Material characterization of the brick in the Ming Dynasty heritage wall of Pianguan County: A case study

Abstract

In this study, brick samples were collected from a heritage architecture, Ming Dynasty Wall of Pianguan County. The heritage wall presented macro- and micro- cracks, weathering, discoloring, surface scaling and salt crystallization. A throughout characterization was conducted on the wall brick samples at different heights and depths using polarizing microscope, scanning electron microscope, X-ray diffraction analysis, X-ray fluorescence analysis, TG thermogravimetric analysis, soluble salt and ion chromatography analysis and moisture content analysis. The microscopic observations showed that the surface brick powder exhibited more micro-pores, relative loose flaky micro-structure and macroscopic scaling and cracks. The mineral compositions and soluble salt analysis revealed that the wall bricks at bottom surface contained a large amount of sulfates, which may from rainfall, air pollutants, saline soils and groundwater. The sulfate crystallization led to many pores and cracks in the microstructure, eventually resulting in the cracking, surface scaling and loss of mass and strength that would potentially lead to structural damage of heritage wall.