When installed properly, concrete is one of the most durable and long-lasting products anyone can use to build a structure. Because of its hard and durable component, it is one of the most used construction materials for both commercial and residential uses.
But not everything has to be perfect and free from flaws. Even concrete has also its flaws that can become a problem at times. The main drawback of concrete is its tendency to crack. When it gets cracked, its functionality weakens. So the question here is, why does concrete crack? What sort of phenomenon or chemical reaction causes it to happen like that? Below is an overview of why concrete cracks, and how to recognize when it needs to be fixed.
The Different Types of Concrete Cracks
So you see cracks forming on concrete, but they look different and some cracks are more concerning than others. Here’s an overview of crack types and what to do about them.
- Hairline cracks at the surface should be repaired if they are widening with time. They can be a hazard and they collect dirt. However, not all hairline cracks are signs of damage. Sometimes, they are included as part of a decorative concrete design.
- Settlement cracks happen when the ground beneath the slab wasn’t compacted properly and part of the concrete sinks.
- Structural cracks wider than a credit card, or that run through the entire slab require repair or replacement.
- Shrinkage cracks occur while the concrete is curing and can be reduced or prevented with proper joint placement.
Reasons Why Concrete Cracks
Shrinkage
After the concrete is poured, the heavier particles sink to the bottom and the lighter ones rise to the top, along with water. If the water at the top evaporates too fast, it shrinks, causing cracks in the drying concrete that weakens the overall surface.
Support Problems
This happens when rebar, welded wire mesh, tendons, and other support elements are not positioned far away enough from the surface of the newly poured concrete. If they are too close to the top, the cement pulls apart, which causes the dried concrete to crack and become less sturdy.
Ground Settlement
This usually occurs with driveways, pathways, and even cemented patios. Decomposing tree roots and other issues can create vacant spaces in the soil around your foundation, leading to settling that can crack concrete slabs. Minor settling may not be a concern, but it should be evaluated by pros to be sure your home is structurally sound.
Chemical Damage
When snow and ice cover concrete driveways and sidewalks, homeowners sometimes use salt to melt the precipitation. Unfortunately, salt is one of concrete’s weaknesses, causing pits to form on the surface. Over time, the cracks are likely to grow, making walkways unsafe to navigate.
Corrosion
Rusting steel rebar, iron rails or wire mesh can eat away at the concrete around it which causes small cracks to develop slowly and over time those small cracks turn into larger ones. When small cracks develop, it allows water to seep into the slab surface.
Overloading
Sometimes concrete cracks are not because of the concrete’s substandard quality or chemicals reacting against each other, or structural problems, sometimes concrete breaks apart because of too much weight being put on its surface that overloads the concrete underneath it. Knowing the limit of what the surface can handle is important to make sure you don’t put anything too heavy on top of it. Make sure that the concrete strength you use for whatever purpose can withstand all the heavy items you’ll put on top of it.
Expansion
Sometimes extreme weather conditions can also affect concrete’s durability. During the summer season, when the sun just burns a little bit too hot, concrete absorbs heat. When the temperature is too high, concrete expands as it gets hotter. As with all things that expand, it pushes against anything in its path. Too much expansion and the concrete may crack, leading to significant damage to both the slab and your structure.
Frost Heaving
Aside from high temperatures, temperatures below freezing can also negatively affect concrete as well. What happens is that the moisture in the ground expands causing anything above it, such as concrete, to rise several inches before the soil thaws and everything settles back down. As this freeze-thaw process repeats itself, it results in concrete cracking, which can damage the foundation slab of a home or a building.
Premature Drying
When fresh concrete doesn’t dry properly, two types of damage can occur which are crazing and crusting. Crazing cracks are thin surface fissures that look like shattered glass or spider webs. When a newly poured concrete slab loses moisture too quickly at the top, crazing can occur.
Crusting cracks normally occur while stamping and adding texture to concrete surfaces. If the stamp isn’t embedded carefully, the surface pulls apart slightly, which leaves small cracks around the outside edges. While crazing and crusting may impact the concrete’s appearance, making it either look more artful or less than perfect (depending on your preference), they don’t necessarily mean your concrete is weak and in need of repair.
