Influence of Workmanship on the Compressive Strength of Structural Masonry

Abstract

Structural masonry is a composite material that consists of brick/block units and mortar. Often, masonry is treated as a homogeneously material. The key mechanical characteristic of structural masonry is its compressive strength perpendicular to the bed joints. Estimating or even predicting this material property is thus an issue of central importance to assessing the reliability of masonry structures. As part of a course on structural masonry taught at ETH in Zurich, students are given an opportunity to do some practical work. During one lecture (one and half-hours) students are divided in smaller groups (five to six students) and each group is asked to build a standard masonry specimen (according to the European testing standard EN-1052-1) in the structural laboratory of the Institute of Structural Engineering. Simultaneously, two professional masons, which are instructing/helping students during the exercise, are asked to build one specimen. Such practical work has been performed every year since 2007, usually with clay block masonry, but also with calcium-silicate and AAC masonry. After the prescribed curing time all specimens are tested and the corresponding results (masonry compressive strength) are discussed with students. This paper presents the results and statistics of these test series. Special attention is paid to the influence of workmanship. Namely, strengths obtained from tests on specimens built by professional masons are, for all series, more or less near the mean values in spite of the fact that almost all students are without any skills as masons. The reasons for such distribution of the results are investigated and the findings are presented.