The wonderful world of re-bar

>> The lowdown on all those concrete-encased steel rods

By PHILIP PREVILLE

These days, it seems everywhere you turn in Montreal you find another construction site. Which means you also see dozens of those enigmatic steel rods, either springing from demolition rubble in twisted and grotesque forms or rising straight from newly poured concrete like the spouts of a fountain.

It's called re-bar. And though it may seem innocuous, it is, along with concrete, quite literally one of the pillars of urban life.

The name: Re-bar is short for "reinforcement bar" because it is used to reinforce the concrete foundations of a structure. Some say it's also short for "recycled bar" because it is made, by and large, from recycled cars. The plural form of re-bar is "re-bar," just as the plural of sugar is "sugar." Like sugar, re-bar is sold by the kilo. And like sugar to any cake, re-bar is an essential construction ingredient. A home might require 1,000 kg of re-bar, while a project like the Palais des Congrès expansion (pictured here) requires thousands of tonnes.

The purpose: Although concrete has tremendous compression strength (you can build almost anything atop a concrete foundation and it will not crumble under the load), it has low tensile strength. That is, a concrete wall does not withstand wind gusts, earth vibrations or other bending forces very well; left to its own devices, it will lilt over time. Steel-reinforced concrete solves that problem.

The cost: According to Laval-based Ferneuf, one of Montreal's largest re-bar dealers, re-bar sells for between $950 and $1,300 per tonne. The actual price depends on the quantity, thickness (anywhere from 10 to 55 millimetres), and shapes required. Depending on the structure, engineers may require re-bar of different lengths, bent into canes, squares, or L-shapes. Since construction sites do not have the equipment to bend or cut re-bar, Ferneuf always fills custom orders.

The problems: Engineers originally thought re-bar would be foolproof: because it was encased in concrete, it would never be exposed to the elements. As it turns out, concrete is more porous than anyone imagined--water continuously seeps through its fissures. Add a little salt on the roads to melt the winter snow, and suddenly salt water is seeping through the concrete, corroding the re-bar. As the steel corrodes into rust, the re-bar expands and splits the concrete open. Corroding re-bar is the main reason why Montreal's bridges are in a continuous state of disrepair.

Final factoid: Solving the re-bar corrosion problem is currently the cutting-edge of construction technology. You can get epoxy-coated re-bar, galvanized-steel re-bar, even stainless-steel re-bar. One local company, Pointe-Claire-based Solhydroc, is the region's exclusive dealer of C-BAR, or re-bar made from fibre-reinforced polymer. Solhydroc's literature claims C-BAR is "totally resistant to chloride ion attack." So much for the new steel.

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