Browsing by Subject "Autogenous deformation"
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Item Evaluation of volume changes and cracking potential of low water-to-cementitious material ratio concrete mixtures(2015-08) Tiburzi, Nicolás Bruno; Folliard, Kevin J.; Drimalas, ThanosThis 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.Item Multi-scale characterization, implementation, and monitoring of calcium aluminate cement based-systems(2012-05) Bentivegna, Anthony Frederick; Folliard, Kevin J.; Ideker, Jason H.; Fowler, David W.; Juenger, Maria; Wheat, HarovelCalcium aluminate cement (CAC) is a rapid hardening cementitious material often used in niche concrete repairs where high early-age strength and robust durability are required. This research project characterized the implications of the additions of various mineral and chemical admixtures to plain CAC to mitigate strength reductions associated with conversion, an inevitable strength reduction associated with the densification of metastable hydrates (CAH10 and C2AH8) to stable hydrates (C3AH6 and AH3). The effect of these admixtures on early-age strength development, volume change, and the correlation to macro-scale performance were reported in this dissertation. Various mixtures of CAC were investigated including: pure CAC, binary blends of CAC with fly ash (Class C) or CaCO3, and ternary blends of CAC with slag and silica fume. Characterization of the influence of these admixtures on hydration was completed using x-ray diffraction, isothermal calorimetry, and chemical shrinkage. Investigations on the implications of early-age volume change were conducted for autogenous deformation. In addition to laboratory testing, the final phase of the project was to correlate and elucidate the data generated in the laboratory to real-world field performance. Field trials were conducted to evaluate and monitor the behavior of CAC systems and investigate the link between laboratory generated research and actual large scale behavior.