Predicting Grouted Concrete Masonry Prism Strength

The structural performance of masonry is in part influenced by the relative and absolute compressive strength of the units, mortar, and grout. However, during the period immediately following masonry construction, the compressive strength of a given assemblage is often uncertain, as these materials have had insufficient time to fully cure. Further, with a near infinite number of combinations of unit, mortar, and grout strengths, designers have historically had little guidance related to available individual component properties when selecting a specified compressive strength of masonry for design purposes. In response to these needs, this paper analyzes a database of prism compression tests, which incorporate varying material properties into their construction. Based on the results of the prism tests, a prediction model is proposed that provides a correlation to the unit strength, mortar type, grout strength, and prism configuration to the measured prism compressive strength at varying ages of curing. The prediction model is based on 14 sets of prisms that were constructed and tested to meaure the influence of age on the strength of grouted masonry prisms. The prisms were all constructed using the same materials and construction methods and were tested at ages of 0, 1, 2, 3, 4, 5, 6, 7, 14, 21, 28, 35, 42, and 56 days following grouting. Additional 28-day strengths of grouted prisms from other research programs were used to validate the model and to further correlate the influence of mortar type, unit strength, grout strength, and prism configuration on the measured versus predicted prism strength.