Recalibration of the Unit Strength Method for Determining the Compressive Strength of Grouted Concrete Masonry

Abstract

Using research that is now several decades old, the current Canadian masonry design standard, CSA S304.1-04, prescribes values for masonry design compressive strength based on the compressive strength of the concrete masonry unit and the type of mortar used in construction. The quality of unit production, masonry construction methods, and the theoretical understanding of masonry behaviour have improved significantly since these values were developed. As a consequence, current CSA S304.1-04 correlations between unit and masonry compressive strength values no longer reflect modern masonry construction and have been shown to be too conservative. In this investigation, 140 concrete masonry prisms were constructed for compression testing to recalibrate the tabulated unit strength values. An update to CSA S304.1-04 is proposed which includes strength increases of 33-40% for prisms with type N mortar, 10-30% strength increases for prisms with type S mortar and low unit strength, and 0-12% decreases with high unit strength.