The Benefits of Using Fly Ash in Concrete

Making the perfect concrete mix takes skill and patience, with heavy consequences that you may only realize days down the line. As a result, mastering the right ingredients and ratios to add as a concrete producer is critical to creating strong concrete bricks and staying in business. One of the most prominent ingredients of concrete is fly ash, with more than 50% of concrete laid in the US containing at least a 15% composition of fly ash.

But what does fly ash in concrete do? Our team at Lontto, a leading supplier of block and brick making machines, set out to answer just that question. We've developed this guide to help you understand what fly ash is, how fly ash is used, and its benefits.

What is Fly Ash?

Fly ash, sometimes called cement ash, is a coal byproduct usually created during the combustion of pulverized coal at power plants. It is made up of various inorganic materials, such as silica, alumina, iron, and calcium oxides. While you may think that coal ash is just a waste product, that's exactly why it's frequently used to create fly ash concrete — as a sustainable option compared to Portland cement.

Portland cement has a high environmental impact, often using tons of water, sand, and gravel to produce a relatively small amount of cement in return. Among the many beneficial uses of fly ash in concrete, it is this environmental sustainability that's becoming an increasingly popular reason to pair fly ash and concrete. Fly ash use in concrete mixture is not a new invention, either, with the Romans even leveraging volcanic ash to improve the concrete used in the Coliseum and Pantheon.

What are the Different Types of Fly Ash?

There are two main classifications of fly ash: Class F and Class C. These classes tell producers the percentage of calcium oxide (CaO), which is one of the key ingredients in forming high-strength concrete. Typically, Class F fly ash will also contain a low lime content.

• Class F Fly Ash contains less than 10% calcium oxide and is made from combusting bituminous or anthracite coal. Class F fly ash has pozzolanic properties that allow it to form cementitious properties when it reacts with calcium hydroxide while in water. Its low lime content also makes it useful for concrete that will be continually exposed to sulfates.
• Class C Fly Ash: Contains more than 20% calcium oxide and is made from combusting lignite or sub-bituminous coal. It also has pozzolanic properties but does not require calcium hydroxide to form cementitious properties in water. It's higher calcium content makes it the more popular choice for concrete construction projects.

What benefits does using Fly Ash in Concrete Offer?

Concrete mixtures that contain fly ash offer several benefits including easier workability, greater strength and durability, and a lower carbon footprint. Concrete mixers will use varying percentages of fly ash as a substitute for Portland cement, often ranging from 15 to 60% depending on the type of fly ash being used. The more fly ash added to make concrete, the more certain traits of the hardened concrete will improve.

We've outlined a few of the major benefits that mixing concrete with fly ash reaps below:

Better Workability

Fly ash is made of extremely spherical and fine particles that make fresh concrete easier to work with. This is because fine particles work to reduce the friction between the cementitious aggregates and the sand and gravel, like small ball bearings. You'll find that concrete with high percent fly ash will have a smoother finish, as well as be easier to pump from one location to another and place down.

Lower Water Demand

Water is used not only to help the reaction of fly ash and other cementitious aggregates, but also to make the mixture the right level of viscosity. Since the fly ash concrete mixes create a higher density of fine aggregates in the mixture, the water required to achieve a cohesive mix with reduced bleeding and segregating is a lot lower. By replacing your Portland cement with 20% fly ash, you'll reduce your water demand by around 10% while still creating a stronger cement concrete.

Reduced Heat of Hydration

The heat of hydration is the heat produced when a chemical reaction within your cement mixture occurs. The lower the heat, the less time it takes for your ready-mix concrete to cool. Moreover, reduced heat results in reduced thermal stresses, and a less dangerous environment for your workers. If you replace the Portland cement of your mixture, your concrete improves its heat of hydration by at least 50%.

Higher Durability

While, initially, the impact of fly ash reduces the compressive strength of your concrete, over time it will reach a higher peak of strength. For example, high-volume fly ash concrete is 80 MPa stronger than traditional cement mixtures after 56 days. The same is true for the concrete's durability and flexural strength, with fly ash concrete performing better than OPC concrete (Portland cement) in the long term.

If you want to take your fly ash cement mixture and make bricks and blocks that are highly efficient at a low price, make sure to get in touch with Lontto — your leading brick making machine supplier for over 30 years. Grab your free block machine quote now.

The Benefits of Using Fly Ash in Concrete FAQs

How is Fly Ash Made?

Fly ash is made in power plants when the pulverized coal is combusted to make electricity. The remaining fine particles are carried out using flue gasses and can eventually be used to make mass concrete.

What does too much Fly Ash Do to Concrete?

Using too much or a high percentage of fly ash in your concrete production can negatively impact certain aspects of the final product. You'll likely experience a higher setting time, more chance for poor quality control, and workability challenges from a low-viscosity mixture.

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