What Causes Concrete to Crack?

One of our most asked questions is: Why is there a crack in my concrete? Or what causes concrete to crack? Although cracks in concrete are merely just an aesthetic problem, not a workmanship problem, many do not want cracks in their freshly poured concrete. We want to address some of the causes that make concrete crack so that customers and clients can have a better understanding, as well as some of the different types of concrete cracks. 
American Concrete Institute touches on the issue of cracking concrete in their American Concrete Institute manual, ACI 302. 1-40:
“Even with the best floor designs and proper construction, it is unrealistic to expect crack-free and curl-free floors. Consequently, every owner should be advised by both the designer and contractor that it is normal to expect some amount of cracking and curling on every project, and that such occurrences do not necessarily reflect adversely on either the adequacy of the floor’s design or the quality of its construction”
Some reasons as to why concrete cracks can be due to:

• Plastic shrinkage cracks
• Cracks due to improper jointing
• Cracks due to continuous external restraint
• Cracks due to lack of isolation joint
• Cracks due to freezing and thawing
• Craze cracks or crazing
• Settlement cracks

The three most common types of concrete cracks are: 
Shrinkage Cracking

• Plastic shrinkage concrete cracks when that water eventually leaves the slab, it leaves behind large voids between the solid particles. These empty spaces make the concrete weaker and more prone to cracking. This type of cracking happens frequently and is referred to as “plastic shrinkage cracking

Settlement Cracking

• Settlement cracks happen when the ground beneath the slab wasn’t compacted properly and part of the concrete sinks. Settlement cracks wider than a credit card, or that run through the entire slab require repair or replacement of the concrete.

Craze Cracking

• Craze cracks on concrete is when the surface of concrete develops a lot of fine cracks. Sometimes called map-cracking or alligator cracking, crazing of concrete is a result of conditions and curing methods at the point the concrete is laid or even the way it is finished.

Unfortunately some concrete cracks cannot be avoided and do not always attest to the workmanship of the project. If you have a crack in your concrete and are wanting to know if it is worth it to replace and pour new concrete, give A-Concrete a call and we would be happy to talk more with you about your options. We service the entire Northern Colorado area and do a range of both commercial and residential concrete projects.