Drying shrinkage of ternary blends in mortar and concrete

Wang, Xuhao
Major Professor
Kejin Wang
Peter C. Taylor
Committee Member
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Civil, Construction, and Environmental Engineering

The work presented in this thesis involves the study of drying shrinkage behavior of mortars and field concrete mixtures made with ternary cementitious blends. The thesis is composed of two papers resulting from the study: (1) Short-Term Drying Shrinkage of Ternary Blends and (2) Drying Shrinkage of Ternary Blends for Use in Transportation Structure. In the former, statistical response surface analysis was employed to develop shrinkage models to better understand the drying shrinkage behavior of mortar mixes made with ternary blends. In the latter, ternary blend concrete mixtures used for pavement and bridge deck structures in different states were selected. Factors affecting drying shrinkage behavior of these ternary blend concretes were also investigated.

In Paper 1, shrinkage behavior of mortar mixes made with various ternary blends was studied. Ternary blends consisting of different combinations of portland or blended cement, slag cement, fly ash (Class C and F) and/or silica fume were considered: the amounts of slag cement, fly ash and silica fume ranged between 15-35%, 13-30%, and 3-10% by mass of cementitious, respectively. Mortar bars were made with the ternary blends and subjected to a drying condition (i.e., T = 73 y 3 yF and RH = 50y4%) after standard curing for 28 days. Free shrinkage of the mortar bars was measured up to 28 days. Based on the test results, a response surface analysis was done to examine the effects of blend proportions on shrinkage behavior of the mortars and a statistical model was developed for predicting the mortar shrinkage behavior. Furthermore, to validate the models, shrinkage strains of an independent group of mortar mixes were measured, and the measured values were compared with the predicted values. The results indicated that among the three supplementary cementitious materials in the ternary blends studied, slag cement showed a dominant effect on mortar shrinkage. The contribution of Class C fly ash to the mortar free shrinkage was slightly less than that of slag cement. Increasing silica fume content slightly increased free shrinkage, while an increase in Class F fly ash content slightly decreased free shrinkage of the mortar. There was a good correlation between the measured shrinkage strain and the strain predicted from the shrinkage model developed from the response surface analysis.

The work discussed in Paper 2 investigated the drying shrinkage behavior of ternary blend concretes that were used in transportation structures. Factors affecting drying shrinkage behavior of ternary blend concretes were studied. Five concrete mixes, used for either pavement or bridge deck construction, were tested for both restrained and unrestrained shrinkages. The effects of blend materials and mix proportion on the concrete shrinkages were assessed. The results indicated that shrinkage strain rate linearly increased with clay content of fine aggregate, cementitious material content, paste-to-void ratio (by volume), and dosage of water reducer of the concrete mixes.

The study demonstrates that the supplementary cementitious materials (SCMs) can be used to develop a statistical model in order to quantitatively predict drying shrinkage strain. The study gives a better understanding on how SCMs affect mortar and concrete drying shrinkage behavior. Both free and restrained shrinkage methodologies provide efficient analyses on interacted drying shrinkage influence factors. The cracking potential derived from restrained ring shrinkage test can be used to predict drying shrinkage cracking potential of ternary blend concrete mixtures.