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Why Does Concrete Crack?

May 14th, 2024 | 5 min. read

By Sarah Etler

Learn about 10 of the most common causes of concrete cracking.

If your concrete is developing cracks, you’re not alone. Concrete cracking is very common, even on brand-new slabs! 

Virtually every slab will crack at some point. But why does such a strong construction material break down seemingly so easily?

This article will explain the “why” behind concrete cracking + how to prevent further damage if your concrete slabs are developing cracks.




1. Freeze-Thaw Cycles

Concrete is a porous material that easily absorbs water. When temperatures dip below freezing, it causes the water that’s been absorbed into the concrete pores to expand and pop.

As the temperature rises and the water thaws, it leaves behind surface damage and cracking where the internal expansion takes place. This creates even more surface area for the concrete to absorb water and cause damage the next time the water freezes and expands. 

Sealing Concrete To Prevent Cracks

Cracking due to freeze-thaw cycles is very common, although treating the concrete with a high-quality penetrating sealer can prevent water from being absorbed into the concrete in the first place, reducing the likelihood of cracking.

Control joints in concrete driveway

2. Not Enough Joints

In order to avoid or reduce cracking, special joints are installed in strategic locations around large areas of concrete, like patios, driveways, and walkways.

If these joints are not properly spaced or there aren’t enough of them throughout the concrete, the slabs will likely end up cracking.

Control vs. Expansion Joints

Control joints are put in place when the concrete is installed to act as a guide to control where the concrete will crack. Instead of creating a visible crack on the surface of the concrete slab, control joints help concrete crack along the straight valley of the joint.

Expansion joints are intentional spaces between two concrete slabs that allow them to move freely from one another. Without expansion joints, the constrained movement of the concrete could cause it to crack.

Related Resource: Should You Caulk Control and Expansion Joints?

Concrete patio cracking where half of the slab settled


3. Settling

Concrete can settle naturally over time due to soil compaction, water erosion, burrowing pests making a home under the slab, and more. 

All concrete settling is caused by the base of the concrete eroding away or compacting down, and as this process occurs, it can put strain or pressure on the slab, causing it to crack.

Lifting Settling Slabs To Prevent Cracking

If you notice that your concrete slabs are beginning to sink, it’s important to get them lifted up as soon as possible. As the slab settles further, there’s more pressure placed on the concrete, which can end in worse cracks.

Related Resource: All About Concrete Leveling

4. Voids

Empty spaces or voids under your concrete slabs can make them weak and prone to cracking where the slab is unsupported.

Oftentimes voids will form where erosion takes place under a concrete slab that is connected with rebar into a nearby structure, like a porch, house foundation, or adjoining slab.

Voids can also form in seemingly random places under the slab, and you may not always be able to see them.

Void-Filling To Prevent Cracks

As the base where the concrete was once supported erodes away, you can be left with an unstable slab that may crack where it’s not held up. 

Filling these voids as soon as possible after becoming aware of them can help stabilize them and reduce the chances of the concrete cracking.

Concrete slab crumbling and cracked due to heavy trauma

5. Trauma

Heavy equipment and machinery driving or parked on your concrete can cause trauma to occur, which usually involves large, intense cracks.

Residential concrete, like what’s used for driveways, is not created to withstand the weight of heavy equipment like dumpsters, large trucks, tree removal machines, etc.

Under the weight of heavy equipment, your concrete can get crushed, crack, or become weakened without any immediate visual cues.

Pro Tip: If you absolutely have to have heavy trucks, dumpsters, or other equipment on your driveway or other concrete surfaces, make sure you check the areas for voids beforehand, as these voids can potentially collapse under the weight.

6. Poor Quality Concrete

Concrete requires a delicate mix of different materials in order to create a strong, durable surface that can last for decades. A bad batch of concrete can cause concrete to crack over time. 

If some of the ingredients in the mixture are off, it can create a weaker product that doesn’t stand up to the wear and tear that concrete is put through outdoors, like freeze-thaw cycles, erosion, UV damage, and more.

Tree growing and pushing up on surrounding concrete, causing it to crack

7. Tree Roots

Trees with shallow root systems that are planted near concrete can grow underneath the slabs and cause them to lift, crack, and break apart.

These roots can continue to grow if left untreated, causing the cracking and breakage to worsen. For this reason, it’s crucial to take action against encroaching tree roots as soon as possible after noticing the problem.

Managing Tree Roots To Prevent Cracks

If you do find yourself with tree roots causing your concrete to crack, you’ll need to cut back the roots and install a root barrier system to prevent them from growing back, or remove the entire tree. 

Depending on how bad the cracking and overall damage from the tree roots is, you may also need to consider replacing the affected slabs.

Related Resource: Tree Roots Lifting Your Concrete? Here's What To Do

Pro Tip: It’s always a good idea to consult with an arborist or tree specialist to confirm how much of the tree root can be cut back without harming it.

8. Cracks in Newly Poured Concrete

When concrete is poured, it’s full of water. As the water evaporates and the concrete hardens, it causes the new concrete to shrink. Extreme weather conditions (hot and cold) in particular can worsen the effects and cause excessive shrinking. 

This shrinkage can cause small cracks in the concrete to form, which can be frustrating after having spent a lot of time and money on new concrete. However, this is a normal and very common occurrence. 

This is why it is important to select an experienced contractor whenever you are looking to have new concrete poured to ensure they have protocols in place to minimize the chance of shrinkage cracks.

9. Corrosion

When rebar or steel is placed within or through concrete, it is exposed to the elements. Most are familiar with the corrosion of steel in the form of rust. When steel rusts, it actually expands slightly. 

When water penetrates the surface of the concrete and rusts the rebar within the concrete, it puts outward pressure on the concrete, leading to cracks. 

When having new concrete installed, it’s important to be sure that the contractor is using rebar treated with a coating to protect against corrosion.

Pro Tip: Sealing the concrete can also help prevent water from penetrating the surface keeping it away from the rebar within.

Cracked and dry clay soil

10. Heaving Soils

The ground beneath your concrete can play a huge factor in the stability of your concrete. Most concrete slabs are intended to be poured on a stable bed of rock to support the heavy slab above and promote water drainage away from the concrete. 

If the concrete has been poured directly onto the soil, or the soil composition itself is high in expansive materials like clay, the slab could heave as the soil expands and contracts during wetter and dryer periods throughout the year.

As your concrete heaves up with the soil during the wetter periods, it can put stress on the concrete leading to the potential for cracks to occur. 

Help Prevent Heaving

The best way to mitigate heaving is to ensure that your new concrete has a good base that allows water drainage away from beneath the concrete. 

For existing concrete slabs, it is important to route downspouts and water flow on your property away from your concrete slabs with proper grading.

Caulking joints and cracks in the concrete slab will also allow water to run away from the area, minimizing the chances for the underlying soils to heave. 

What to Do About Concrete Cracks

If you see a crack forming in your concrete slab, there are ways to prevent it from worsening. Finding out what may be causing the cracking can help you solve the root problem.

For example, if a void under the concrete slab is what’s causing a crack, stabilizing that void with concrete leveling and then caulking the crack can help prevent the crack from getting worse or new cracks from forming.

Concrete crack repair can be done as a DIY project, but crack repair is also offered as a professional repair service.

Related Resource: How To Repair Concrete Cracks

Professional Crack Repair

If your concrete is cracked and you’re not up for attempting the DIY route, professional crack repair can help preserve your concrete. And because professionals do it day in and day out, professional concrete crack repair looks great, too.

A-1 Concrete Leveling has helped countless homeowners repair and protect their concrete from further damage. If you’d like to see what professional crack repair can do for you, find your nearest location to request a free onsite estimate!

Sarah Etler

Sarah Etler joined A-1 Concrete Leveling after receiving her Bachelor of Arts degree in English from Northern Kentucky University. As A-1's Content Marketing Manager, she works closely with industry experts to produce content that will best answer questions related to concrete repair and maintenance practices. Sarah loves living a life full of discovery and is excited every day to see what new things she can learn and share with those around her.