HPC for I-235 Bridge Reconstruction in Iowa

This paper describes how a committee from the Iowa Department of Transportation (DOT) and the Iowa FHWA office began exploring the use of high performance concrete (HPC) for bridge projects in the reconstruction of I-235 in 1999. The initial expectations for HPC were reduced permeability, increased durability, strength when needed, and reduced cracking. To achieve these expectations, the committee evaluated concrete mix proportions, materials selection, timing and duration of curing, winter placement practices, and placement size and sequence. The committee also identified specific performance criteria for the substructure components; precast, prestressed concrete beams; deck; and barrier rails. In 2000, the Office of Materials began evaluating the standard Iowa DOT mix designs for cast-in-place concrete and precast, prestressed concrete. The standard mixes were improved by reducing the water-cementitious materials ratio, adding supplementary cementing materials, and improving aggregate gradation, while testing for strength, permeability, and cracking tendency.