Evaluation of volume changes and cracking potential of low water-to-cementitious material ratio concrete mixtures
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This thesis presents the results of a comprehensive evaluation of volume changes and cracking potential of low water-to-cementitious materials ratio concrete mixtures. This work was initiated due to observed cracking of prestressed concrete beams in Texas that typically becomes visible after one to two years of service. This study evaluated various forms of volume change, including chemical shrinkage, autogenous shrinkage, and drying shrinkage. A subset of the mixtures from this study was evaluated using a restrained shrinkage frame, where the stress development was monitored along with the development of mechanical properties. A range of materials and mixture proportions were evaluated, including various portland cements, supplementary cementitious materials, aggregate types, and high-range water reducer types. Overall, it was determined that the most important parameter determining cracking potential was the volume change caused by autogenous deformations at early ages. The results of the laboratory investigations were complemented by large scale exposure blocks that were stored outdoors in Austin, TX. Only a small number of blocks cracked during the course of this study, but the long term behavior of these blocks will continue to be monitored to better correlate laboratory results to field performance.