Bridge builders pour a tall, cool one
Cement mixers poured a tall, cool one at the Maroon Creek bridge construction site Tuesday.The roughly 90 cubic yards of concrete delivered for use in one of the piers that will support the new span required about 7.6 tons of ice cubes, loaded into cement mixers one 20-pound bag at a time.It’s a highly unusual step in the mixing of concrete for highway projects, at least in Colorado, but the massive piers that will support the bridge – they’re each about 10 square feet – require the kind of cooled concrete normally reserved for dams and other really thick concrete masses.In all, the bridge will require more than 8,000 cubic yards of concrete, according to Phil Long, a senior sales representative with LaFarge North America, which is supplying the material from its Woody Creek plant. Only the concrete used in the piers, however, will be mixed with ice.Basalt-based Aspen Cool Ice, a wholesale supplier affiliated with Big Nugget Ice Supply in Fruita, delivered 20,000 pounds of ice to LaFarge on Monday for the pier pour.Though Aspen Cool Ice supplies ice for such local events as the Jazz Aspen Snowmass festivals and the Aspen Food and Wine Classic, the LaFarge orders have been the largest the local supplier has ever had to fill, according to co-owner Terry LaFrenz.
“This is kind of a new application for us. It has been a bonanza for us, certainly,” he said. “We’ll hate to see the bridge completed.”A seemingly endless stream of plastic bags of ice were dumped onto a conveyor Tuesday for transfer into cement mixers – roughly nine trucks in all.In 26 years with LaFarge, this is only Long’s second “ice pour” in western Colorado. The other, he said, involved a thick, concrete coal storage silo.Among highway projects, the practice is more common in hotter climes.Temperature is key for the concrete piers that will hold up the new highway bridge spanning the Maroon Creek gorge on the outskirts of Aspen.Concrete heats up as it cures, or sets, and in the thick columns, the center will heat more quickly than the exterior without the ice to help maintain a more consistent temperature throughout the pier. Vast temperature extremes within the pier can result in cracking.
“On a big concrete placement like that, it can get pretty hot at the center,” said Joe Elsen, program engineer for the Colorado Department of Transportation in Glenwood Springs.Tuesday’s pour at the bridge site will be allowed to set for seven days before the outer forms are removed, when the temperature differential between the inner core and the outer surface is acceptable, according to Ray Schmahl, general manager of BTE, the contractor building the bridge.There are probes set within the concrete so the crew can track temperatures within the material as it cures.Temperature is a critical component at LaFarge, as well. Concrete is made in the cool morning hours and needs to be poured within 90 minutes after its mixed in the trucks that carry it to the job site.”With the ice pours, timing is even more critical,” Long said.”Making big margaritas out here, we are,” joked Adam Montover, plant manager and the man who oversees the complex formula for mixing concrete. The temperature of the air and each of the individual materials used in the concrete is measured, and the amount of ice necessary for the batches is calculated. The ice replaces most of the water used in the normal mixing of concrete, Long explained.
Given Tuesday morning’s air temperature, a typical batch of concrete mixed with water would likely have started out at 70-plus degrees, according to Montover. The loads of iced concrete were inching the mercury toward 50 degrees as the trucks pulled out of Woody Creek and headed for the bridge. “Perfect,” Long said.The roughly $17 million Maroon Creek bridge project – including almost $14 million for actual construction by BTE – is expected to wrap up in late 2007, according to Elsen.The four-lane bridge will be built in cantilevered sections of decking that will jut out from the piers until they eventually connect.Janet Urquhart’s e-mail address is firstname.lastname@example.org
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