Rebar, or reinforcing bar, is a common feature of many concrete applications. Its primary purpose is to increase the tensile strength of the concrete, helping it resist cracking and breaking. With greater tensile strength, concrete is better able to resist breaking under tension.
In a recent article about concrete control joints, we wrote about how these joints exist to help ensure that concrete cracks only in the most desirable places. After all, it’s inevitable that concrete will crack, and control joints help the concrete do so only in straight lines at the joints. Rebar holds a similar function in that the steel provides strength to a concrete structure, distributing weight with the aim that any cracking that does occur doesn’t result in structural damage.
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Concrete is an incredibly strong and durable material. (Concrete laid by the Romans, for example, has held firm for thousands of years.) Concrete performs especially well under compression forces (vehicles driving on a concrete driveway or road, for example), but it needs assistance to bear the weight of tension forces, such as weight in the middle of a beam that’s supported on each end but not in the middle. Consider that concrete with a compression strength of 4,000 psi (pounds per square inch) might only have a tensile strength of just 400 psi, according to the National Precast Concrete Association. Tensile strength is not concrete’s strong suit! Concrete also sometimes needs support against expansion and contraction forces that occur naturally with changes in temperature.
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That’s where rebar comes into play. What’s beneath the surface of the concrete is as important as what you see on the surface. When you see our beautifully finished concrete around Whatcom and Skagit counties, know that underneath that concrete flatwork is a well-engineered rebar structure that gives the concrete slab, wall or curb or the strength it needs.
Rebar characteristics
While extremely durable, concrete is only as strong as its ability to resist the various forces that act on it. Because reinforcing steel has incredible tensile strength, our concrete contracting crews place rebar into concrete to absorb the stretching and bending forces and allow the concrete to remain firm and secure.
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Rebar comes in various grades and thicknesses; common sizes range from #3 to #18. Concrete engineers will choose the proper grade and thickness depending on the needs of the concrete installation. As you might imagine, thicker rebar is stronger. Rebar is laid in a grid pattern, and the parameters of the job will determine how close the rebar is laid — how small the grids are. Spacing is critical, because grids that are off by just one inch can reduce the overall strength of the concrete by 20 percent. You’ve probably noticed the ridges in rebar; that’s to help the reinforcing steel and the concrete make a tight bond.
Rebar applications
Here at Custom Concrete, we use rebar in a number of different applications throughout Whatcom and Skagit counties. Concrete curbs, roads, driveways, slabs, foundations and retaining walls all typically need rebar of one size or another. Some concrete driveways might see rebar spaced at rather wide intervals. When we laid the foundation for the acid ball artwork at Waypoint Park in Bellingham, we used much thicker rebar in a tighter grid to help the concrete retain its integrity while supporting the enormous weight of the ball. For that job, we poured a thick concrete foundation featuring #9 rebar. We placed the rebar, which is 1 1/8 inches in diameter, in a one-foot grid with two levels. Go check out the park in Bellingham to see how Custom Concrete’s rebar and concrete installation is supporting that 400,000-pound piece of artwork!
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Category: WHY
