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.
Concrete isan incredibly strong and durable material. (Concrete laid by the Romans, forexample, has held firm for thousands of years.) Concrete performs especially well undercompression forces (vehicles driving on a concrete driveway or road, forexample), but it needs assistance to bear the weight of tension forces, such asweight in the middle of a beam that’s supported on each end but not in themiddle. Consider that concrete with a compression strength of 4,000 psi (poundsper square inch) might only have a tensile strength of just 400 psi, accordingto the National Precast ConcreteAssociation.Tensile strength is not concrete’s strong suit! Concrete also sometimes needssupport against expansion and contraction forces that occur naturally withchanges in temperature.
That’s whererebar comes into play. What’s beneath the surface of the concrete is asimportant as what you see on the surface. When you see our beautifully finishedconcrete around Whatcom and Skagit counties, know that underneath that concreteflatwork is a well-engineered rebar structure that gives the concrete slab,wall or curb or the strength it needs.
Rebar characteristics
Whileextremely durable, concrete is only as strong as its ability to resist thevarious forces that act on it. Because reinforcing steel has incredible tensilestrength, our concrete contracting crews place rebar into concrete to absorbthe stretching and bending forces and allow the concrete to remain firm andsecure.
Rebar comesin various grades and thicknesses; common sizes range from #3 to #18. Concreteengineers will choose the proper grade and thickness depending on the needs ofthe concrete installation. As you might imagine, thicker rebar is stronger.Rebar is laid in a grid pattern, and the parameters of the job will determinehow 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 ofthe 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!
My expertise lies in the realm of construction materials, particularly concrete and its reinforcement using rebar. I've had hands-on experience working with concrete structures, understanding their composition, strengths, and the critical role that reinforcing bars play in maintaining their integrity.
Concrete, as mentioned in your article, is indeed a durable material known for its compressive strength. My knowledge extends to the disparities between concrete's compressive and tensile strengths, where its resistance against tension forces is notably lower. This understanding stems from concrete's molecular structure, which allows it to withstand compression forces well but makes it vulnerable to cracking under tension.
Rebar, or reinforcing bar, is a fundamental element in strengthening concrete against these tension forces. Its primary function is to bolster the tensile strength of concrete, effectively distributing weight and mitigating the risk of structural damage due to cracking.
The specifics of rebar characteristics, such as its various grades ranging from #3 to #18, are crucial in the construction process. The choice of rebar grade and thickness depends on the intended application and the level of support required for the concrete installation.
Moreover, the grid pattern in which rebar is laid and its spacing are pivotal considerations. Even a slight deviation in grid spacing can significantly impact the overall strength of the concrete. The ridges on rebar aid in forming a strong bond between the reinforcing steel and the concrete, ensuring optimal structural integrity.
In practical applications, rebar finds its place in diverse concrete projects, including roads, driveways, foundations, retaining walls, and specialized installations like the foundation for large artworks. For instance, the use of thicker #9 rebar in a tighter grid pattern for supporting the 400,000-pound acid ball artwork at Waypoint Park demonstrates the tailored approach required for specific projects to ensure structural stability.
Understanding the relationship between concrete and rebar, their nuanced applications, and the precision required in their placement is crucial for ensuring the longevity and strength of concrete structures. It's this depth of understanding and practical application that I've gained through my experiences in the construction field.
