Category Archives: Bridges and Structures

New Project: Bridge Low Slump Concrete Overlay Mix Design for Mobile Mixers

In recent years, MnDOT has seen an increase in cracking of low slump overlays. Cracking of overlays allows chlorides to get into the bridge deck which leads to deterioration of the reinforcement and eventual delamination or spalling.  This means that the bridge deck needs to be repaired or even replaced before the service life has been reached. 

What is a low slump overlay? A low slump overlay is a technique used by DOTs to extend the life of bridge decks. They are typically 2″ thick and designed to provide low permeability.

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Monitoring System Provides Decade of Data From I-35W Bridge

This article was originally published in Catalyst, August 2020.

On August 1, 2007, the I-35W Saint Anthony Falls Bridge collapsed in Minneapolis. Its replacement, open to traffic just over a year later, was instrumented with more than 500 sensors to record the new structure’s behavior and evaluate the effectiveness of different monitoring strategies. A 10-year review of the bridge’s monitoring system is now available from U of M researchers.

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GFRP Rebar Shows Promise for Use in Bridge Decks

Reinforced concrete bridges are built to handle heavy loads and routine traffic for 75 years or more. But bridges in climates like Minnesota’s are exposed to moisture and chlorides from road salts that may penetrate these structures and corrode the steel.

In a recently completed research project, funded by MnDOT and the Local Road Research Board, researchers studied a rural bridge built in 2017 near Elgin, MN, that used glass fiber–reinforced polymer (GFRP) rebar in the bridge deck. They found that GFRP performed well, proving sufficiently strong for use as an alternative to corrosion-susceptible steel rebar.

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Methods to Mitigate Bridge Corrosion Show Mixed Results 20 Years Later

Well-documented efforts undertaken two decades ago to mitigate corrosion of a Highway 394 reinforced concrete bridge have given researchers the perfect scenario for evaluating the treatments’ long-term effectiveness. The test results are mixed: State-of-the-art methods for electrochemical chloride extraction and fiber-reinforced polymer wrapping of bridge elements performed well in combination, but poorly in isolation.

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Putting Research Into Practice: New Tool Estimates Bridge Construction Time

A new spreadsheet tool developed by the Minnesota Department of Transportation draws on historical data to help project engineers better estimate bridge construction time. The method allows users to project time-frames based on bridge design elements, work scheduling and other inputs, utilizing estimates from comparable projects in a 10-year database of bridge-building data.

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Using Debonded Strands to Reduce End Stress in Bridge Beams

A new MnDOT-funded research study has found that most agencies in states with weather similar to Minnesota’s use debonded strands in prestressed concrete bridge beams. MnDOT may begin piloting debonding as an alternative to draping, which manufacturers claim is time-consuming, challenging to worker safety and expensive.

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Study Underway to Harness Renewable Energy from Minnesota’s Highways

Sound barriers and snow fences along highways have the potential to provide clean energy in Minnesota.

A newly funded MnDOT study, Harnessing Solar Energy through Noise Barriers and Structural Snow Fencing, is investigating how to utilize existing noise barriers and snow fences on Minnesota highways to harvest clean, cost-effective energy.

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