Bonding Time and Prestress Loss in Precast Pretensioned Concrete during Steam Curing

Abstract

During steam curing of concrete, the axial restraint of pretensioned strands causes thermal prestress loss of the strands accumulated until sufficient bonding occurs. A theoretical model is presented in this paper to predict the progressive slippage of strands with time, bonding time, and the amount of thermal prestress loss. The model incorporating the equivalent age-dependent local bond-slip relationships considers the effects of material-related factors, the layout of the prestressing system, and changes in the temperature. Three pairs of two monostrand pretensioned concrete prisms were fabricated to validate the developed model. The model was able to trace the experimentally measured progressive slippage of the strand reasonably well, and it predicted thermal prestress losses by 5.2%–5.5% of the initial prestress of 1,395 MPa for the tested prisms.