What Causes Concrete to Crack, and When Should You Worry?
Cracks in Concrete Are Common. That Does Not Mean You Should Ignore Them.
Almost all concrete surfaces crack at some time. Concrete surfaces, including driveways, patios, pool decks, and building foundations: wherever there is concrete, there will be cracks. When most homeowners notice a crack, they begin to wonder if it is a major structural issue or if it is a normal movement of a material that has been exposed to the heat, cold, and every condition in between in the State of Arkansas.
The straightforward answer is it depends on the kind of crack, its place, and the reason for the crack. There are cosmetic cracks that will need only monitoring. Others are warning signs of a potential problem that may cost a lot more if not corrected. At Planit Dirt Excavation and Concrete, the team has worked with and seen all forms of concrete over the past 37 years in a 50-mile radius of Jacksonville, AR. This is what you really need to know.
Why Concrete Cracks in the First Place
Concrete is a strong material under compression but weak under tension. It cracks when it is pulled, twisted or subjected to unequal forces. Knowing the most common causes can help you determine what you are seeing when a crack appears.
Shrinkage During Curing
Water is a component of the concrete during mixing. During curing, the amount of water in the slab will shrink due to evaporation. This shrinking causes the concrete to be under internal stress that it may not be able to withstand without cracking. This is one of the most frequent reasons surface cracks develop and is unavoidable without taking steps to prevent them; experienced concrete contractors create control joints, or deliberate cracks that are cut or formed into the surface, that provide a known place for the concrete to crack instead of allowing it to do so by chance.
If cracks develop along or near control joints, this is what they are intended for. It is not a defect. It is the system working as intended.
Settlement and Ground Movement
Soil conditions differ greatly from one region to another in Arkansas. Concrete slabs placed on expansive clay soils are subjected to cyclical stresses due to expansion and contraction of the soil during wet and dry weather conditions. Another significant factor is inadequate compaction when preparing the site. If the subbase under a concrete slab is not compacted properly prior to the concrete being poured, the ground will settle unevenly afterwards and the slab will be forced to follow.
This kind of movement usually creates cracks that run diagonally, at the corners of slabs or lower a part of the slab compared to the surrounding slab. These cracks are important to address since the underlying soil problem will cause more movement unless addressed.
Freeze-Thaw Cycling
With the temperature variations that Central Arkansas experiences, freeze-thaw cycling is a true concern for exterior concrete. Concrete has minute pores in its surface through which water can seep through. When this water freezes, it expands, causing internal pressure that the concrete absorbs through cracking. Those surfaces that have not been sufficiently sealed or are made with greater water-to-cement ratios in the mixing process are more susceptible to such damage.
Overloading
Each concrete slab has a definite load rating. Residential driveways are usually built to accommodate passenger cars and not delivery trucks or heavy machinery. If the surface is subjected to loads for which it wasn’t designed, cracks will eventually appear in the concrete surface.
Improper Installation
This one is worth saying directly. The concrete will crack sooner and more widely if mixed incorrectly, poured at the wrong thickness, cured too quickly due to insufficient protection from direct sun or wind, or finished prior to adequate bleed water evaporation. Hence, the experience and technique of the crew is as important as the material itself.
When a Crack Is Not a Problem
Not all cracks need to be treated. Hairline cracks that are no more than approximately one-eighth of an inch wide and appear in a relatively straight line with no vertical movement from one side to the other typically are shrinkage cracks. They are not travelling, they do not pose a structural problem and the concrete on either side of the crack continues to function as intended.
Sealing these cracks may prevent water from penetrating, and is recommended on driveways and exterior areas where freeze-thaw damage is a concern. But they do not require emergency attention.
When You Should Call Someone
The following situations call for proper professional evaluation of the crack instead of the watch-and-wait method.
Vertical Displacement
If you walk across a crack and sense a step, or one side is raised up compared to the other, then the slab has moved. This is nearly always associated with the movement or settlement of soil below the surface. It will not self-correct and will worsen over time.
Wide or Growing Cracks
If the crack is greater than about a quarter of an inch, or if you can see that it has grown since you first noticed it, it is an indication that the forces that created it are still active. It is helpful to have a photo of the crack taken every few months to see if the crack is stable or getting worse.
Cracks in Foundations
Cracks in the foundation of a building should be given more attention than cracks in a driveway. Horizontal cracks in walls of the basement are of special concern; they may be caused by lateral soil pressure against the wall. Differential settlement may be indicated by diagonal cracks radiating from corners of windows and door openings. If the crack is wider than a hairline, growing or water is flowing through it, it should be investigated by a qualified professional immediately.
Multiple Cracks Forming in a Pattern
A single crack in a patio slab is typically not a cause for concern. Map cracking or crazing is a network of cracks that spreads across the surface like a spider web and indicates an improperly finished surface or freeze-thaw damage. Although sometimes cosmetic, a large amount of crazing may cause water to penetrate, which increases the rate of deterioration.
Cracks in Pool Decking
Pool deck cracks that allow water to penetrate beneath the surface can cause erosion of the base material and progressive settlement. Given the wet environment pool decks operate in year-round, cracks here deserve prompt attention.
What the Right Repair Actually Looks Like
Crack repair isn’t a one size fits all option. Routing and sealing works best for stable cracks, where stopping water from entering the crack is the objective. Partial-depth repairs are used for surface damage which does not extend through the entire slab. Full depth repairs, also known as slab replacement, are suitable for concrete which has settled, heaved or degraded to the extent that a surface repair cannot resolve the issue.
In every instance at Planit Dirt Excavation and Concrete, we begin by trying to figure out why the crack has formed and then we suggest solutions. A repair that does not fix the cause is only a temporary solution, at best.
Our team of five has 37 years of concrete experience in the Jacksonville, AR region and 50+ miles surrounding the region, from restorative decorative stamped concrete repairs to building foundation installation. If you have a crack that you’re not sure about, the best first step is to get someone with expertise to take a look, rather than guessing.
Ready to Get Your Concrete Looked At?
Whether it’s a crack in a backyard patio that needs to be monitored, a driveway that has shifted and needs some repairs, or a foundation problem that requires a thorough professional analysis, the conversation begins the same way. When you reach out to us, we’ll come take a look, explain what we find, and let you the ultimate solutions.
Contact us by phone at (501) 258-5935, by email at planitdirt@yahoo.com or visit our website at www.planitdirt.com. We cover Jacksonville, AR and its surrounding area within 50 miles and free estimates are always included as part of our process.