What Causes Cement Concrete to Crack? Here’s the Scoop: A blog about how to keep cement concrete from cracking.
Do you know why most cement concrete starts to crack shortly after it’s been poured? And what you can do to prevent it from cracking? Most people don’t know. Here’s the scoop.
There are three major reasons your cement concrete is cracking:
1. The soil under your concrete slab shrinks, swells and shifts over time, due to changes in moisture content and temperature;
2. The steel reinforcement bars (rebar) inside your cement slab shrink and expand when temperatures change;
3. Your cement slab dries out as it cures; this causes it to shrink slightly as well.
These factors cause slight movement as the cement contracts and expands with temperature changes, which causes hairline cracks throughout the surface of your slab. These cracks allow water to seep into the soil underneath your slab and cause further settlement, heaving, and eventually more cracking.
When it comes to concrete, you don’t want any cracks. What causes cement concrete to crack? In this blog, we’ll tell you the scoop on how to keep cement concrete from cracking and why cement concrete cracks.
We’ll start by explaining what happens when concrete is mixed and cured. The water in the mix activates the hydration process, which starts when the water mixes with cement powder. The water stimulates a chemical reaction that produces calcium silicate hydrate gel and heat. The gel is formed by combining calcium, silicon, oxygen, and hydrogen. This gel attaches to sand particles and forms a paste that binds them together. When all of the water in the mix has evaporated, the hardened concrete is left over.
Concrete is made up of cement and aggregate. Aggregate refers to gravel or crushed stone that makes up between 60% and 70% of ready-mix concrete. Typically made from limestone, granite, gravel or a combination of these materials, aggregates are chosen for their hardiness and durability, as well as their porosity (the ability of water to pass through).
When a slab of cement concrete is poured improperly or exposed to extreme weather conditions before it is fully cured (dried), it can develop unsightly cracks or worsen existing
What Causes Cement Concrete to Crack?
Cement concrete, like any other material, will crack. The most common reason for a material to crack is stress. Stress is caused by the expansion and contraction of the material due to changes in temperature and moisture conditions. This article discusses the reasons why cement concrete cracks and what can be done to minimize cracking.
What are the Reasons for Cement Concrete Cracking?
The primary cause of cracking in cement concrete is drying shrinkage. This occurs when water evaporates from the surface of the concrete resulting in volume loss and corresponding shrinkage of the concrete. For this reason, it is important to keep newly placed concrete wet with a spray of water or fog mist during curing.
Often, there are too many reasons to blame one single culprit. Here are some of the reasons why concrete may crack:
Formwork that is not rigid enough or strong enough to resist the forces exerted by plastic concrete, placing methods that cause segregation or honeycombing, a subbase that does not provide adequate support (e.g., soft, unstable subgrade), reinforcing steel placed too close to the top surface, excessive loads on the slab from heavy equipment or vehicles when the slab was still too young and weak, improper joint spacing at
As we discussed in the last post, concrete is a versatile and durable building material that is ideal for many commercial and industrial applications. It can be used to create a floor, foundation or wall; it can be poured or sprayed; it can be smooth or textured; and it comes in a wide range of colors.
So what causes cement concrete to crack? The truth is: there are a lot of reasons why concrete cracks, and some are easier to address than others. Let’s take a look at some of the most common ones.
Drying Shrinkage. Drying shrinkage happens when water evaporates from the surface of cement paste, leaving the paste with less volume than before. This contraction causes the surrounding concrete to crack, creating hairline fractures along the surface.
Thermal Contraction. As we mentioned above, water expands when it freezes (this is why pipes burst in cold weather). When this happens inside your cement slab or foundation, it can cause the concrete to crack.
Plastic Shrinkage Cracking. Like drying shrinkage, plastic shrinkage happens when water evaporates from the surface of wet cement paste before it has hardened completely. Unlike drying shrinkage though, this type of cracking occurs before the
Whether you’re a homeowner or a home builder, you don’t want to see concrete crack. But it’s inevitable. The thing is, how you handle the problem will determine whether your concrete cracks or not.
If you’re a homeowner, there are two things you should do when repairing concrete:
1) Find out why the concrete cracked in the first place, and 2) Take steps to keep it from happening again.
If you build homes, knowing why concrete cracks will help you avoid future problems.
Let me explain what causes concrete cracks and how to prevent them. If you’re planning a home improvement project, especially one involving concrete (like building a patio), be sure that you know what to look for when buying the right concrete product for your job.
Cracks are the most common problem in concrete. It’s a complex material that is a result of a complicated chemical reaction and as such, cracks can occur due to many different reasons. We will cover 10 of the most common causes.
1. Shrinkage Cracking.
2. Settlement Cracking.
3. Plastic Shrinkage Cracking.
4. Restraint Cracking.
5. Reinforcement Cracking
6. Thermal Cracking
7. Corrosion Cracking: steel corrosion is an electrochemical process and as such, it requires water and oxygen to occur, which means that corroded rebar within concrete may have initiated due to moisture penetration through cracks and other defects (micro cracks). This type of crack is often associated with the corrosion of steel reinforcement in concrete structures where moist air flows into the structure along or across the surface or through cracks and penetrates into the concrete matrix to reach the embedded steel rebar, which becomes corroded over time and increases in size by up to eight times its original size causing cracking of surrounding concrete and spalling (delamination) of concrete from around the rebar and possible failure of the structure under load conditions if not treated or repaired quickly enough (Figure 3).
Concrete cracks. It’s a simple fact of life. The question is: are those cracks indicative of a serious problem or just normal shrinkage? In this article by ACI 302, “Guide to Concrete Floor and Slab Construction”, the authors state that “Shrinkage cracking cannot be eliminated.” The key is to understand the causes and control them as much as possible.
ACI Committee 302 defines curling as a distortion of the flatness of a floor. Curling is often confused with warping, which refers to twisting or distortion in plane. However, if both curling and warping are present, it is usually referred to as warping. It is important that construction joints in slabs-on-ground should be located where they will not affect the appearance of the floor. For example, if the flooring material has an organic surface such as vinyl composition tile (VCT), laminates, rubber sheet goods, linoleum or wood, then the construction joints should be located so that they will not interfere with the pattern on the finished flooring. If there are no special requirements for joint location, then it is best to locate them in areas where they will be easy for maintenance personnel to keep clean because there will always be an
panyam is a contributor at PanyamCements. We are committed to providing well-researched, accurate, and valuable content to our readers.
