Concrete is strong but can crack due to temperature changes, weak structures, or tree roots. Identifying the type of crack helps in proper repair.
Fresh concrete is easily shaped but is weak and can crack. It expands and shrinks with temperature changes. Without proper design, cracks will appear. A well-planned design is the only way to prevent them. In this Brick & Bolt article, we will explain the causes and types of cracks formed in concrete slabs to help you resolve the issue quickly.
Severity of Cracks
Roads, bridges, and many other structures are built using concrete. Concrete cracks just like any other thing in this world. Concrete cracks frequently and are caused by many reasons with varying intensities.
Non-Structural Cracks
Usually, non-structural cracks don’t cause any damage to the structure as they are tiny, hairline fissures. These cracks occur due to dryness, temperature fluctuations, or mild stress. Even though they don’t harm anything, they should nevertheless be fixed for longevity.
Structural Cracks
Structural cracks are severe and cause structural damage. They should be fixed immediately when you find them. Ignoring them could cause the structure to deteriorate and possibly collapse.
Types of Cracks in Concrete Slabs
Here we will discuss the different types of cracks that can be found in concrete slabs as follows:
Plastic Shrinkage Cracks
These cracks happen when the top layer of concrete dries too fast before it fully sets. This usually occurs in hot, dry weather or if there isn’t enough moisture in the mix. As a result, the surface shrinks too quickly, creating a network of small, random cracks. While they don’t go deep, they can make the concrete look uneven and weaken its durability over time.
Crazing and Crusting of Concrete
- Crazing Cracks
Crazing cracks resemble fine webbing over the concrete surface. This occurs when water may evaporate too fast, or there could be a short setting time because of hot weather, low humidity, wind, and direct sun. Such cracks are primarily small, without affecting the structure.
- Crusting Cracks
Crusting cracks are deeper and wider. They form when the surface dries too fast, creating a hard layer while moisture remains trapped inside. The surface cracks as moisture escapes, often caused by overworking, poor curing, or excess water.
Settling Cracks
Settling cracks are usually caused by ground movement or settling of the soil under the concrete. They are normally caused by bad soil preparation and erosion. Such cracks will result in uneven surfaces and a tripping hazard that increases the damage over time. It can be prevented if the soil is well prepared, with proper drainage, and correct installation.
Expansion Cracks
These cracks happen when concrete stretches and shrinks because of changes in temperature and moisture. They usually appear as straight lines across the surface. Extreme weather or missing expansion joints can cause them. While they don’t usually weaken the structure, they can let water in, leading to more damage over time. Using proper installation techniques and expansion joints helps prevent these cracks.
Heaving Cracks
These cracks happen when the ground beneath the concrete moves or swells, pushing it up, often due to weather changes or freezing and thawing. Heaving cracks can damage concrete and nearby structures like walls and foundations.
To prevent them, proper drainage, soil preparation, and good installation methods are needed. If these cracks appear, fixing the root cause is important to stop further damage.
Overloading Cracks
These cracks happen when concrete carries more weight than it can handle, like heavy machines, vehicles, or too much foot traffic. They can be dangerous because they weaken the concrete and nearby structures. To prevent them, proper weight distribution, reinforcement, and regular maintenance are important.
If these cracks appear, fixing them quickly and using stronger concrete can help keep the structure safe.
Corrosion of Reinforcement
These cracks happen when the steel inside the concrete rusts, expands and causes the concrete to crack. Moisture, salt, or other harsh materials can cause this. If not fixed, it can weaken the structure. Using the right concrete mix, proper placement, and regular maintenance can help prevent this. If corrosion starts, fixing it quickly is important to avoid further damage and ensure safety.
Causes of Cracks
Concrete cracks occur due to plastic shrinkage from rapid moisture loss, improper curing, and rapid drying in hot or windy conditions. Soil movement, poor compaction, and erosion cause settling cracks. Expansion and contraction from temperature changes lead to cracks without proper joints.
Freeze-thaw cycles create internal pressure, weakening the concrete. Overloading from heavy vehicles or machinery exceeds concrete strength, causing fractures. Corrosion of reinforcement due to moisture and chemicals results in cracking.
Poor construction practices, excess water in the mix, and weak reinforcement reduce durability. Chemical reactions and structural design errors further contribute to crack formation over time.
How to Fix Cracks in Concrete Slabs
Polyurethane foam is applied to fill the cracks in the concrete foundation slabs. Mostly cracks and uneven surfaces happen because of excessive or insufficient water in the soil. Poor drainage makes the soil too wet, while drought dries it out completely, making the foundation shift and crack. This is known as “differential settlement.” Slab piers are installed under the foundation to reach strong, stable soil. These piers help lift and support walls that have started to sink, preventing further damage and keeping the foundation strong.
Conclusion
In conclusion, concrete can crack for many reasons, both structural and non-structural. Some cracks are harmless, while others can be serious and weaken both the concrete and nearby structures. Prevention and prompt repair are crucial to managing concrete cracks effectively.
It’s important to identify potential issues early and find the right solutions before the cracks worsen. Small cracks may be of little concern, but larger ones could indicate underlying structural issues.
Check your interior concrete (floors, garage, foundation walls) and exterior concrete (driveways, pool decks, exterior foundation walls) regularly for new cracks. Get those small cracks repaired as quickly as possible.
FAQ’s
The two most frequent reasons for cracks in concrete slabs are settlement and early drying. When concrete loses moisture too quickly, shrinkage happens. Settlement occurs when the slab experiences unequal pressure due to shifting or sinking earth beneath it.
Use concrete patching material after cleaning small fractures. Installing slab piers or using slab lifting methods like polyurethane foam to raise the foundation may be necessary for larger fissures.
Usually, serious fissures are large (more than 1/4 inch) or exhibit evidence of water seeping in. These might be signs of instability, foundation movement, or structural problems.