Concrete: Guaranteed to crack - but cracks can be controlled

Concrete’s strength is its strength. But that strength comes with the costs of inelasticity and shrinkage.

Through the effects of both tension and shrinkage, all concrete structures will eventually crack—whether the concrete has sufficient compressive strength or not. Concrete’s natural process of transforming from its plastic state to solid creates shrinkage.

In addition to concrete’s inherent characteristic of shrinking about 1/16 inch for every 10 linear feet, temperature may cause some expansion and contraction. Add the variable of environmental moisture changes, and a solid expanse of poured concrete for a floor or slab is practically guaranteed to crack!

That’s why a conscientious Structural Engineer includes control joints in his specifications. Control joints direct the cracks caused by concrete shrinkage to occur within the joints, therefore minimizing the occurrence of random, unattractive cracks and creating a gap opening around the slab’s perimeter.

When you see a crack-free expanse of concrete, you see an engineer’s well-designed work.

Sometimes, however, cracks do occur.

Cracks caused by shrinkage are not normally a structural defect, but may still require sealing to protect against the entry of water or radon gas into the building. When any concrete cracks, it creates the possible entry for water to leak into the building. Polyurethane foam sealant is effective for preventing water entry at foundation cracks, but it is also important that the outside source of the water is identified and corrected at the same time. Epoxy, sealant, or a masonry patch compound is an effective repair material, applied after chipping out the crack.

Before repairing a foundation crack or a ¼” or larger crack in a poured concrete wall, one must assess the effects on the building and identify what caused the crack. Could there be an underlying problem that is causing foundation movement or damage? A Structural Engineer’s evaluation will take into consideration the crack’s size, pattern, location, impact on the building as well as its cause.

When a foundation crack is not traced to building movement, structural or site problems or other conditions requiring site or structural repairs, the “fix” can be as simple as a masonry repair epoxy or sealant.

Remember that shrinkage in poured concrete walls or floor slabs is a normal property of curing concrete. When it comes to concrete, however, there is no such thing as economical deferred maintenance.

Call me at 627-6873 or send an email to tom@zugassociates.com to discuss any specific concerns that you may have about the concrete in your building or project.