Creep, shrinkage, and cracking of restrained concrete at early age

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 mechanisms. Effects of fiber reinforcement (steel and polypropylene), water-cement ratio (w/c), drying conditions, and curing conditions on restrained shrinkage behavior of normal concrete (NC) and high-performance concrete (HPC) are discussed. It was found that tensile creep relaxed shrinkage stresses by 50% and doubled the failure strain capacity. Both the magnitude and time history of the shrinkage stress influence the rime of cracking, which in this study occurred at approximately 80% of the static tensile strength. Steel fibers substantially delay the shrinkage cracking, but without influencing the stress at failure. Finally, it was found that sealing of the concrete specimens did not eliminate the early age shrinkage, and that wet curing effectively relaxed shrinkage stresses.