High performance concrete applications in bridge structures in Virginia

This paper summarizes current work in high-performance concrete (HPC) in bridge structures by the Virginia Department of Transportation (VDOT). VDOT has planned 5 bridge structures using HPC for construction in 1995 and 1996. In four of these structures high strength concrete will be used in AASHTO prestressed beams. Three of the structures will have concrete with a minimum 28 day compressive strength of 55 MPa (8,000 psi) and a release strength of 41 MPa (6,000 psi), and the fourth will have beams with 69 MPa (10,000 psi) at 28 days and 46 MPa (6,600 psi) at release. The beams on the fourth structure will contain 15 mm (0.6 in) diameter strands. Beams on the other three structures will have 13 mm (0.5 in) strands. All strands will be at the 51 mm (2 in) spacing. The concrete in three of the bridges will meet the VDOT's new proposed low permeability concrete requirement of 1,500 coulombs or less for the prestressed members, 2,500 coulombs or less for deck slabs, and 3,500 coulombs or less for concrete substructures. One bridge utilizing HPC will be constructed with steel beams but with its deck and substructure meeting the low permeability requirements. Construction began in early 1995 on two of the bridges with 55 MPa (8,000 psi) strength at 28 days. Before the bidding of the first of the structures with 55 MPa (8,000 psi) concrete, an experimental project was conducted to ensure that high release and ultimate strengths could be achieved. Four 9.4 m (31 ft) long AASHTO Type II beams were prepared and tested to failure. Similarly, before the advertisement of the bridge with beams containing 69 MPa (10,000 psi) at 28 days and 15 mm (0.6 in) strands, two 9.4 m (31 ft) beams with fully composite slabs were prepared and tested to failure.