Everyone knows that adding rebar to concrete makes it stronger. Usually, rebar is needed when concrete surfaces have to carry heavy loads and traffic. The rebar gives the concrete extra tensile strength and prevents the formation of cracks. But what about other concrete projects?
For some projects, reinforcing steel is not necessary or even recommended! This is true for concrete curbs. So how do concrete contractors retain the structural integrity of the curb?
How Are Concrete Curbs Constructed?
A curb is a functional and aesthetic connection between two areas of slightly different heights. They are very important to define the border between the paved surface and the walking areas, adding strength and stability to the pavement by creating a rigid borderline structure along the edge.
Curbing does more than define a concrete area – it strengthens it, too! Curbs confine flexible pavement and improve sub-base compaction. While they are necessary for street and residential projects, curbs don’t have the same uses as other forms of concrete construction. They don’t carry the same consistent loads as a driveway or walkway (at least, if everyone in your neighbourhood is a good driver!).
This means that including rebar or other types of reinforcing steel doesn’t do much to improve curbing; rather, it makes the construction of these elements more difficult and increases the final cost of the project. We have other ways of making sure that concrete curbs stay strong: jointing!
How Concrete Curbs Use Jointing
Even though curbs do not face everyday forces other concrete surfaces experience, this doesn’t mean they don’t crack or weaken over time. Curbs will experience shrinkage due to temperature or moisture changes, and they can crack when these factors exceed the tensile strength of the concrete. To compensate for this expansion and shrinkage, we use concrete joints instead of rebar.
When a curb is constructed as part of or tied to the pavement, the workers should carry the jointing pattern for the pavement through the curb. These pre-planned cracks are called “contraction joints,” and we place them at intervals close enough to prevent intermediate cracks from forming; these intervals are usually about 15 feet apart. This spacing could be different based on local factors.
Contraction joints should be cut at a depth about one-fourth that of the cross-section of the concrete. We can cut them with a saw, form the joints with thin steel dividers or impress tee-bars shaped to match the cross-section of the curb and gutter. If sawing is the solution, we must do it as soon as possible so that we can form the joints before cracks can set in. If we’re using division plates, they have to be placed in the forms and then removed once the concrete has set.
We use rebar to provide the right level of tensile strength for many of our concrete projects, but sometimes, it can be too much. For concrete curbs, the right solution for both structural integrity and the bottom line is contraction joints!