The Proper Rebar for Concrete

Types of Rebar

• Traditional carbon steel rebar is the most commonly used reinforcing bar. It is relatively inexpensive, and has been the standard for decades. However, standard steel rebar does rust and deteriorate over time, especially in harsh environments, such as marine environments and roads and bridges in Northern climes where road salt is used frequently. The chloride ion from the salt seeps into the concrete and reacts with the carbon steel rebar, weakening the rebar and therefore the concrete. In these situations, stainless steel rebar is often used. While more expensive than carbon steel, it is much less expensive than replacing deteriorated bridges.

Rebar Sizes

• Rebar is coded by numbers, such as #2, #3 and #4, all the way up to #18. The size number (numerator) can be put over eight (denominator) to make a fraction indicating the diameter of the bar. For example, #2 rebar is 2/8 inches. The American Concrete Institute Building Code suggests that for concrete cast against dirt, the minimum cover of the rebar should be three inches. Formed concrete, which is exposed to earth or water using #5 bars or smaller, need to be covered with 1 1/2 inches of concrete. For #6 through #18 bars, they need to be covered with at least two inches of concrete. Formed concrete that is not exposed to earth or weathering, such as interior walls and slabs that use large rebar between #14 and #18, need to have at least 1 1/2 inches of concrete cover, while interior slabs using #11 and smaller bars need a minimum of 3/4 inches of concrete.

Rebar Ties

• Rebar in floors, walls, mats, columns and cages is often put together in a grid pattern for extra reinforcement. To keep the rebar in place so it doesn't shift, it needs to be tied at the cross joints. There are several types of ties to use, each made with 15- or 14-gauge wire. Tie bars at every fourth or fifth intersection in most cases.

Structures

• Rebar is used in many concrete applications, including buildings, highways, bridges and driveways; however, some concrete applications do not use rebar. Notable among these is sidewalks, which usually have no rebar. One reason for this is that sidewalks do not normally bear much weight; therefore, they do not need to be reinforced. Another is that sidewalks change relatively frequently and rebar makes the demolition process much more difficult.