| This study had several objectives, including studying the effects of aggregate type and climate on creep and shrinkage losses, determining and quantifying the effects of moist-curing concrete (after prestressing), and proposing necessary revisions to the current AASHTO equations for creep and shrinkage loss prediction. In Reno and Las Vegas, twelve post-tensioned concrete beams made with local aggregates were monitored for creep and shrinkage losses along with a number of cylinder specimens that were monitored for creep and shrinkage strains independently. At each location, two box girders were left indoors exposed to a more stable environment, and two box girders and two solid beams were left outdoors exposed to precipitation and a wider varying environment. Of each pair of beams, one beam was kept moist for two weeks after prestressing (moist-curing) and one beam was not.; Testing and analysis found that moisture can increase the stiffness of aged concrete by 20%, possibly reducing creep and shrinkage losses. Aggregate type was found to influence concrete susceptibility to creep and shrinkage losses and the effects of moisture. Testing and analysis also found that in some cases the lifetime creep and shrinkage losses calculated from measured extrapolated surface strains exceeded the losses predicted by current prestress loss prediction methods from AASHTO, Naaman, and Nawy. Based on these findings, necessary revisions to the AASHTO equations for creep and shrinkage losses were proposed. |
