April 24, 2011
“Reduce, reuse, recycle,” was more than an Earth Day statement to the Missouri Department of Transportation (MoDOT) — it’s one way the department continues to keep construction environmentally friendly and save money.
Though it may seem somewhat ironic for a process that, by its very nature, must tear down existing landmarks to construct new ones, the department makes significant efforts to minimize the impact its construction has on the environment.
An example of MoDOT’s “green” commitment is the Route 141 reconstruction project in west St. Louis County. This project relocates a section of Route 141 slightly to the east of its current location and raises the roadway out of the floodplain. The eventual roadway will also reduce congestion along the route and will improve the roadway’s safety.
“As we were evaluating and designing the Route 141 project, one of the biggest concerns the public presented to us was preserving the environment,” said Karen Yeomans, MoDOT area engineer for west St. Louis County.
To reduce the number of trees removed for the project, for instance, the design team evaluated the entire area and established protection zones — the construction contractor would be penalized if they removed or damaged trees in those zones.
“Since, we are relocating Route 141 onto an area that was mainly forested wetlands, many people were concerned about our potential impacts — we evaluated all of them carefully during the planning and design process. We met all the federal and local requirements for wetland and forest preservation, but also wanted to make sure this project was a model for environmentally friendly construction for the region,” she said.
Often, construction projects are entirely cleared between right of way lines — MoDOT wanted to only take the trees needed to safely build the roadway and keep it safe for drivers.
“We understand that it takes 40 years to replace a 40-year-old tree, and we wanted to save every one that we could. We also made sure, though, that we wouldn’t have trees too close to the road that could fall and endanger drivers,” said Yeomans.
The construction contractor also incorporated an idling policy — that no construction vehicles could be idling for extended periods of time, reducing the fuel used on the project and the pollutants from those vehicles.
In addition, the project uses wicking drains, instead of pumps, to help remove water from the ground — these drains absorb the ground water and bring them to the surface naturally.
Much of the material that is on property is reused or recycled — for instance, the trees that were removed were made into mulch and used for erosion control. Concrete from Olive Boulevard and Ladue Road will be used for the new roadway base or for fill.
“We also reuse as much of the earth we excavate on the project as we can. This helps eliminate the need for hauling the earth off the project, which also reduces the need for trucking,” said Yeomans.
The department is also testing new technologies to make the project more environmentally friendly. Last summer, for instance, MoDOT tested a process to place concrete. This process, called two-lift paving, lays down a thick layer of concrete and then immediately places a second, thinner “lift,” or layer of concrete on top of that thick layer. Concrete placed using this method is as strong as that used on standard concrete pours.
“What this process allows us to do is place two different concrete mixtures. On the Route 141 project, this will be used to test a special concrete additive that captures pollutants and breaks them down using sunlight. This photocatalytic, or ‘smog-eating’ concrete additive is expensive, so being able to place a large concrete mixture base and then place a thinner layer with the additive is very important,” said Yeomans.
MoDOT will test a 2,000-foot section of the new Route 141 with this smog-eating concrete. This type of concrete has been used successfully in Europe.