What Causes Concrete to Crack?

There are many factors that cause concrete to crack. Some of the factors that can cause concrete cracks are:

• Drying Shrinkage – as concrete cures and goes through it’s chemical reaction between the water and cement particles it begins to “dry” out. As with most materials that dry out they begin to shrink causing hairline cracks to appear.
• Thermal Shrinkage – all materials shrink and expand with changes in temperature. As concrete cools down (the chemical reaction that’s created when water and cement is mixed creates heat) it shrinks. The shrinking from cooling down can also cause hairline cracks to appear.
• Restraint – This topic is a bit harder to explain but it’s caused when concrete is confined and prevented from moving due to the structure. If the concrete wants to move due to loading, thermal or other effects and it’s restrained from doing so it will crack.
• Settlement – If the ground around a foundation settles it can cause the concrete to crack. Settlement can cause significant damage under certain circumstances.
• Loads – As I mentioned when concrete is subjected to loads that cause tension it will crack the concrete. Tension can be caused by many different loading conditions and it’s best dealt with by designing reinforced concrete that uses rebar.
• Corrosion – When steel rebar corrodes inside of concrete it expands and causing the concrete around it to crack.

When is a Concrete Crack a Potential Problem?

Obviously this is a topic that has many answers and not easily answered in a simple way. However, what you need to know is that ALL concrete cracks. In fact, reinforced concrete must crack before the rebar can take hold and do it’s job. Most cracks are so narrow that you can’t see them unless you look very closely with good light.

So which cracks are bad? Typically if you see a concrete crack that’s less than 1/8 inch wide then I’d say you can totally ignore it. If you find a crack that’s between 1/8 inch and 1/4 inch wide it is most likely nothing to worry about. The width at which they became a problem requiring repair often depends on the following factors:

• Is the crack static or is it gradually becoming wider? If you notice movement of the crack, it may continue to widen if the crack isn’t repaired and could indicate a structural problem.
• If the crack is in a horizontal surface, such as a floor or slab, is it wide enough to present a tripping hazard?
• In foundation walls or slabs, is the crack wide enough to allow moisture seepage? 
• Does the crack trap dirt and present a maintenance or sanitation issue?
• Is the crack an eye sore and located in a high-visibility area?

 Consult an engineer or concrete repair professional to determine the cause of the crack and to recommend the best repair solution.

Easy DIY Repairs

Minor cracks in concrete can be repaired easily by DIY home owners. Concrete cracks can be filled / sealed using a number of products. I happen to like concrete crack fillers. You can also use hydraulic cement (it expands slightly as it cures) to fill cracks. The idea behind filling the cracks is to seal them up to prevent moisture and air from moving into the concrete.

I hope you found this information use. Please feel free to share.

Best regards,
WIlliam