construction location can be determined quickly and without damage, which will provide a reference basis for the restoration and preservation of ancient building structures and similar projects.