OTTAWA, ON — 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 the NRC Institute for Research in Construction.
Invented by Dr. Daniel Cusson, a senior researcher at the Institute, 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 -- lightweight 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, Dr. 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 non-destructive 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 Corporation is slated to start later this year.
This article originally appeared on Globe-Net, and is reprinted with permission.
Photo CC-licensed by Cliff1066.