Lübeck, André1; Mohamad, Gihad2; Fonseca, Fernando S. 3; Modler, Luis E. 4 and Schmidt, Raquel P. B. 5
1 PhD student in Civil Engineer, Federal University of Santa Maria, Brazil, andrelubeck@unipampa.edu.br
2 Adjunct Professor, Building and Structure Department, Federal University of Santa Maria, Brazil, gihad@ufsm.br
3 Associate Professor, Brigham Young University, Department of Civil and Environmental Engineering, 368 Clyde Building, Provo, Utah, USA, fonseca@byu.edu
4 PhD student in Civil Engineer, Federal University of Santa Maria, Brazil, luismodler@gmail.com
5 PhD student in Civil Engineer, Federal University of Santa Maria, Brazil, raquelbrondani@gmail.com
ABSTRACT
The study presented herein evaluated the influence of the mortar strength on the prism-block strength ratio and on the failure mode of axially loaded hollow concrete block masonry. The literature indicates that mortar strength has little influence on the masonry strength; however, it lacks information on the influence of the mortar strength on the failure mode of the masonry. To address this lack of information, two sets of prisms, two-blocks high, were constructed using one type of block and two different types of mortar: one with high strength (mortar-block strength ratio of approximately 1.0) and another with low strength (mortar-block strength ratio of approximately 0.15). In addition to measuring applied loads and deformations, the tests were monitored with a high definition camera, capable to shot 24-frames-per-second images, to observe the rupture sequence of the prisms. The net area average strength for the prisms with high-strength mortar was approximately 15.0 MPa and the prism-block strength ratio was 0.72. For the prisms with low-strength mortar, the average strength was approximately 14.0 MPa and the prism-block strength ratio was 0.67. These results agree with those of other researchers -mortar has little influence on masonry prism strength. However, the failure mode was very different. The prisms assembled with low-strength mortar failed due to mortar crushing, followed by generalized cracking and spalling of the blocks at the joint. The failure occurred at stress/strength levels of approximately 50%. Post-rupture evaluation showed a complete breakdown of the adhesion between the block and the mortar and destruction of the porous structure of the mortar. In contrast, the prisms assembled with high-strength mortar experienced typical conical breaks. The results of the research presented herein indicate that evaluating masonry strength regardless of its failure mode can result in strength overestimation and uncertain level of safety.
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