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A short class with Sarah and her students. The other ways are under More.
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Today, we are going to learn about fly ash, a mineral admixture. Can anyone tell me what they know about it?
Isn't fly ash a by-product from burning coal in power plants?
Exactly! Fly ash is a by-product from the combustion of pulverized coal in thermal power plants. It contains minerals like silicon dioxide, aluminum oxide, and iron oxide. Does anyone know the two types of fly ash?
Class F and Class C?
Right! Class F is pozzolanic and lower in calcium, while Class C is cementitious and higher in calcium. Remember this with the acronym 'PC' — Pozzolanic Class and Cementitious Class. Can anyone explain why these classes are important?
They affect the properties of concrete like strength and durability!
Great job! To summarize, fly ash improves the properties of concrete, which is essential for durable construction.
Now let's discuss the properties of fly ash. What do you think is important about its specific surface area?
Is it related to how reactive it is?
Yes! Fly ash has a specific surface area of around 300 to 500 m²/kg, which influences its reactivity. The finer the ash, the more reactive it can be. Who can tell me how it affects concrete?
It can improve workability and reduce water demand!
That's correct! By enhancing workability, fly ash aids in producing a smoother mix, lessening the need for water. This can reduce the overall water-to-cement ratio, crucial for strength and durability.
Let's dive into the effects of fly ash on concrete. What changes can we expect when we include fly ash?
It enhances long-term strength but might slow down early strength?
Exactly! Fly ash can reduce early strength gain, but it improves long-term strength and durability. This is particularly useful in structures where long-term performance is critical. Who can remind us of how it affects heat of hydration?
It reduces heat of hydration, right?
Exactly! This reduction is beneficial, especially in mass concrete applications, as it helps to prevent cracking. Remember, the benefits of fly ash are evident in both cost-effectiveness and sustainability in concrete production.
Fly ash helps the concrete mix, making bonds that strongly fix.
Once upon a time, in a dusty power plant, coal was burned, and from the ashes came a fine powder called fly ash, which helped concrete become strong and last long.
Remember 'FAC' for Fly Ash Characteristics: F for Fineness, A for Activity, C for Class.
PCC for Pozzolanic Class C is 'Cementitious’.
Term
What is fly ash?
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Term
Class F Fly Ash
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Term
Class C Fly Ash
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A by-product obtained from the combustion of pulverized coal in thermal power plants.
Type of fly ash low in calcium with pozzolanic properties.
Type of fly ash high in calcium with both pozzolanic and cementitious properties.
The ability of a material to react with calcium hydroxide in the presence of water to form compounds beneficial for concrete strength and durability.
The ease with which concrete can be mixed, placed, and finished.
This section discusses fly ash, its origins as a by-product of coal combustion, and its various properties and effects on concrete.
Fly ash, derived from the combustion of pulverized coal in thermal power plants, serves as an essential mineral admixture in concrete. Its two classes, Class F and Class C, possess distinct chemical compositions and impact on concrete's workability, durability, and strength.
Fly ash is a mineral admixture that is a by-product from the combustion of pulverized coal in thermal power plants. Its primary composition includes silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), and iron oxide (Fe₂O₃), which vary in proportions between two main classes:
The properties of fly ash, including its specific surface area ranging from 300 to 500 m²/kg and fine particle size, significantly affect its functionality in concrete mixtures. Its addition tends to improve workability, reduce water demand, and enhance long-term strength, while also impacting factors such as permeability and heat of hydration. The slower early strength gain is compensated by improved performance over time, showcasing the utility of fly ash in creating durable and sustainable concrete.