Drying Shrinkage Behavior of Mortars Made with Ternary Blends

Ternary cementitious blends are widely used in today's concrete mixtures, particularly when high performance is needed. This paper discusses drying shrinkage behavior of mortar mixtures made with various ternary blends. Ternary blends consisting of different combinations of portland or blended cement, slag, fly ash, and silica fume were considered. The amounts of slag, fly ash, and silica fume ranged from 15% to 35%, 13% to 30%, and 3% to 10% by mass of cementitious materials, respectively. Mortar bars were made with the ternary blends and subjected to drying (i.e., temperature = 73° ± 3°F and relative humidity = 50% ± 4%) after standard moist curing for 28 days. Free shrinkage of the bars was assessed at 56 days of age after 28 days of drying. A response surface analysis was done to examine the effects of blend proportions on shrinkage behavior of the mortars. To validate this model, an independent group of mortar mixtures with different ternary combinations was cast, and the measured values were compared with the predicted shrinkage values. The results indicated that of the three supplementary cementitious materials in the ternary blends studied, slag showed a dominant effect on increasing mortar shrinkage. The contribution of Class C fly ash to the shrinkage was slightly less than that of slag. An increase in silica fume or in Class F fly ash content slightly increased free shrinkage. There is a good correlation between the measured shrinkage strain and the strain predicted from the shrinkage model developed from the response surface analysis.