Article and Photos by Todd Mittelstadt
Everyday distractions can prevent us from seeing, let alone appreciating, the beauty that exists around us. For example, people have admitted that the striking precast concrete design sculptures on the new I-35W bridge are easy to miss among the visual blur of overhead signage when traveling at highway speeds. Fortunately, the physical constraints of rush-hour traffic afford an excellent opportunity for drivers to take in the uplifting view of the unique 30-foot-high vertical waves that rise in stunning precast whiteness. In the center median at each end of the bridge, the three individual precast waves flowing upward are the I-35W Gateway Monuments.
Each precast wave is 1.5 feet wide and 5 feet deep with a total weight of about 56-tons for each three-wave element. The scale of these two elements might seem to contradict the possibility of missing them while traveling across the bridge. Yet the natural contour of the design blends into the bridge rather than overtly projecting its presence. Oslund and Associates, working with Figg Engineering and a Mn/DOT advisory group, designed the monuments as part of the overall landscape. Their project description best explains the design: “The symbol for water, inverted on its side, simply defines the transitions of the road on land to a bridge over water – a sound pairing to the quiet design of the bridge.” Cemstone Companies and Stoneworks Architectural Precast collaborated to create the Gateway Monuments.
Another unique attribute of the monuments was the use of TX Active, a white photocatalytic cement. Natural sunlight activates the photocatalytic reaction within concrete made with TX Active cement. The reaction accelerates the oxidation of pollutants and prevents them from accumulating, obtaining a “selfcleaning” effect. Application of this new cement technology will keep the precast monuments a bright white color. This pollutant oxidation benefit is not limited to surface contamination but it also removes carbon monoxide, nitrous oxides and sulfur dioxide from the air surrounding the monument. Cemstone Companies claims that it was the first to use this material in North America, and its engineering services group was the first to develop a mix design for self-consolidating concrete.
Stoneworks Architectural Precast has built a reputation on its ability to create distinctive architectural precast products that capture the imagination of its clients. Once awarded the project, a 20-by-50-foot exterior concrete pad was poured to serve as the casting location. The formwork began soon after. It took three men approximately three weeks to construct the form. The form had to be capable of supporting the 56-tons that each piece would weigh. Additionally, it had to be capable of being disassembled and reassembled with very little rework to prepare for the second pour. The form consisted of 120 sheets of mill-certified plywood, 50 sheets of marine-grade plywood, and 50 sheets of furniture-grade aspen plywood. A sub-base made up of compartments with a 1.5-inch-thick top was constructed to support the load.
The curve of the waves provided some of the needed structure to support the hydrostatic pressure during the pour, and 4-foot-by-4-foot plywood gussets provided the rest. The aspen plywood used for the surface areas was finished with a fiberglass resin and then sanded smooth. Once bent into the shape of the waves, all seams were filled, sanded and finished smooth. The final finish for the monuments was smooth concrete. Kevin MacDonald, vice president of Engineering Services at Cemstone Companies, developed the self-consolidating concrete mix design that was based on Mn/DOT requirements for the I-35W Bridge. He further refined the mix to meet the flowability requirements of the formwork and final color appearance of the monuments. This outstanding project allowed everyone involved to capitalize on their strengths. For us at Stoneworks, this project offered an opportunity to highlight the company motto: “Translating a vision into concrete reality.”
Todd Mittelstadt is the director of operations for Stoneworks Architectural Precast Inc. of Elk River, Minn.