Hadly G. Eisenbeisz, South Dakota Department of Transportation
The South Dakota Department of Transportation’s first use of high performance concrete (HPC) in an entire superstructure became a reality in the summer of 1999 with the construction of a railroad overpass structure on northbound I-29. This location was chosen mainly because high traffic counts and heavy use of deicing salts provided a true test of the strength and durability of HPC. Also, a twin bridge on the southbound lanes of I-29 was scheduled for construction in the summer of 2000, and would serve for comparison purposes and additional research.
The first step in the bridge project was selection of the research team. South Dakota School of Mines and Technology did trial batches and testing to optimize mix designs for the girders and the deck. South Dakota State University instrumented, monitored, and tested the girder and deck concrete during and after construction.
The bridge consisted of a typical three-span precast, prestressed concrete girder bridge with our standard integral abutments and integral bent diaphragms. AASHTO Type II girders were used for the 54-ft (16.5-m) long end spans and the 61-ft (18.6-m) long main span. The use of HPC allowed designers to reduce the number of girders in each span from five to four. Design compressive strength of the girder concrete was 9900 psi (68.3 MPa) with a strength of 8250 psi (56.9 MPa) required at release of the strands. The deck utilized a 4500 psi (31 MPa) compressive strength concrete. To improve durability, the cementitious materials in the deck concrete consisted of cement (75%), fly ash (17%), and silica fume (8%).
The girders were fabricated with a concrete containing silica fume and having a watercementitious materials ratio of 0.25. Several trial batches and test placements were performed by the fabricator to obtain the desired early strength and workability. The girders were moistened continually with soaker hoses and covered with polyethylene sheeting until the release strength was achieved. Deck specifications included a trial placement and the use of fogging behind the bridge deck finishing machine. Curing was required for a minimum of seven days using wet burlap, soaker hoses, and polyethylene sheeting.
The future of HPC looks promising in South Dakota. The twin southbound bridge was also constructed using HPC. Both bridges are instrumented and are being monitored to evaluate the performance of HPC. South Dakota bridge design engineers continue to use higher strengths for precast, prestressed concrete girders, and the use of fly ash in bridge decks is becoming a standard for durability.
Further Information
For further information or a copy of the research report, contact Hadly Eisenbeisz at [email protected].