Determination of stress relaxation parameters of concrete in tension at early-age by ring test

In this paper, the ring test is used to determine the stress relaxation parameters of concrete in tension at early-age. Through ring test, the steel–concrete interfacial compressive stress generated from shrinkage of concrete is obtained first. Meanwhile, the theoretical value of the interfacial compressive stress is precisely calculated by a model for given shrinkage of concrete. In the model, a power function with three unknown constants was used to model the viscoelastic behavior of concrete under tension. The expected stress relaxation constants can then be determined with the condition that the difference between calculated and tested interfacial compressive stresses satisfies the required tolerance. Using this mythology, the creep relaxation parameters of three kinds of concretes with compressive strength at 28 days around 30 MPa, 50 MPa and 80 MPa are obtained. The determined stress relaxation parameters are used in the existing experimental results of shrinkage stress tests that are independently carried out and reasonable agreement between model and test data is found.