Why Does Concrete Crack?
Tuesday, November 15th, 2022 by Kelly Neuhaus
Whether it is new or old, it's inevitable - Concrete always cracks.
Concrete is the most common material used for driveways and sidewalks around the world. It is known for its durability and longevity. So, this begs the question - If concrete is so strong and long-lasting, why does it crack?
How is concrete made?
Before we get into the why, it is important to know what concrete is made of. There are different types of concrete, but they are all made up of three basic components: water, aggregate (rock, sand, or gravel), and Portland cement.
Now you may be thinking, water? Why is water in my concrete?
While we could write a whole blog on the science behind why this is not chemistry class, so we will spare you scientific details and get to the point. Water is the key ingredient in binding the aggregate and cement into a paste to make it workable.
If there is too much water, it can reduce the strength of the concrete. The concrete can become stiff and hard to use if there is too little water.
Just like baking, you need to have the correct measurements of liquid and dry ingredients to make your perfect batter.
But why does concrete crack and can I prevent it?
Weather, water, and earth. These natural elements have a big say in if your concrete will crack. Hot and cold weather can be harsh on your concrete, creating pressure and cracks. Water can be pesky, going where it shouldn’t. And the soil it is sitting on can be damaging from the start. Below are the top 5 reasons concrete can crack and steps you can take to help prevent it.
Shrinkage: Imagine a sponge. When it is filled with water, it gets larger, and over time the water evaporates, dries the sponge out, and shrinks. This is very similar to what happens to concrete. As the concrete dries and hardens, some water within the concrete will start to evaporate, just like your sponge. When the concrete starts to shrink, the pressure can cause cracking. One of the best ways to prevent this is to find a contractor you trust to mix the concrete correctly. Over the first few days after the pour, you can spray the concrete with water to prevent the water from evaporating too quickly.
Expansion Cracks: During hot weather, concrete heats up and expands. This is like running a tight metal lid under hot water to expand the lid and help you open the jar. The metal lid has all the room it needs to expand, but when concrete expands, it usually does not have much room to budge. This will cause pressure throughout the concrete slab, and cracks can appear. Two things to help this issue are cutting control joints and installing an expansion joint. Control joints help predict where the concrete will crack and help keep the integrity of the slab. Expansion joints will help relieve pressure when the concrete starts to expand, not allowing too much pressure throughout the slab.
Heaving Cracks: During cold weather months, the moisture in the ground under the slab will freeze, and the slab itself can shrink, causing the concrete to lift and heave. This puts pressure on the concrete and causes it to crack. To help prevent more moisture from getting below the slabs and freezing, it is best practice to caulk the control joints and seal the top. This will help prevent moisture from seeping into the concrete and freezing during the winter.
Settlement Cracks: Settlement cracks typically occur when voids are created under a concrete slab. This can happen if the soil is not compact under the poured slab or when water from downspouts or rain seeps through the control joints and washes away the soil underneath the slab. This then causes the heavy concrete to start to sink, and the pressure causes cracking. Very similar to preventing heaving cracks, those preventative measures can also help settlement cracks. When water and moisture are not allowed to get under the slabs, there is a better chance the soil will not wash away.
Excessive Weight: Concrete is a very strong material, but it is not indestructible. Anything excessively heavy on top of the concrete can cause cracking. In residential areas, this usually is not a problem. Heavy snow can be a problem, the ground is soft, and the extra weight on the concrete slab can press it down and start to crack. Do your research! There are different strengths of concrete depending on where it is poured. Check with your contractor to see your slabs' weight limits.
What if my concrete is already cracked?
If you are already seeing signs of cracking or cracks, getting a professional involved is best. Concrete problems only get worse and will not fix themselves. Here at Thrasher Foundation Repair, we offer multiple preventative measures that can help the issues you are already seeing. The products that are included in our Concrete Protection Systems; PolyLevel(R), NexusPro(TM), and SealantPro(TM).
PolyLevel(R) is a high-density polyurethane foam that is waterproof, environmentally friendly, and long-lasting. This helps to lift and level concrete by injecting the foam beneath the slab through penny-sized holes. The foam will start to expand and harden, lifting the slab into place while also compressing the surrounding soil. Compared to traditional mudjacking, PolyLevel addresses the stability of the slab, allowing a more permanent solution. After PolyLevel(R) is installed, we use NexusPro(TM).
NexusPro(TM) is our UV-resistant silicone-based crack and joint sealer. This is applied like caulk, but it works better than the traditional big-box brands, as NexusPro(TM) won't crack, bubble, or dry out. NexusPro(TM) can also prevent water from flowing under the slab, creating weaker soil and washout. The best thing about these two products is they both have a very quick curing process. Within a matter of hours, you can use your concrete as normal.
The last product of our Concrete Protection System is SealantPro(TM). This is applied as a top coat to protect your concrete against the elements and permanently bonds to your concrete. These big 3 also come with a big warranty of 5 years!