The Minnesota Department of Transportation has a new way to more uniformly estimate steel rebar corrosion in concrete bridges. Engineers found that a 3D scanning method could accurately estimate section loss when the loss is greater than 75%, though not for smaller losses.



Corrosion of steel reinforcement in bridge structures creates uncertainty in the structural capacity. A new prediction tool will help estimate rebar section loss to accurately plan for appropriate bridge maintenance repairs.

While bridges are generally designed for at least a 75-year life span, damage from corrosion can manifest after a few years of exposure. Fluctuations in temperature and moisture, and exposure to deicing salts may cause material deterioration such as corrosion of steel rebars embedded in concrete bridge structures.

Corrosion of rebar creates rust and rebar cross-section loss—a weakening of and decrease in steel content. Because rust has a higher volume than the steel rebar, the rusting process also causes expansion that results in concrete cracking and potentially spalling. Whether the rebar is still providing structural reinforcement at design capacity depends on how much of the steel bar’s cross-sectional area remains intact.

“We’ve developed and calibrated a set of models with Minnesota-specific conditions for more accurate estimates of reinforcement section loss. Such estimates are instrumental in ensuring the safety and performance of bridge structures in service,” Behrouz Shafei, associate professor, Iowa State University.

Conventionally, bridge inspectors visually assess bridge structures to look for cracks and use hammers to find delaminated concrete and visible rebar. There is, however, no industry standard to measure the section loss of the reinforcing steel rebar. While the inspector may use visual judgment or a caliper to measure the remaining diameter if the rebar is exposed, there is little guidance to assess section loss if the steel reinforcement is still within the concrete.





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