A study of prestress losses of post tensioned beams cast with self compacting concrete and conventional concrete

Abstract

Self-compacting Concrete (SCC) can be cast without mechanical vibration and is therefore useful for the precast and prestressed concrete industry. Research on the time-dependent prestress losses of SCC prestressed members are very limited. Hence, this research is undertaken to investigate and compare the prestress losses of similar SCC and conventional concrete (40 MPa) prestressed beams experienced at transfer, after transfer and during service. Two sets of beams, one each subjected to high and low prestress levels were tested. In all four full size simply supported prestressed beams were tested, two cast using SCC and the other two cast using conventional concrete. Also included in the study were creep and shrinkage tests on cylindrical concrete specimens to obtain the creep and shrinkage properties of both concrete mixes used in the study. The creep and shrinkage of the SCC mix was 20 - 30 % higher than that of conventional concrete mix. The loss in tendon strain of the SCC beams was higher at transfer and lower after transfer for a duration of 22 days thereafter. All beams showed insignificant prestress losses during service and have very similar ultimate loads.