Creep Behavior of Self-Consolidating Concrete
Type of DegreeThesis
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Self-consolidating concrete (SCC) is a highly flowable material that has the ability to improve the quality and durability of structures; however, much is still unknown about the hardened properties of this material, including the creep behavior. This thesis presents research aimed at improving knowledge in this area by investigating the creep performance of four SCC mixtures and one conventional-slump mixture. The four SCC mixtures have varying water-to-cementitious materials ratios of 0.28 and 0.32, and use differing powder combinations that include Type III portland cement, Class C fly ash, and Ground Granulated Blast-Furnace (GGBF) slag. All four SCC mixtures’ fresh properties were evaluated using the slump flow, T-50, and VSI tests. For each mixture, the following five loading ages were investigated: 18 hours, 2 days, 7 days, 28 days, and 90 days. The 18-hour samples, which had compressive strengths ranging from 5,800 psi to 8,860 psi, were cured at predetermined elevated temperatures that are typical of those used in the prestressing industry in the Southeastern United States. The samples loaded at 2, 7, 28, and 90 days were moist cured prior to loading. Upon the completion of curing, each sample was loaded to achieve a stress level equal to 40 percent of the concrete compressive strength. All data collected from the SCC mixtures were compared to the data from the conventional-slump mixture. When curing was accelerated and the load was applied at 18 hours, the creep of all the SCC mixtures was less than the conventional-slump mixture. All SCC mixtures cured under elevated or standard laboratory temperatures exhibited creep values similar to or less that of the conventional-slump concrete mixture. When curing was not accelerated, the creep behavior of the moderate-strength fly ash SCC and conventional-slump mixtures were similar. The high-strength mixtures had the highest paste content, but exhibited less creep than any of the moderate-strength mixtures. At a fixed water-to-cementitious materials ratio, SCC mixtures made with GGBF slag exhibited less creep than those made with fly ash, regardless of the age at loading. The accuracy of the following five creep prediction methods was also investigated: ACI 209, AASHTO 2007, CEB 90, GL 2000, and B3. ACI 209 provided the most accurate creep estimations for the accelerated-cured specimens, except for the high-strength concrete mixture. The AASHTO 2007 method underestimated the creep at early concrete ages, but overestimated it for later ages. Overall, the CEB 90 method was the most accurate of the five models investigated in this study. The GL 2000 and B3 methods significantly overestimated the creep for all mixtures.