IMEG staffers do whatever it takes for Mississippi River bridge project
For over a year now, IMEG has been providing construction engineering and inspection services for the $1.4 billion Interstate 74 Bridge Corridor Project that will culminate in 2020 with the opening of a new bridge spanning the Mississippi River between Moline, Ill., and Bettendorf, Iowa. To date, IMEG staff have spent over 11,000 man-hours on the project.
IMEG teams have been engaged in construction observation, verification, documentation, and inspection of various parts of the project in all types of weather, day and night, on land and, for some, on barges in the middle of the river. All teams have had their share of challenges – including the group led by IMEG Construction Services Manager Eric McLaughlin, materials testing task manager for the Iowa DOT’s portion of the project. He shares what his team has experienced over the past 12-plus months in the following Q & A.
Q. What has it been like to work on this project?
A. In the past year there have been only two or three weeks (last winter) when we were not on a concrete pour. We are out in the middle of the river in any condition you can think of – rain, snow, sleet – at every hour of the day. It has been really challenging, but we have a fantastic group of people who have stepped up and have done everything we have asked them to do. We are currently involved with four separate projects and four contractors – and it’s been a challenge to make sure we’re in the right place at the right time.
Q. How much time does it take to test a concrete pour?
A. Our testing has ranged from small, hour-long, three- to five-cubic-yard pours on land to pours lasting up to 30 hours – the biggest to date being a 2,500-cubic-yard pour on the river.
Q. What does concrete testing involve?
A. Concrete can only be delivered on the river by barge, four trucks at a time. We take a sample from one of the trucks as it arrives and test the concrete to ensure it meets Iowa DOT standards before it can be placed into the forms. We do that for every round of barges. We track the concrete’s temperature, air content, slump, water added, and witness the spread and J-ring test. There’s also a time limit on concrete – you only get two hours from the time water hits cement at the plant until the resulting concrete must be rejected. So, we keep track of when each truck is batched, when it starts dumping, and when it finishes dumping. We also do the destructive testing (cylinder or beam breaks), in which samples of concrete are taken back to the lab and broken.
Q. How many staffers are involved in a pour?
A. A typical day is one to two people per pour, with two to three pours per day. Another person performs plant monitoring at one of four different concrete plants we cover. On a bridge deck pour we’ll have five to six people – four or five on site to perform the on-deck testing and sampling, and one at the concrete plant. Sometimes we borrow staffers from our survey team, depending on the size of the pour and number of shifts. Duties on the barge include grabbing samples with buckets – from the concrete trucks and at the point of placement at random intervals – to perform the on-site testing. In addition, one person recalculates the water/cement ratio if water is added, tracks concrete times and temperatures, and logs the test data. I work in the office, full-time, uploading our field data to the Iowa DOT, and assist on the big pours.
Q. What happens if a batch of concrete is rejected?
A. The truck sits on the barge until it’s time to go back to land.
Q. What kind of hours does the team put in?
A. We’re working 8 to 10 hours most days now, but once or twice a week we’ll have a 12- to 18-hour day. At least two times a month we’ll have a big pour on the river that goes 20-plus hours. A recent pier 12 eastbound footing pour lasted 25 hours (including multiple rain storms) and required two shifts. We’ve had at least 10 pours of that size, with probably another 10 to go.
Q. What about the weather?
A. We work in all conditions – in January we were testing drill shaft concrete when it was 30 degrees and the wind was blowing 20 miles per hour out on the river where there is no shelter. We have a talented, selfless staff who understand that this project needs our time and are willing to work on it in all kinds of weather.
Q. Speaking of the barge, what about the “accommodations?”
A. When you’re out there, you take everything you need with you because you cannot go back to land. We bring our lunches and we have a small blue canopy for shelter. There are porta-potties, and the contractor offers bottles of water. On a giant pour, the contractor or concrete company will bring pizza out around dinner time.
Q. Do you ever stop to contemplate this unique work environment?
A. You kind of forget sometimes that you are standing on steel pontoons in the middle of the Mississippi River in a downpour at 1 in the morning. You step back every now and then and realize, “Hey, this is crazy.”
Q. Aside from the long hours, extreme weather, and isolation on the river, are there any other challenges?
A. The self-consolidating concrete (SCC) being used on the project is new here and newer to the Iowa DOT. It’s being used on all pier stems and the main arch pedestal structures in the river due to its ability to flow around rebar and its high strengths. The arch pours are mass concrete, which also has very stringent temperature requirements, so the concrete producer is using liquid nitrogen to cool the concrete, another first for our area. The liquid nitrogen just adds to what makes SCC a totally different animal from conventional concrete. The mix is finicky and probably takes one-and-a-half times as long to pour.
Q. When you drive across the finished bridge in 2020, what do you think will go through your mind?
A. Although we are not building the bridge, when we drive over the finished product we’ll know we were a major part of it and
were involved since the first drop of concrete was placed – every drilled shaft poured in the river, every footing on land, every pier, every pier cap, every bridge deck pour. It’s kind of humbling.
For survey team, it’s all about accuracy and coordination
Standing atop 2-inch rebar inside successive drilled shaft cans spanning the river, the pair “leapfrogged” to the project midpoint, taking measurements along the way while the survey firm working the Iowa side did the same. The vertical discrepancy amounted to less than an inch; both firms made adjustments so that each side of the bridge would meet at the proper elevation. “We were there at 4:30 a.m. and didn’t leave the river until about 8 at night,” said Misfeldt. “We had to get it done so that it didn’t slow down the contractor.”