Tag Archives: bridge decks

Using History to Predict Bridge Deck Deterioration

Just how long will it be before a bridge deck needs to be rehabilitated?  Why not look to history to find out?

Researchers have put several decades of MnDOT bridge inspection records to good use by analyzing old bridge deck condition reports to calculate how quickly similar bridge decks will deteriorate.

MnDOT inspects bridges regularly, but had never used this historical data to help determine the rate of bridge deck deterioration and what factors influence it.

“We’re always trying to improve the timing of bridge deck repair projects and improve our understanding of what contributors affect the way our bridge decks deteriorate,” said Dustin Thomas, MnDOT’s South Region Bridge Construction Engineer.

Data-Crunching

From their analysis, researchers created deterioration tables that can be used to better predict the timing and costs of repairs and maintenance.

Researchers looked at the inspection history and construction details of 2,601 bridges to determine the impact of factors such as type of deck reinforcement, depth of reinforcement below the driving surface, traffic levels and bridge location.

Using the inspection data, researchers developed curves that show how long a bridge deck is likely to stay at a given condition before dropping to the next. They developed separate curves for each variable that had a significant impact on deck deterioration rates.

What They Found

Several factors were found to have a notable impact on how quickly bridge decks deteriorate:

  • Decks without epoxy-coated bars built between 1975 and 1989 deteriorate more quickly than other bridge decks.
  • Bridges with less traffic showed slightly slower rates of deterioration than highly traveled bridges.
  • Metro area bridges drop to a condition code of 7 (good) more quickly than bridges in other parts of the state. This may be due to increased chemical deicer usage or because maintenance activities like crack-sealing are more likely to be delayed on larger metro bridges  because of the difficulty accessing middle lanes.
  • When a new deck is installed on an existing bridge, the deck performs like a brand-new bridge and so MnDOT should use the deterioration table for the re-decking year, rather than the year the bridge was originally constructed.

MnDOT plans to incorporate future bridge inspections into the dataset to enhance the predictive value of the deterioration tables.

Related Resources

The impact of overlays on bridge deck deterioration in Minnesota was not clear, but redecked bridges were found to perform similarly as brand-new decks.

‘High Bridge’ study yields insights on bridge deck maintenance

One of St. Paul’s most iconic landmarks is helping the Minnesota Department of Transportation find the most cost-effective methods of maintaining concrete bridge decks.

For the last three years, the Smith Avenue High Bridge, which connects downtown St. Paul with the city’s west side, has served as a test bed for a variety of products used to seal cracks on bridge decks. Through MnDOT-funded research, various sealant products have been applied on different areas of the bridge deck, with their performance tracked over time.

“This project will help MnDOT make cost-effective maintenance decisions to preserve its current bridge infrastructure,” said Sarah Sondag, a senior engineer with MnDOT Bridge Operations Support.

The bridge was chosen in part because of its large deck area, which allowed for the application of 12 sealant products and three control sections.

Sealing deck cracks is a routine preventive maintenance task for bridge crews. Left untreated, cracks can allow moisture and chlorides to penetrate the bridge deck, which can lead to the corrosion of reinforcing steel, deck deterioration and the need for early deck replacement.

researcher testing permeability of a deck crack on the Smith Avenue Bridge
A researcher tests the permeability of a crack on the deck of the Smith Avenue High Bridge in St. Paul.

MnDOT maintains a list of approved bridge deck crack sealing products, but until now had little data on how well each one performs in the field. The recently published report also examined several products that are not currently on the Approved Products List.

Among the study’s findings: some of the products on MnDOT’s Approved Products List did not perform as well as other products that are not currently on the list. MnDOT is using the results of the study to update its qualification process for products to get on the approved list. Insights gained from studying application techniques will also be used to update MnDOT’s bridge maintenance manual.

*Note: This blog post was adapted from an article and technical summary that will be featured in the upcoming issue of the Accelerator newsletter.

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