The Hoover Dam and Lake Mead are located in Black Canyon on the Colorado River in the USA on the borders of Arizona and Nevada. Construction of the 220m high dam began in 1931 and more than 4 million m³ of concrete were placed by the time it was completed in 1936. Highway 93 is built into the top of the dam to cross the canyon, but the sharp bends and narrow widths of the highway, combined with the number of tourists and necessary security, led to an astronomical increase in traffic, so that long delays and bottlenecks had become the norm.
After a long debate due to the sensitive environment, the final decision was for a composite bridge structure with a reinforced concrete deck, over steel box girders, supported on concrete piers from twin concrete rib arches. For the cast-in-place reinforced concrete foundations and ribs of the arch, a High Performance Concrete mix design was specified that had to achieve a compressive strength of 69 MPas (10’000 psi), together with strict limits on shrinkage and longterm creep.
This had to be developed and then adapted to provide consistent performance in the extreme temperature conditions, which can vary from below -20°C in winter, to higher than +40°C in summer.
All of the engineers High Performance Concrete (HPC) requirements were met using Sika® ViscoCrete® Technologies. Sika’s concrete technicians worked closely with the engineers, the contractor and the concrete producer to ensure the specified consistence, performance and finish.
Sika® Rapid Technology was used for accelerated hardening to achieve the high early strengths of over 30 MPas within 16 hours where required, to enable the formwork to be stripped and accommodate early loading. For the segmental adhesive the engineers selected Sikadur®-31 SBA (Segmental Bridge Adhesive), as Sika is the global leader in this field and has previously completed numerous projects with Obayashi and others in China, Japan, the USA and worldwide.
Finally the necessary cable grouting around the post-tensioning tendons in their ducts, was successfully completed using the well known Sika-Grout® PT system, which was developed by Sika USA as members of the American PTI (Post Tensioning Institute).
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USA Government, Federal Highways Department
HDR Services Inc. & T. Y. Lin International
Joint Venture of Obayashi Corporation and PSM Construction
Concrete Producer – Ready-mix
Casino Readymix Inc.