Mortar Water Content Impact on Masonry Strength

Abstract

Building without sufficient knowledge can entail risk concerning structural safety and resource efficiency. The authors of this paper share the view that mortar water content are subject to large variations, and that the consequences of these variations are unknown or neglected. A literature review and a test program has therefore been conducted in order to investigate how the mortar water content influence the following important strength properties of masonry: Flexural strength, initial shear strength and compressive strength. Prior to the test program, the first-author visited six different buildings sites in order to document on-site mortar consistency. Based on this, three mortar mixes (dry, medium and wet) were chosen for the test program. The testing is conducted basted on NS-EN 1052 series [1-3], and comparison is made to values given in Norwegian Annex of Eurocode 6 [4].

It is found that there is a lack of knowledge on this issue in literature, and further that the guidelines for masons regarding mortar water content is insufficient. The test program showed that the structural properties vary considerably based on the water content of the mortar. Flexural and initial shear strength increases strongly by increasing the water content, seven-fold for shear. The compressive strength of masonry specimens show on the other hand consistent strength that seems independent of reduced mortar strength by increased water content. The recommendation of using wet mortar ought to be included in the curriculum of masons. Since the scale of the presented research is rather limited, further testing ought to be carried out.