The latest phase of Northeast Mixmaster construction in Des Moines, Iowa, is going as planned, as crews perform grading and paving of the outside lanes of I-80 westbound. The expansion of Interstate 80 from Altoona to the Northeast Mixmaster is needed to address the increased traffic volumes and to make the corridor safer for drivers.
"This phase of the project was let in August of 2024," said Scott Nixon, Iowa Department of Transportation (Iowa DOT) District 1 construction engineer. "Work began the following month to prepare for the traffic shifts needed in early 2025. The bridge subcontractor, Herberger Construction from Indianola, Iowa, also worked on bridge substructure through the winter of 2024-2025."
Iowa DOT District 1 photo
The Northeast Mixmaster is a continuation of reconstruction that began back in 2008. The current project was completed in November. The next phase, which involves the reconstruction of the eastbound lanes, will start in spring 2026. The remainder of the westbound lanes and median will be reconstructed beginning in 2027, with final completion of the corridor expected before the end of the year.
For the current phase, a number of activities had to take place in order to build new bridges at NE 29th Street, NE 38th Street and over Fourmile Creek. The 38th Street Bridge over I-80 was demolished to allow grading of the new outside lanes on I-80. The outside rail and a portion of the deck was removed on both the 29th Street and the Fourmile Creek bridges to allow a portion of the new bridges to be constructed adjacent to the existing bridges.
"The demolition of the 29th Street Bridge was restricted to the outside rail and a narrow portion of the deck," said Nixon. "Traffic is still using a portion of the existing 29th Street bridge. A temporary retaining wall is required to be constructed, due to the new bridge being much shorter than the existing one.
"The existing bridge is a four-span bridge, spanning 29th Street and an abandoned railroad. The new bridge is a three-span bridge. The temporary retaining wall is needed to accommodate the grade for the new outside lanes."
Demolition of the 38th Street Bridge over I-80 was completed in April, to allow grading to be completed for the additional lanes on I-80. The work required two nights of full closure in each direction. The contractor used multiple Komatsu track excavators to remove the bridge.
Iowa DOT District 1 photo
To remove the 38th Street Bridge, workers closed the lanes below and placed crane mats to protect the existing lanes from damage. Crews used two Komatsu track excavators to remove the bridge rails and the decks. One excavator featured a hydraulic hammer attachment, while the other included a hydraulic pulverizer attachment to help break the concrete deck, rails and beams into manageable material for removal and transporting off the job site.
Traffic on 38th Street is detoured until completion. Nixon noted that commuters quickly adjusted to the disruption.
"The closure of 38th Street over I-80 has affected the local residents who live on either side of the corridor. The detour is approximately one mile to the west, and motorists have adapted to the change with little to no problems.
"The 38th Street Bridge is just a very small portion of this project and carries the least amount of traffic out of all the roadways and structures being replaced. Because of the restricted width on I-80, and the need to maintain three lanes in each direction during construction, the new pier for the 38th Street Bridge, [located in-between the eastbound and westbound lanes and incorporated into the median barrier rail] cannot be constructed until year three.
"If we get eastbound traffic switched onto the newly constructed eastbound lanes in late 2026, the contractor may be able to start the pier work in the late fall/winter of 2026/2027 and finish the structure in 2027."
The current phase of the project, which focuses on grading and paving the outside lanes of I-80 westbound, totals $20 million. The previous phases, which included the EB I-35/80 to NB I-35 flyover ramp, and reconstructed ramps from EB I-35/80 to SB I-235 and WB I-80 to NB I-35, cost $88 million.
There have been several projects in and around the Northeast Mixmaster since work first began, in an effort to improve the safety of the interchange, as well as the traffic flow. The first phases were primarily tied to the expansion of I-235, which is the south leg of the interchange. Due to the changes made in that corridor, there were others needed within the interchange to transition to the original configuration of I-35 to the north.
The prime contractor, Manatt's Inc. of Brooklyn, Iowa, is performing the Portland cement concrete (PCC) paving on the project.
"A big challenge on this project is the condition of the existing pavement and maintaining the existing pavement during construction," said Nixon. "The existing pavement has deteriorated and needs to be replaced. Three lanes of traffic were shifted to the inside, so that work can be accomplished on the new outside lanes.
Iowa DOT District 1 photo
"The left lane of the westbound traffic was shifted next to the median barrier rail and is traveling on the old inside shoulder. The underlying pavement in the shoulder and the travel lanes has deteriorated, and the surface has required constant maintenance throughout the project. We have performed surface patching and HMA overlays to try to patch the areas and reduce the need for continual maintenance of filling potholes and deteriorated joints."
Tasks already completed include most of the median storm sewer pipe extensions and grading of outside lanes. The contractor will perform the final grading of the subgrade and will soon start placing subbase material and preparing to start paving new lanes. The bridge subcontractor is ready to pour the deck on the bridge over Fourmile Creek and also is working on substructure on the bridge over 29th Street.
Reconstructing/adding lanes to allow for four eastbound and four westbound lanes between the Northeast Mixmaster and U.S. 65 means shifting the current three lanes of traffic to inside, to accommodate building the new lanes. The work calls for additional grading on the outside of the existing lanes, extension of all the median drainage outlets and drainage pipes on the north side of the project, constructing a portion of the new bridges over Fourmile Creek and E. 29th Street, placing subbase materials and paving the new outside lanes.
Project site work includes grading of the new lanes on the north side of Interstate 80. Excavation work was required through the east half of the project for the new lanes and the new drainage ditch. The project consists of 154k cu. yds. of excavation, which was mostly accomplished using Caterpillar 740 off-road articulating trucks.
Iowa DOT District 1 photo
According to Nixon, a variety of heavy machinery is required for this phase of the project.
"For the grading portion, the excavation was performed by track excavators and the material was transported by Caterpillar 740 off-road articulating dump trucks. The material was then spread out with dozers and rolled in with sheepsfoot rollers pulled by John Deere tractors. The paving will be accomplished with GOMACO concrete pavers of various sizes. The bridge contractor has a pair of American cranes at each bridge location, along with track excavators."
The bridges consist of prestressed, pretensioned Portland cement concrete beams, with Portland cement concrete also used in drilled shafts, abutments, piers and deck. The pavement cross-section consists of 11.5 in. of Portland cement concrete pavement, with 6 in. of granular subbase more than 12 in. of special backfill, all over a layer of polymer grid that's placed directly on the grade.
Nixon said the weather has been an issue for workers.
"Crews are currently finishing grading and repairing erosion from all the rains we have had recently on the project. [We had] the wettest July on record in Iowa, and the contractor experienced numerous weather delays.
"Central Iowa started the construction season with a reasonable amount of rain in April and May, but from late June through the end of July we received above average amounts of rain. This greatly affected several projects within the Des Moines metro area, as well as around the state. Projects are on average three weeks behind schedule."
Nixon said he takes great pride in his involvement in the Northeast Mixmaster project.
"I encourage all my construction and materials staff to think about their roles in the same way. I tell them they are directly involved in changing the transportation system in central Iowa. The work that they do is making people's lives better and safer for several years to come." CEG
