Effects of Accelerated Curing on the Time-Dependent Properties of Concrete

Thesis (Master's)--University of Washington, 2018The long-term creep and shrinkage behaviors of concrete can greatly affect the serviceability and constructability of prestressed concrete structures. To account for these effects, it is necessary to reliably predict the deformations of the concrete through time. These calculations are particularly challenging for precast, prestressed girders, for which fabricators often use accelerated curing regimes (hot-curing) to make the concrete gain strength faster and thus increase girder production rates. With the exception of a recent study at the University of Washington (Magnuson 2016), little data previously exists on the creep and shrinkage behavior of concrete for such a curing regime. Current prediction models of creep and shrinkage have been calibrated using ambient-cured concrete tests and assume a constant stress history. They deal with variable stress histories by applying the principle of superposition. The validity of the application of the principle of superposition to creep strains has been questioned by many, and it is not computationally convenient. The objectives of this research were (1) to collect additional data on the creep and shrinkage of hot-cured concrete, (2) to study the effect of hot-curing concrete further and (3) to validate the functionality of a model proposed by Magnuson. The additional data verified that creep is affected by the hot-curing but it suggested that shrinkage strain are not affected. Several configurations of the model were calibrated, and a reasonable fit was achieved to creep data from concrete with a diverse set of loading histories. A previously suggested and simpler version of the model showed comparable results (but slightly worse), which questions the necessity of the more complex version of the model