Single-blade spec applied to concrete surface saves costs on WSDOT floating bridge project

May 18, 2017
Single-blade spec applied to concrete surface saves costs on WSDOT floating bridge project

The Evergreen Point Floating Bridge, also known as the 520 Bridge or its official name of the Governor Albert D. Rosellini Bridge, spans Lake Washington from Seattle to Bellevue and was replaced in 2016. The new bridge is certified by the Guinness Book of World Records as the longest and widest floating bridge in the world at 7,710 ft long and 116 ft wide.

The original bridge was built in 1963, and due to increased traffic as well as earthquake vulnerabilities, the bridge was in need of a full replacement. The new bridge consists of 77 concrete pontoons secured by 58 anchors to the lake bottom. The bridge deck is located on a platform raised 20 ft above the water, higher than the previous bridge. The road also includes shoulders and areas for pedestrian and bicycle traffic. The Washington State Department of Transportation (WSDOT) needed the bridge to last at least 75 years and provide a safe, quiet ride since it would be heavily trafficked and there are neighborhoods around the lake. The WSDOT decided the bridge deck and roads should feature one of the quietest concrete pavement textures, Next Generation Concrete Surface (NGCS).

NGCS is a hybrid texture that combines conventional grinding with longitudinal groove channels. The NGCS texture reduces road noise, creates a smoother ride, and increases drainage for better skid resistance and a safer roadway. Interstate Improvement Inc., based in Faribault, Minn., was awarded the NGCS grinding portion of the project. Interstate Improvement knew how important it would be for the NGCS texture to turn out perfectly as it would be the final surface on the world’s longest and widest floating bridge, and would therefore come under scrutiny for a long time. The team used a 3-pass method to ensure everything went smoothly and cuts were straight to ensure the final surface turned out as planned.

The first pass used a conventional grinding head, made up of 230-240 diamond blades stacked together with spacers between the blades, to remove all surface irregularities and to provide a baseline for the final ride profile. The second pass used a flush stacked head with minimal spacing to remove the conventional grind ridges or “fins” and any remaining rough spots from the pavement to leave a very quiet, smooth surface. The third and final pass was to cut longitudinal grooves to provide traction for vehicles and remove water from the roadway while at the same time keeping the quiet ride.

Interstate Improvement relied on a single-blade specification capable of grinding/grooving all three passes from Husqvarna Construction Products. Sam Gramling, President, Chief Operations Officer of Interstate Improvement said, “The single-blade spec greatly reduced the need to carry costly extra inventory, and allowed us to be flexible with a constantly shifting schedule.” The project turned out great and will make a fine addition to Lake Washington for many years to come.

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