Workers on the Bill Emerson Memorial Bridge are watching the sky and the thermometer in hopes of ideal weather for the final construction stages.

With recent heavy rainfall moving out Wednesday, their focus can turn to grouting the cables and applying a 3-inch driving surface to the center 2,086 feet of the new bridge over the Mississippi River.

Scott Meyer, district engineer with the Missouri Department of Transportation, announced a completion date of Dec. 13, weather permitting. He said progress of grouting and surface work would be the determining factors.

On Wednesday, MoDOT area engineer Stan Johnson stood on the bridge approach in Cape Girardeau and explained those processes.

Grouting the cables

The white material around the steel cables is a high-density polyethylene casing, and that is what bridge-watchers can see gleaming from miles away. Inside that casing are strands of steel cable -- 19 to 55 strands, depending on how much weight must be supported at a certain location -- which are covered in plastic sheathing, Johnson said.

Grout, which is a mixture of cement, sand and water, must be pumped between the polyethylene casing and the plastic sheathing.

"It binds all the cables together so they work as one unit," Johnson said. "The cables hold the riding surface, and the piers hold the cables."

The grout is pumped through holes in each casing in three phases beginning at the bottom. The temperature can't drop below 40 degrees for the process, and the grout must stay dry. There are 171 miles of cable on the bridge, according to MoDOT's Web site.

Pavel Pavlov, an engineer with the French bridge cable construction firm Freyssinet, said the polyethylene casing provides an extra layer of protection.

"The grade of the steel is very high, very strong," he said. "But it also rusts pretty easily."

Driving surface

The final step will be applying a 3-inch driving surface to the cable-stay portion of the bridge. The approach will be regular concrete, but the special driving surface will contain silica fume, Johnson said.

The Silica Fume Association's Web site, www.silica fume.org, says the material is a "byproduct of producing silicon metal," and "concrete containing silica fume can have very high strength and can be very durable."

Johnson said silica fume concrete hasn't been used in this MoDOT district before, but it has an estimated life of 50 years.

The temperature can't exceed 85 degrees or dip beneath 40 degrees while the special concrete is applied, and the weather must be dry.

Members of the Cape Girardeau City Council marveled at the bridge while on a tour with Johnson on Wednesday.

Councilman Jay Purcell took his first steps onto the bridge.

"This like what you see in a major, major city," he said, looking upward at the white suspension cables and gray towers.

Staff writer Mike Wells contributed to this report.

hhall@semissourian.com

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