1 Vice President of Engineering, National Concrete Masonry Association, Herndon, VA, U.S.A, jthompson@ncma.org
2 Manager, Research and Development Laboratory, National Concrete Masonry Association, Herndon, VA, U.S.A, nlang@ncma.org
3 Project Engineer, National Concrete Masonry Association, Herndon, VA, U.S.A, twitthuhn@ncma.org
ABSTRACT
The unit strength table in the Specification for Masonry Structures (TMS 602/ACI 530.1/ASCE 6) allows users to designate specific combinations of mortar type and concrete masonry unit compressive strength to achieve minimum masonry assembly compressive strengths for design application. This table can also be used for inspection purposes when verifying the minimum specified compressive strength of masonry, f’m, where the mortar type and unit compressive strength are known quantities. Compared to other options for verifying assembly compressive strength, the unit strength method can be easier and less expensive to implement. It is recognized, however, that the unit strength table is inherently conservative; providing assembly compressive strength values considerably lower than what would be expected for a given combination of unit strength and mortar type.
Drawing from a newly developed database of prism test data, this research investigation evaluates the correlation between unit strength, mortar type and assembly compressive strength. Based on this testing and analysis, a new unit/assembly compressive strength correlation is proposed that reflects not only contemporary materials and testing procedures, but unit compressive strength values that provide a more accurate assessment and predictor of assembly compressive strength for design application or field quality assurance.
KEYWORDS: specified compressive strength, prism testing, unit strength method, mortar type
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