Assessing the effect of different mortar mixes on strength of burnt clay brick masonry wall

Abstract

Following the tremendous increase in population growth rate in Uganda from 12.6 million people in 1980 to 34.6 million people in 2014, there has been an increase in housing units from 2.6 million house in 1980 to 7.34 million houses in 2014. Despite of this increase in housing units, the population has surpassed the demand leading to a deficit of 200, 000 housing units annually. The National Housing and population census of 2014 revealed that the increased housing units is constructed of permanent materials at 43.7% with burnt clay bricks leading at 36.4% followed by mud and poles at 33.6% and these are materials used without the knowledge of their strength and properties. Hence, the need to assess its strength so as to protect the inhabitants against accidents and loss of lives. Research findings indicated that 100% of the structural design firms do not design masonry structures made of burnt clay bricks but instead specify them as infills. 100% survey on 102 sites established that the commonly used mortar mix ratios range between 1:7 to 1:14 far different from the perceived mortar mix ratios of 1:3 to 1:6 as a result of the use of one bag of cement to a number of wheelbarrows and these resulted into a compressive strength of 5.92N/mm2 to 1.87N/mm2 respectively far below the intended compressive strength of 17.8N/mm2 to 6.82N/mm2. Experimental tests on burnt clay bricks has established varying compressive strength with an average of 7.3N/mm2 to 2.06N/mm2 and this was attributed to water absorption, method of manufacture and the soil type. Results on burnt clay masonry walls constructed of most used mortar mix ratios established that , the compressive strength of the wall greatly reduced with increasing value of mortar mix ratios. Conclusively, the wall strength was much influenced by the strength of mortar, indicating that the weaker the strength of mortar the weaker the wall strength and vice versa however strong the brick may be, hence high mix ratios beyond 1:6 should not be used in the construction of masonry clay brick walls to avoid structural failures.