Every building material has its strengths and weaknesses. For example, try setting a wood two-by-four on two blocks about 4 feet apart. When the wood is set on its long side, it bows and flexes easily under weight. On its short side, however, the wood provides much stronger resistance.
Concrete is much the same way. Concrete is great at resisting compression, such as the weight of heavy vehicles over load points, but it is not so great resisting tensile forces that flex and pull on the material.
Consider a concrete bridge. While tons of heavy vehicles can travel the bridge without compressing the concrete, all that weight puts pressure on the underside of the bridge between the supports, which naturally wants to flex, like the two-by-four.
This is why steel rebar is so important in concrete construction. Rebar is excellent at resisting tensile forces, so it combines with concrete to create an ideal construction material — one that is easily moldable into just about any shape and that resists both compression and tension forces.
In an entertaining and informative example, Practical Engineering showed that unreinforced concrete’s resistance to tensile (pulling) forces was less than 10% its resistance to compression forces. Rebar is added to strengthen the concrete against tensile forces.
As demonstrated in the Practical Engineering video, rebar also helps to slow down the failure of concrete. With unreinforced concrete, there would be no warning that a failure was imminent. As soon as a crack forms, the entire structure is in danger of collapsing under stress, since there’s no secondary material to prevent the crack from spreading. Through its reinforcement characteristics, rebar helps mitigate that issue.
That makes rebar a necessary component of concrete bridges, foundation walls, driveways and stairs. In concrete step construction, rebar helps to hold the entire structure together while minimizing failure caused by ground vibrations and settling, which also produce tensile forces in concrete. On the Bellingham waterfront, Custom Concrete used #9 rebar, which is 1 1/8 inches in diameter, to reinforce the thick concrete foundation for the 200-ton steel Waypoint sculpture.
Concrete is a wonderful material that has many practical uses. Steel reinforcing bar, or rebar, expands on those by adding tensile resistance. Custom Concrete Contracting’s crews are concrete and rebar experts in Whatcom and Skagit counties. For help on your next project, reach out to us today.