POLYMER CONCRETE USED IN REDECKING A MAJOR BRIDGE. FINAL REPORT

The FHWA worked with MD DOT and Greiner Engineering Company to design pedestals of polymer concrete (PC) for supporting the precast deck elements on the Woodrow Wilson Bridge in Washington, D.C. Steel plates rested on the girders and stringers and polymer concrete was forced through 2-inch holes in the deck to form supporting pedestals approximately 9X14 in. with heights up to 6 in. Nelson studs tie the PC to the base plate and an inverted cone adds shear resistance between the pedestal and the lightweight concrete deck. Over 30 mixture designs were performed to formulate an adequate mixture based on a methylmethacrylate monomer containing dimethyl-p-toluidine as a promoter and powder aggregate containing benzoylperoxide as initiator, extended with graded stone. The ingredients were varied slightly to form a cold and a hot weather formulation. The specifications called for less than 0.10 percent shrinkage. Materials with a 15-minute worktime had typical compressive strengths which often approached 6000 psi at 1 hr. A major problem encountered was the shrinkage and gravity flow of the polymer concrete downward from the underside of the precast slab. Spaces as great as 1/8 inch over 50 percent of pedestal cross-section formed between the precast slab and the pedestal. Various schemes of form venting, vibration, forming and physically keying the slab to the pedestals were tried. The plan finally accepted was to create an inverted cone of polymer concrete, increasing from 2 1/2-inch diameter fill hole to a 6-inch diameter base at the bottom of the slab interface with the pedestal. Polymer concrete was also used to seat the expansion joints and to fill the joints between slabs during the longitudinal post-tensioning of the system.