With its unique combination of strength and malleability, concrete has become a popular material for projects ranging from elaborate sculptures to the sturdy foundation of a house. However, like many other materials, concrete can be subject to the effects of expansion and contraction due to temperature fluctuations.
This article will discuss the causes and effects of these changes in further detail.
When exposed to extreme temperatures, concrete undergoes an expansion or contraction process that affects its stability. In cold temperatures, water molecules in the concrete move closer together, causing it to shrink and become more brittle.
In hot temperatures, the opposite occurs – the water molecules move further apart, leading to an expansion of the material as well as a decrease in strength. This change is known as thermal expansion or contraction.
Why Does Concrete Expand or Contract?
Understanding the cause of thermal expansion or contraction in concrete is essential for predicting and controlling the effects of temperature changes on a structure.
The most common explanation for this phenomenon lies in the difference between the thermal coefficient of expansion (TCE) of water and cement. Cement has a higher TCE than water, meaning that it expands more when exposed to heat than water does.
This causes the cement to push out against the water, resulting in an expansion of concrete.
The effects of thermal expansion or contraction can be minimized by controlling the temperature at which the concrete is poured, cured, and stored.
In addition, additives such as shrinkage-reducing admixtures (SRA) can be used to reduce the amount of thermal expansion or contraction experienced in concrete.
With that being said, there are two types of concrete: reinforced and non-reinforced concrete. In terms of expansion and contraction, reinforced concrete is generally more stable than non-reinforced concrete.
This is due to the fact that reinforced concrete has steel bars or wires embedded within it, creating an additional layer of stability and protection against temperature fluctuations.
What Are the Effects of Thermal Expansion or Contraction?
The effects of thermal expansion or contraction can have a significant impact on the integrity of a structure if not taken into account when constructing a structure. The most common effects of thermal expansion or contraction are:
Cracking or Spalling
When the concrete expands or contracts, it can cause the material to crack and spall (or chip away).
This can lead to structural instability and require expensive repairs down the line. During the curing process, the concrete can be subject to increased cracking or spalling if not given enough time to settle.
Uneven Settling
Due to the varying rates of expansion and contraction in different parts of a structure, it is possible for sections of the concrete to settle at different levels. This can cause an uneven surface that will need to be leveled during the finishing process.
Displacement of Joints
If the concrete is not properly reinforced, the thermal expansion or contraction can cause displacement of joints, leading to water leakage, mold growth, and other structural problems.
How Much Does Concrete Expand or Contract?
Minimal thermal expansion or contraction in concrete is expected and generally considered within the allowable limits for most projects.
The amount of expansion or contraction experienced by a structure will depend on the type of concrete used, the temperature it is exposed to, and the length of time it is exposed to these temperatures.
Generally speaking, non-reinforced concrete can be expected to expand or contract by up to 0.2% for each 10°F change in temperature. Reinforced concrete can experience slightly less expansion or contraction, with an expected range of 0.04 – 0.1%.
The best way to avoid this problem is by making sure that you have a thorough understanding of how much concrete will expand or contract when exposed to different types of weather conditions.
It doesn’t matter what type of project you’re working on–you’ll always want to make sure there is plenty of room for any changes that could happen with concrete. It’s important to know how much it will change to plan accordingly.
For example, if your slab is going over a crawl space, you should leave room for expansion. If you don’t, then the chances are that your floors won’t fit in the house when it’s time to be installed.
There are many other examples of how different material thicknesses can cause problems with concrete expansion and contraction.
Different Types of Concrete Materials Used in Construction
First, you need to know what types of materials your concrete is made from. There are three main types:
- Portland cement-based cement.
- Fly ash-based cement.
- Slag and ash-based cement.
The material you use will play a major role in the expansion and contraction of your concrete. The Portland cement-based cement will expand and contract more than fly ash or slag and Ash-based cement due to the material’s chemical makeup.
If you don’t know what type of cement was used, contact your local building supply store or construction company for more information.
Does Concrete Expand When It Dries?
Concrete expansion and contraction are often caused by temperature changes, but they can also be caused by drying. So yes – concrete will expand when it dries.
The amount of expansion or contraction can depend on temperature, humidity, and other environmental factors. Although these changes are usually minimal, it’s important to factor them in when designing and building a structure.
In a nutshell, while the concrete is wet, it’s still reacting to the environment. As time progresses, the concrete will react less and less to the environment and start to settle into its desired shape. This means that there is still a chance of some slight expansion as it dries, and you should always factor this into your plans. However, it is usually minor and shouldn’t cause any major issues.
When you’re pouring concrete under certain weather conditions, you need to allow additional time for it to completely dry if you want it to be stable.
For instance, when temperatures are above 75 degrees Fahrenheit at night or higher than 115 degrees during the day, your freshly poured concrete needs more time to dry.
If there is ample time for drying (at least 12 hours), then these warmer temperatures won’t affect its stability too much; however, if you’re using older methods that don’t provide adequate drying time (less than 3 hours), then your new deck could be unusable due to expansion in hot weather.
You’ll also need more time for drying in humid environments like Florida, where they experience high dew points year-round (85% humidity level).
In low-humidity climates like Nevada, with a 30% humidity level at night and 40% during the day, your new deck should last just fine without profound changes or cracks from
Does Concrete Expand When It Gets Wet?
Concrete can also expand when it gets wet. When the concrete is exposed to rain or high humidity, it will absorb water, causing it to swell and expand.
As a result of this process, the concrete can crack, become brittle, and ultimately fail if the proper precautions aren’t taken. The amount of expansion caused by moisture absorption depends on the type of concrete and the environment it’s exposed to.
To prevent cracking and other issues due to moisture absorption, make sure that you seal your concrete properly after installation; this will help keep water from seeping in and causing damage.
Additionally, make sure that any drainage systems around the area are working properly so that excess water isn’t pooling around the concrete.
Here are some additional factors that can affect the expansion and contraction of concrete:
- Climate: More humid climates will cause more expansion than drier climates.
- Type of Concrete: Higher-quality concrete will tend to expand less than lower-quality concrete.
- Construction Sequence: Construction sequence can have an impact on how much the concrete expands when it dries. This is mainly because of the way the concrete is layered and its position relative to other materials.
- Joints: The joints in the bottom of a slab can affect how much water is able to escape when the concrete dries, which affects how much it will expand.
- Slump/Thickness: The slump or thickness of the slab can also have an effect on how much it expands.
Does Concrete Expand or Shrink During Summer
The short answer is yes; concrete will expand or shrink depending on the season. Since we’ve already established that concrete expands when wet, it stands to reason that it will expand in summer when temperatures rise and humidity increases.
If the temperature is hot enough and the humidity is high enough, then it can cause the concrete to swell significantly, which could lead to cracking or other structural issues.
On the other hand, cooler temperatures can cause concrete to shrink. When the temperature drops and humidity decreases, the moisture in the concrete will evaporate, causing it to shrink.
Conversely, when exposed to dry air in the winter, the pores lose moisture and shrink. If you’re working with concrete on your home project, use these points to help you determine how much of an expansion/contraction you should expect for your project
Does Concrete Expand or Shrink During Winter
The amount of concrete that will expand or shrink in different seasons is dependent on the type of material it’s made up for. However, there are thresholds where concrete will expand or shrink by more than 1/2 inch in one day. Here are some examples:
- Concrete will not contract in the winter because the temperature is too cold to cause it to shrink. While temperature and cold weather can cause concrete to become brittle, it won’t actually shrink. However, the cold winter temperatures can cause the ground beneath your concrete to heave and contract. This will cause the concrete slab above it to rise or fall, leading to cracking and other structural issues.
- Concrete can contract up to 1/2-inch in a day when exposed to high heat in the summer. This is because the temperature change causes water to evaporate out of the pores of the concrete and make it shrink.
Concrete will never expand in the winter, but it can expand up to an inch in a day when exposed to high heat in summer. This expansion occurs due to water evaporating out of the pores and causing bubbles on its surface, which makes it swell.
How Can You Keep Your Structure Safe From Expansion and Contraction?
To prevent your concrete structure from expanding or contracting too much, there are a few steps you can take.
- Make sure the surface of your concrete is sealed properly to keep moisture out and prevent it from absorbing more water than it needs.
- Install drainage systems around your concrete slab so that excess water doesn’t pool around.
- Add expansion joints in your concrete that allow it to move without cracking.
- Use high-quality concrete when pouring the slab, which will be more resistant to changes in temperature and humidity.
- Make sure the construction sequence is correct, as this can affect how much your concrete expands or contracts.
- Finally, check for any signs of cracks or damage to your concrete and fix them before they become bigger problems.
- It might be helpful to install metal straps on any rebar used in the construction process. These straps will prevent the reinforcement bars from bending out of shape if they’re exposed to extreme temperatures or moisture levels for an extended period of time.
Concrete Expansion and Contraction: Final Thoughts
While it may seem like more work up front, following these steps will go a long way in protecting your concrete structure from expanding or shrinking too much due to seasonal fluctuations.
By taking the necessary precautions and understanding how temperature, moisture levels, and construction sequence affect your concrete’s expansion and contraction, you can ensure that your structure is safe from any structural damage caused by weather-related issues
