Mathew Royce, New York State Department of Transportation
New York State Department of Transportation (NYSDOT) implemented the use of high performance concrete (HPC) for bridge beams with the completion of three bridges in 2001. An additional 19 bridges are now in various stages of design or construction. More than half these bridges will be completed by the end of 2002; the remainder will be completed in 2003.
Based on the experience with concrete Class HP for bridge decks* and with HPC for precast, prestressed concrete beams, NYSDOT is convinced that the use of HPC in bridge beams is good value based on life-cycle costs. NYSDOT is starting with a few HPC bridges with the plan of using HPC for all prestressed concrete bridge beams within a few years.
NYSDOT developed the specification for HPC in bridge beams, in consultation with the Precast Concrete Association of New York. Their main concern was the potential for rejection of beams due to test results slightly outside the specified range. The specification reduced this problem without impacting the quality and performance of the final product by allowing precasters to develop mix designs and to demonstrate in preproduction testing that the required performance criteria are met.
Precasters who are interested in producing HPC bridge beams for NYSDOT are expected to develop their own mix designs and submit them for approval. To initiate the process, a mix design sheet showing the proposed HPC mix design, proposed curing method during production, details of test specimen preparation, and information about the independent AASHTO accredited testing laboratory must be submitted to the NYSDOT. The test specimens are then prepared at the precasting plant and tested by the independent laboratory using the specified test method. The results are compared with the acceptance criteria and, if found acceptable, the mix design is approved for producing HPC bridge beams for any future NYSDOT projects.
For preproduction acceptance, the test mix must meet the following criteria:
Compressive strength (f’c) at 56 days (AASHTO T 22) ≥ 10,150 psi (70 MPa)
Modulus of elasticity when f’c ≥ 10,150 psi (ASTM C 469) ≥ 4351 ksi (30 GPa)
Shrinkage at 56 days (AASHTO T 160) < 600 millionths
Specific creep at 56 days (ASTM C 512) ≤ 0.41 millionths/psi (60 millionths/MPa) Freeze-thaw durability (AASHTO T 161 Proc. A) ≥ 80%
Scaling resistance (ASTM C 672) ≤ Rating 3 Chloride penetration (AASHTO T 259 Modified) ≤ 0.025% at 1 in. (25 mm)
Air content selected by contractor ≥ 3%
Water-cementitious materials ratio selected by contractor < 0.40
For acceptance of HPC during production, each batch ticket is examined to ascertain that mix ingredients and mix proportions are according to the approved mix design; AASHTO TP 23 is performed to ascertain that the water-cementitious materials ratio conforms to that of the approved mix design; air content is verified to be within tolerance; and the average concrete compressive strength for each beam is at least 10,150 psi (70 MPa) with no individual value less than 9650 psi (66.5 MPa). Monitoring of the other properties for the production concrete is an ongoing project by NYSDOT.
In addition to enhancing the durability, our designers are using the 10,150 psi (70 MPa) compressive strength concrete to design bridges with fewer girders to reduce cost or to design shallower superstructures to overcome vertical clearance limitations.
In conclusion, the overall experience of NYSDOT with HPC for prestressed concrete bridge beams is a positive one. If this success continues, NYSDOT will start specifying HPC for all prestressed concrete bridge beams within a year or two. The end result will be full-scale implementation of HPC in both beams and decks.