THE PICKETT EFFECT IN EARLY AGE CONCRETE UNDER RESTRAINED CONDITIONS

摘要

Creep and shrinkage of concrete under restrained conditions during the first days after casting have been characterized by experiments that provide data on shrinkage and tensile creep strains, restrained shrinkage stress and the extent of stress relaxation by tensile creep mechanism. Tensile creep of concrete has two major components- basic creep and drying creep. Drying creep, known as the Pickett Effect, is a component of creep that is not observed unless the concrete is exposed to drying conditions while under sustained load. We discuss experiments and analysis that shows that drying creep itself has two components. First, a term associated with stress-induced shrinkage, and second, a term associated with microcracking due to the non-uniformity of drying. Test results for normal concrete mixes with different w/c are discussed and related to general behavior. Effects of inclusion of steel fibers are explained.