Dear PRT reader, Thank you for your question, “What is Rebar?”

In these times of war and natural disasters this is a very timely question which displays itself in everyday television news coverage. Rebar, the universal short term for “concrete reinforcing bar,” is a high tensile strength steel bar placed within cast concrete structures to add strength in tension. Rebar is round with protruding angular oriented external surface protrusions all along its length which allow the bar to be securely embedded in a concrete castings. 

Concrete, one of the world’s most widely used structural materials, has great compressive strength, but has negligible tensile strength. Rebar is used within concrete castings to overcome this fault. Picture in your mind that you have a concrete post embedded vertically in the ground before you. At the top if you were to push this post to the left, the left side of the post will experience being in compression and the right side will experience being in tension. Since concrete is incapable of resisting tension forces it will crack and fail, falling to the left. But—if you embed a piece of rebar within and along the right edge of this post, the rebar will take all the tension forces created by your push on the post. This is the basic principle of how rebar is used. Consider another couple of examples. When pouring  large slabs of concrete for a parking garage it might require hundreds of individual rebar laid down low in the floor casting. Instead of rebars, a reinforcing steel mesh, or “remesh” is laid down instead. Or, as might be in the case of stopping cracks or chunking in a concrete driveway, millions of monofilament fibers might be added to the final concrete mix and will be interspersed throughout. 

As you watch the coverage of world news take notice that in the more ‘developing world’ disaster areas. You might observe concrete and masonry debris as a simple pile of loose blocks scattered on the ground. As you observe sites more in ‘first world regions,’ the piles of destruction appear to be more like partial sheets of deformed concrete, standing pillars and columns and a significant entanglement of steel bars. Instead of having relied on mortar alone, the inclusion of rebar had greatly improved the strength of these cast structures.

I look forward to hearing more questions from PRT readers. Any questions and comments may be submitted via email directly to Responses will be given directly to the submitter or will be published in subsequent issues of the PRT in this column.