Effects of different mortar mixes and soil composition of Burnt earth bricks on the compressive strength of masonry walls.

Abstract

Burnt earth bricks are widely used in low developing countries such as Uganda as one of the elements in the construction of masonry walls. However, no information is available about their properties such as compressive strength, soil composition, and as well as the strength of the resultant masonry wall in relation to mortar strength. This has resulted in erecting of masonry walls whose strength is unknown which is dangerous in terms of safety of the occupants and economically unviable. This study investigates the effects of different mortar mixes and soil composition of Burnt earth bricks on the compressive strength of the masonry walls. Soil samples and Brick units were collected from four brick-making kilns around Kampala and tests were carried out: sieve analysis and hydrometer analysis carried out to establish the soil composition in terms of particle size distribution, Atterberg limits, compressive strength test on the brick units to establish the strength of the bricks. Also, compressive strength tests were performed on different mortar mixes and masonry wallettes. Results of this research revealed that the clay content in the soil samples from four brick-making sites around Kampala which contributes to the strength of burnt earth bricks was as follows: sample A (Kazo Angola) - 62%, sample B (Kazo central 1) - 60%, sample C (Jinja Kaloli) - 60% and sample D (Bweyogere) - 71% and their average brick strength was: 2.1〖N/mm〗^2, 1.3〖N/mm〗^2, 0.8〖N/mm〗^2 and 1.6〖N/mm〗^2 respectively. The compressive strength of burnt earth bricks obtained from the different brick making sites around Kampala varied greatly from 2.1〖N/mm〗^2 to 0.8〖N/mm〗^2 averagely respectively. The compressive strength of mortar mix ratios used was found to be 16.8〖N/mm〗^2 for 1:3, 9.1〖N/mm〗^2 for 1:5, 3.4〖N/mm〗^2 for 1:7 and 2.7〖N/mm〗^2 for 1:10. The masonry walellettes’ failure occurred in bricks instead of mortar joints which is not a safe design since the burnt earth bricks' average strength used varied from 2.1〖N/mm〗^2 to 0.8〖N/mm〗^2 which is far less than the mortar strength. The strength of mortar should not be greater than the strength of bricks because mortar is more flexible and cracks in mortar are easy to repair. The average strength of wallettes tested varied from 1.06 〖N/mm〗^2 to 0.62〖N/mm〗^2 , 1.10〖N/mm〗^2 to 0.78〖N/mm〗^2, 1.14〖N/mm〗^2 to 0.84〖N/mm〗^2, 1.19〖N/mm〗^2 to 0.91〖N/mm〗^2 averagely for samples C, B, D, A for mortar ratios 1:3 and 1:10 respectively. The resultant wall strength was much influenced by the strength of bricks. Wall strength is affected by the mortar mix ratios, that is to say; wall strength increases with an increase in the mortar strength.