Corps casts history in Louisiana
Concrete trucks, smoothers and a groover form a production train follow one another from row to row at the U.S. Army Corps of Engineers’ 229-acre concrete mat casting facility in St. Francisville, La. The yard recently cast its 11 millionth mat. (Photo by Angelle Bergeron)
The mats are used along the lower 325 miles of the Mississippi River and the upper 55 miles of the Atchafalaya River to provide flood protection and to prevent against erosion and meandering in others, said Don Rawson, project manager with the corps’ New Orleans District.
Articulated concrete mats are 3 inches thick, 4 feet wide and 25 feet long. They are held together by stainless steel wire and formed with spacing that allows the mats to flex, or articulate, to uneven surfaces, like the bottom of the river.
The mats are shipped by barge and then assembled with stainless steel fabric and tied together with copper-coated wire, creating all non-corrosive connections.
On July 10, a group of corps employees and retirees gathered at the St. Francisville Mat Casting yard to have celebratory lunch of jambalaya and watch Fordice Construction Co. of Vicksburg, Miss., cast mats.
Although mat casting is simplistic compared to the bridge, roadway and other heavy construction usually tackled by Fordice, the work requires a certain skill set and specially adapted equipment, said Dan Fordice, owner and vice president.
“We’ve adapted the frames of farm tractors to be able to straddle mats that are stacked 13 high,” Fordice said.
To make the mats, the equipment drives over the steel forms, which are laid on the ground.
“The first truck will lay 80 percent of the concrete,” Rawson said.
The concrete truck is followed by a smoother, then another concrete truck, which lays out more concrete to fill voids. That is followed by another smoothing machine, then a groover.
“The grooves ensure the mats provide good fishery habitat, good bio mass for algae, small fish and crustaceans,” Rawson said. “We had this on the MRGO (Mississippi River Gulf Outlet), and it had oysters growing on it. It provides a good home for marine life.”
The mat is covered with paper and sprayed with a biodegradable oil, which makes is easier to release the form. Within two hours, when the concrete is set, the forms are removed, said Ken Barr, construction representative for the corps.
“The next day, they will place the forms on top and do it again until the stack is 13 mats high.”
Since Fordice started building mats in 1992, the company has fulfilled 17 contracts in St. Francisville and has cast a total of 7 million mats at all three corps facilities. Mats cast in St. Francisville are solely for the New Orleans district, Barr said.
“The corps also has two other casting fields, one just north of Memphis, (Tenn.), at Richardson’s Landing and one in Delta, La., just across the river from Vicksburg,” Barr said. “St. Francisville is the largest, with roughly 300,000 squares on hand and a capacity of 375,000.”
That’s a drop in the bucket compared to what production was when St. Francisville opened in 1961. After the Mississippi River flood of 1983, the facility reached its highest production rate of 450,000 mats. Under the current contract, the yard produces 70,000 to 80,000 mats per year.
“It used to be we would start casting in April and it ran into December,” said Barr, who has worked at the facility since 1982. “This was almost a full-time job for the guys who worked here. Now we only have these guys a couple months, and the rest of the year they are on dredge jobs, or levee and revetment jobs.”
Since 1885, Corps engineers have been protecting the Mississippi River banks and levees with some type of revetment, Rawson said. Originally, engineers used fish pole mats, followed by willow tree framed mats, board mats, asphalt, concrete block and today’s standard articulated mats.
“Many of the original fish pole and willow mats can still be found and seen on high resolution surveys of the bottom of the river,” Rawson said.
During the 1970s and 1980s, there were five casting yards or fields on the river and two mat-sinking barges in operation. As the construction program nears completion, only three yards and one sinking unit remain.
“We only cast for three months out of the year now,” Rawson said.
Since about 1,000 miles of mat has been placed from Cairo, Ill., to Head of Passes at the mouth of the river, demand has declined dramatically.
“We survey the river every year and look for scouring,” Rawson said. Much of what is produced is for maintenance.
The corps has held celebrations at every millionth cast mark for as long as Barr can remember. This one, however, was bittersweet since many in attendance won’t live to see the 12 millionth mat. “Actually, the first inspectors from 1961 have all passed away,” Barr said.
His uncle, Joe Barr, 89, started at the yard in 1964, and was the eldest of the bunch in attendance at the recent event. The youngest was 79.
“It took us from 1999 to 2008 to cast one million mats because the demand was so low,” Barr said. “Before 1999, when we were running 350,000 to 450,000 mats a year, it didn’t take more than 2 1/2 years before we would catch another million. If we keep this current revetment season going, it will take 10 or 12 years before we make another million. I think this is real special because we may not be seeing these guys the next time around.”
Since 1961, the ACMs themselves have changed little, Barr said. However, since equipment like Fordice’s was introduced, the process requires less manual labor. “In the past, they had to do everything by hand, even pick up the forms by hand and stack them,” Barr said.
Fordice used to run a crew of 160 or 170, and now runs 75 or 80. Before demand declined, the contractor used to work a double crew, setting and casting at the same time. Today, the crew sets forms in the morning and casts in the evening.
“When I first went out there in 1982, I used to tease all those old people about having gray hairs and stuff,” Barr said. “They would always tell me, just wait, and if you live long enough you’ll see,” said the gray-haired man.
