Airport Way South Viaduct

Seattle, WA

The Airport Way South Viaduct project was developed to rehabilitate an aging structure that is on a principal arterial for the City of Seattle.  The original viaduct was constructed in 1929 to provide a grade separation between the roadway and rail lines.  The structure was determined to be insufficient for the current volume and loads of vehicles utilizing it.

The original timber approach spans were replaced with structural earth walls.  For the 825’ main span, the original steel substructure was rehabilitated and received seismic improvements.  The deck consisted of precast concrete winged-channel beams with a CIP concrete overlay.  In order to meet the dead-load limits of the rehabilitated sub-structure, the winged channel beams required a custom cross-section and a controlled-density concrete mix.

Concrete Technology worked with the designer to establish an economical cross-section that would meet the load limits of the project.  A custom form was used to fabricate 210 pieces of winged channel beams that were approximately 8’ wide and 24’ long. 

Concrete Technology also developed a new controlled-density concrete mix that required 125 pcf density (unreinforced), 7,500 psi release strength and 9,000 psi strength at 28 days.  The concrete mix consisted of expanded shale coarse aggregate, normal-weight sand, cement and fly ash.


Custom cross section, precast concrete winged-channel beam

Controlled-density concrete mix


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