by John Latta, Tina Grady Barbaccia and Mike Anderson

New Life Expectancy

Self-curing concrete from Canada and long-lived bridge decks

A more durable concrete that will increase the average lifespan of bridge decks by more than 20 years compared to typical high-strength concrete, and by more than 40 years compared to normal-strength concrete, has been developed by Dr. Daniel Cusson, a senior researcher at Canada’s NRC Institute for Research in Construction (NRC-IRC).

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)

 This high-performance concrete has been specially formulated to minimize shrinkage, which is typical of high-strength concrete, while maintaining its excellent mechanical properties. It also greatly reduces cracking, which diminishes the penetration of aggressive agents into the concrete, such as chlorides from the de-icing salts used on roads. 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.

The key difference is in the sand: lightweightt, porous, shale-fine aggregate, which replaces about a quarter of the normal sand used to make concrete. This porous sand can hold up to 20 percent of its own weight of water, which serves to cure the concrete uniformly from the inside, thus preventing self-desiccation. With a unit cost only 5 percent higher than that of a standard high-strength concrete, Cusson expects concrete bridge decks made with this new concrete to last longer, saving taxpayers money in annual bridge maintenance, recurring repairs and associated traffic disruption, and replacement.

Currently, this new self-curing, high-performance concrete is being put to the test at the NRC outdoor slab testing facility, where its mechanical performance and corrosion resistance are being monitored with embedded instrumentation and periodic nondestructive testing. 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.

This 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, National Capital Commission, Transports Québec and W.R. Grace.

For more information, contact Daniel Cusson at daniel.cusson

@nrc-cnrc.gc.ca or 613-998-7361.

Editor’s Note: This story and photo are reproduced from the March 2011 issue of Construction Innovation (www.nrc-cnrc.gc.ca/ci) with permission from the National Research Council of Canada Institute for Research in Construction

Innovation: Learn How it’s Done

This could change the way you do what you do.

It’s the inaugural TransOvation Workshop and Exhibition (September 6-9, Lansdowne Conference Center, in Leesburg, Virginia). Speakers will share the secrets of their “idea incubating” corporate cultures and how they have used innovative thinking to solve problems and change the way their companies do business.

And Better Roads is a media partner to the event that is the work of the American Road and Transportation Builders Association. The program was developed specifically for young industry executives and offers Professional Development Hours.

Speakers include:

• Ted Zoli, a heralded bridge engineer and a vice president at HNTB, is a 2009 MacArthur Foundation Fellowship recipient. Esquire magazine profiled Zoli in a 2010 cover story, “The Brightest: 16 Geniuses Who Give Us Hope.” Zoli also teaches at Princeton and Columbia.

• John Hillman, winner of the 2010 Engineering News-Record magazine “Award of Excellence” for his development of the Hybrid Composite Beam.

• Darcy Winslow, Nike’s sustainability innovator and executive-in-residence at MIT’s Sloan School of Management, has been called a “business rock star.” She will reveal how her team brought a sustainability revolution to Nike.