Effect of vertical strand location on bond performance of prestressing strands cast in lightweight self-consolidating concrete

Abstract

The high fluidity of lightweight self-consolidating concrete (LWSCC) combined with the tendency for some aggregate particles to collect near the top of the member has the potential to affect bond of prestressing strands with a significant amount of concrete below. Transfer and development length were evaluated for rectangular beam specimens cast with LWSCC and normal weight self-consolidating concrete (SCC). Each member was prestressed with a single 13.3 mm prestressing strand and cast with 300 mm of concrete either above or below the prestressing strand. Strand end slip was used to compare prestress transfer behavior, and measured transfer lengths were compared to the ACI and American Association of State Highway and Transportation Officials (AASHTO) equations. Development length was evaluated using flexural tests with a critical section at the code calculated value. The results of the experimental program indicate an increase in transfer length for strands placed near the top of the members cast with SCC. The ACI/AASHTO equation and AASHTO 60db expression produced reasonable average predictions for transfer length of bottom strand specimens, but underestimated transfer length for top strand specimens. Flexural tests indicated a development length larger than the value predicted using the ACI and AASHTO code equations for specimens with 300 mm of concrete below.