Wondering what concrete shrinkage cracks are? If so, this short article has what you need. We’re going to cover what concrete shrinkage cracks are, what causes them, what they look like, and more.
What Are Concrete Shrinkage Cracks?
Concrete shrinkage cracks are non-structural cracks in poured concrete. They’re very common. In fact, you should even expect them. However, because they’re non-structural crack, they don’t affect the concrete’s ability to do what it’s supposed to do. In other words, they’re just ugly. Concrete shrinkage cracks are usually not even repaired.
What Causes Concrete Shrinkage Cracks?
Concrete shrinkage cracks are caused by shrinkage during the concrete drying process.
Concrete is a porous substance and acts something like a sponge. When concrete soaks up water, it expands. When concrete dries out, it shrinks like a sponge shrinks when it loses moisture. Freshly poured concrete is 20-25% water. When it dries, shrinkage cracks form within a few hours of pouring the concrete. They’re often called “plastic shrinkage cracks” because the concrete isn’t hard when the cracks appear.
Here’s how concrete shrinkage cracks happen…
Concrete shrinkage cracks happen because the surface of the concrete dries faster – and shrinks – because it’s exposed to air. The concrete not on the surface dries more slowly and, therefore, doesn’t shrink at the same rate as the surface. These two different shrinkage rates create tension, and concrete shrinkage cracks develop.
Although there are ways to reduce the chance of shrinkage cracks, eliminating them is next to impossible. They’re always going to happen. They’re a fact of concrete life.
So, concrete shrinkage cracks form because the surface of the concrete dries faster. This means concrete shrinkage cracks are more likely to happen when…
For more information about concrete cracks, see Types of Cracks in Concrete Slabs.
What Do Shrinkage Cracks Look Like?
Concrete shrinkage cracks are hairline and barely visible. If you see another kind of crack, it probably wasn’t caused by shrinkage.
For more information about cracks in concrete, see, How to Repair Large Cracks in A Concrete Garage Floor.
What Shrinkage Cracks Don’t Look Like
Concrete shrinkage cracks will not be…
If the crack is caused by concrete shrinkage, one side of the crack will not be higher than the other. Cracks that are vertically displaced are usually caused by differential settlement. See the graphic below.
If you see a crack without breaks, it probably wasn’t caused by concrete shrinkage. Concrete shrinkage cracks are meandering and discontinuous.
Accompanied by corrosion
Cracks accompanied by corrosion were probably caused by rusted rebar. You won’t see any corrosion on the slab’s surface with concrete shrinkage cracks.
Wider than hairline
If the crack is wider than hairline – that is, if you can fit a coin into it – it’s almost certainly not a concrete shrinkage crack but something more serious.
Why Does Concrete Crack? – Other Types Of Cracks In Concrete Slabs
Concrete shrinkage cracks are just one type of crack. Concrete slabs such as sidewalks, driveways, and pool decks can crack for other reasons, including:
While concrete shrinkage cracks may look ugly, they don’t generally affect how the concrete functions. Concrete cracks larger than hairline probably weren’t caused by shrinkage. If you see any larger cracks, they need to be looked at by a professional.
Check out our complete guide to foundation cracks.
If you’re concerned about concrete cracks and are in our service area – Hampton Roads and the surrounding area – contact us today for an inspection and repair estimate.