Why Concrete Needs Reinforcement

It's the jorts (2:39), the New Balance shoes, and the pasty, white legs of one Grady Hillhouse that really endear this video to me.

Yes, Grady's style is a little dry, but he does a marvelous job showing very basic concepts of engineering as they apply to our everyday world and not just talking about the concepts but rather by building and showing small, graspable demonstrations.

In this video, Grady shows...

• how much force it takes to break two 'identical' concrete cylinders - one under tension, one under compression
• concrete beams (fairly thick beams) tested to failure with a four-point break test - a beam with no reinforcement, with 'rebar' reinforcement, and with pre-stressed 'rebar' 

Cement Reinforce with Steel Bar for Super Gas Rig Supporting Structure

Flexible concrete - an obvious oxymoron, right?

The video opens with an historical background to the improvements on concrete as well as a base recipe for making concrete - 3 parts aggregate, 2 parts sand, 1 part cement. That's a wonderful mixture for a great material - in (repeat after me) compression.

That's not a mixture for a great support structure for a North Sea oil rig that needs to have enough give to flex with the waves.

Add a few reinforcing bars, though, and the concrete becomes a radically different product.

Steel - great under tension...concrete - great under compression...reinforced steel - the dog's nuts.

British accents - also brilliant all around. Only they can give you that kind of...science.

(Warning, the linked videos there - the Brainiac video - show bad science, faked demonstrations, they should be watched only to show what doesn't really happen unless you lie to your audience. Here's my evidence.)

Concrete Countertops: How reinforcing works

Concrete is great under compression but not nearly as good under tension.

A concrete beam would make a lousy support for hanging structures.

Here the president of the Concrete Countertop Institute (really? is there an industry group for every possible subindustry?) uses a Simpsons still to help us understand the issues that exist with a concrete 'beam' like a countertop.

He then brings out a great illustration (at 2:30) of the tension/compression forces that occur on a beam when the beam bends and goes on to explain where the different tension issues occur when a beam is supported on the ends or cantilevered away from the support.

The video is a little long (nearly 10:00 in total length) but does a very good job explaining how and why reinforcement measures have to be used in concrete countertops.

If only it came with a great medallion like this one.

By the way, is that guy to the right in the picture the same one speaking throughout the video?