Applicability of Non-Destructive Methods for Assessing the Strength of Masonry of Existing Structures

Introduction. The compressive strength of masonry is the most important mechanical characteristic assessed during inspections of buildings and is determined based on direct testing of bricks and mortar selected from the walls. However, current regulatory documents also recommend the use of non-destructive testing methods, particularly while examining cultural heritage buildings. However, non-destructive methods fail to take into account differences in the strength of bricks and mortar joints in the surface layers and their main volume, interaction of bricks and mortar, as well as anisotropy of the mechanical characteristics of masonry. The article presents the results of a study of the anisotropy of the compressive strength of ceramic bricks and an analysis of its influence on the results of assessing the strength of masonry using indirect methods.

Materials and Methods. The object of the research are two types of bricks: historical bricks from the walls of the barracks of the Brest Fortress built in 1933, as well as modern bricks produced in the Republic of Belarus. The strength of the brick was identified under a compressive load in the direction of the front, support and end surfaces on cubes with an edge size equal to the height of the brick.

Research Results. Graphs of the ratio between the obtained strength values of experimental cube samples under compression perpendicular to the front and end surfaces of the brick to the compressive strength perpendicular to its supporting surface are presented. Similar studies by other authors, including on ceramic cylinder samples, are analyzed. It was found that the compressive strength of the historical bricks perpendicular to its front and end surfaces was higher than their compressive strength perpendicular to the supporting surface. The opposite pattern was observed for modern bricks. However, due to the high variation of the results, it is not possible to establish a correlation between the compressive strength and the direction of the compressive force.

Discussion and Conclusion. The results of some studies that have shown that ceramic bricks are an anisotropic material are presented. A possibility of using non-destructive testing methods for brick strength has been evaluated, as well as that of designing a calibration ratio linking the compressive strength of a brick with the results of indirect testing of the front surface. 

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