What Are Concrete Shrinkage Cracks?

Are you noticing small hairline cracks in your sidewalks, driveways, or poured concrete foundation walls? If so, these are likely the result of concrete shrinkage. Cracks caused by shrinking are common in new construction and renovations. In this blog post, we’ll explain why hairline cracks are normal in newly poured or repaired concrete surfaces and how to evaluate when a crack needs professional attention.

What Are Concrete Shrinkage Cracks?

Concrete shrinkage cracks are a common issue that occurs when concrete experiences a volume reduction due to water loss during the curing process. This can cause the concrete to shrink and crack. Most shrinkage cracks are hairline and not structurally significant.

The Most Common Cause of Concrete Shrinkage Cracks

The leading cause of concrete shrinkage cracks is the rapid loss of water content in freshly poured concrete. As the water rapidly evaporates from the concrete surface, the surface dries faster than the rest of the slab. This can cause concrete to crack. Pouring concrete during hot, dry weather exacerbates this. Concrete with a high water-cement ratio is more prone to shrinkage cracking, as the excess water evaporates quickly and causes the concrete to shrink and crack. However, even properly mixed and poured concrete can experience shrinkage cracking if the curing process isn’t managed correctly or if environmental factors beyond the contractor’s control impact the curing process.

While concrete shrinkage cracks in a poured concrete foundation wall aren’t structurally significant, they can allow water to seep into a crawl space. Therefore, they should be sealed.

Concrete Shrinkage Cracks Are More Likely to Happen If…

Various factors can contribute to concrete shrinkage cracks, but hot weather, windy conditions, and excessive water in the concrete mix are the most common culprits.

Hot Weather

Concrete shrinks faster than usual during hot weather as it dries out more quickly.

Windy Conditions

High winds can also accelerate drying, leading to more significant shrinkage and cracking.

Too Much Water in the Concrete Mix

A mix with too much water increases the likelihood of shrinkage cracking and may also affect the durability and strength of the concrete.

It’s essential to take steps to minimize concrete shrinkage cracking. This includes avoiding pouring concrete in hot or windy conditions and using appropriate mix designs, such as those that contain shrinkage-reducing additives. Proper curing is also essential to help prevent shrinkage cracks.

Do Shrinkage Cracks Look Different From Other Foundation Cracks?

Cracks caused by shrinkage during the concrete curing process are usually very thin hairline cracks.

When it comes to poured concrete foundation walls, it’s essential to identify the difference between shrinkage cracks and other types of cracks that are much more serious. Signs a crack in a poured concrete foundation wall is not caused by shrinkage, include the following:

• One side of the crack is higher than the other, This type of crack usually indicates structural damage caused by foundation movement.
• A crack accompanied by corrosion, Corrosion indicates the reinforcement steel is damaged, which may cause a significant structural issue if it isn’t promptly addressed.
• Any crack wider than 1/16 inch, Cracks wider than hairline are not shrinkage cracks. Typically, shrinkage cracks are less than 1/16 inch in width. Cracks wider than that are usually an indication of structural damage.
• A crack that follows a single line, These cracks are usually structural. Shrinkage cracks tend to be discontinuous.

Concrete Slabs Can Crack for Reasons Other Than Shrinkage

Not all cracks in a concrete slab (sidewalks, driveways, patios etc.) are caused by shrinkage. Other common causes of cracks in concrete slabs include the following:

• Not enough control joints, Control joints are designed to help regulate the natural movement of the concrete as it expands and contracts due to changes in temperature and moisture. Without enough control joints, the pressure generated by this movement can cause cracks to form.
• A weak concrete mix, If the concrete isn’t mixed correctly, or the aggregate used is of poor quality, the resulting material may be more prone to cracking and deterioration over time.
• Hot weather, Hot weather can cause the concrete to expand and push against anything in its way. This can cause cracks to form.
• Freeze-thaw cycle, This process occurs when water enters the concrete and then freezes, causing it to expand and push against the concrete. The freeze-thaw cycle is most common in regions with extreme temperature swings.
• Invasive tree roots, We’ve all seen examples of tree roots pushing up on a concrete slab and causing it to crack.
• Expansive soil, Expansive soil contains a lot of clay, and because of this, it swells as it soaks up moisture and then shrinks as it releases moisture and dries out. This creates movement under the slab and can eventually lead to cracking.
• Erosion-prone soil, If the soil under the concrete is prone to erosion, voids can form. If the slab sinks into the voids, it can crack.

For more information, see signs of uneven concrete slabs.

If you’re concerned about cracks in a concrete slab or a poured foundation wall, contact us today to schedule an evaluation and receive a repair estimate. We serve Southern California, Arizona, and Nevada.

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Foundation movement is easier to judge in person than from a photo. Schedule a free evaluation and a Dalinghaus specialist will walk the property with you and explain what the evidence shows.