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Concrete Said to Add 20 Years to Bridges

Monday, June 6, 2011

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Canadian researchers are touting the development of a more durable concrete that purportedly will increase the average lifespan of bridge decks by more than 20 years, compared to typical high-strength concrete.

The new material was developed by Dr. Daniel Cusson, a senior researcher at the NRC Institute for Research in Construction (NRC-IRC), reports the institute, Canada’s leading construction research and technology development agency.

The new concrete has been specially formulated to minimize shrinkage, which is typical of high-strength concrete, while maintaining its excellent mechanical properties.

NRC-IRC

The graph shows the time-dependent probability of concrete cover spalling in a typical reinforced concrete bridge deck. (NC=normal-strength concrete; HPC=typical high performance concrete; HPC-IC=high performance concrete with internal curing)

It also is said to greatly reduce cracking, which diminishes the penetration of aggressive agents like chlorides from de-icing salts. As a result, it takes considerably more time for the chlorides to reach the steel reinforcement, initiate corrosion, and induce further damage to the structure, NRC-IRC reports.

Focus on Sand

Researchers say the material’s secret is in the sand it contains. A lightweight porous shale fine aggregate replaces about a quarter of the normal sand used to make concrete.

This porous sand can hold up to 20% of its own weight of water, which serves to cure the concrete uniformly from the inside, thus preventing self-desiccation, the institute says.

The material costs about 5% more than standard high-strength concrete, while extending the life of concrete bridge decks by more than 20 years. The material would last 40 years longer than normal-strength concrete, NRC-IRC says.

The material will thus save on annual bridge maintenance, recurring repairs and associated traffic disruption, and replacement, researchers say.

Testing Underway; Project Considered

The self-curing material is being put to the test at NRC-IRC’s outdoor slab testing facility, where embedded instrumentation and periodic non-destructive testing are monitoring its mechanical performance and corrosion resistance.

This field testing is being conducted under the severe weather conditions that most Canadian bridges face: cyclic loading, exposure to de-icing salts, freeze-thaw cycles, wet-dry cycles and solar radiation.

Federal Bridge Corp.

A model shows the future North Channel and Canal Bridges in Cornwall.

The new concrete formulation is being considered for the deck construction of the Canal Bridge, which is part of the North Channel Bridge replacement project in Cornwall. The $75 million infrastructure project, from Federal Bridge Corp., is slated to start later this year.

Research partners include the City of Ottawa, Federal Bridge Corporation, National Capital Commission, Transports Québec and W.R. Grace.

For more information, contact Cusson at daniel.cusson@nrc-cnrc.gc.ca or 613-998-7361.