Structural Lightweight Concrete Prestressed Girders and Panels

This report explores the uses of high performance lightweight concrete (f'c ≥ 6000 psi) in pretensioned girders and deck panels.

A summary of pertinent literature on application of lightweight concrete in bridge applications is given. The results indicate a number of successful applications as well as a few cautions. The development of 6000 psi and 7500 psi mixes using locally available materials and local precasting plants is outlined. Results indicated that 7500 psi was a highly dependable maximum. Workability of the mixes was adequate, and a series of beam sections, including some purposefully highly congested members, were sucessfully cast under plant conditions.

When applied in pretensioned girders, the transfer length for ½-in strands was found to be 40 percent longer than the AASHTO requirement. Development lengths, moment capacities, and load-deflection curves were very similar to those of normalweight concrete girders. Lightweight concrete use in precast deck panels indicated the transfer length of smaller strands was adequate. The full calculated ultimate moment capacity of girders with lightweight concrete deck panels was developed. Such panels could be used interchangeably with normalweight concrete panels using current design requirements as long as the flexural tensile stress limits under fluid deck load are satisfied.

The report recommends that AASHTO change the model for calculating development length for prestressing strand to an expression containing the concrete Modulus of Elasticity. This would make it applicable to both normalweight and lightweight concrete. A future report will discuss economic analysis factors.