Types of Mineral Admixtures

Today, we are going to discuss Fly Ash, which is a by-product of coal combustion in power plants. Can anyone tell me what it means for concrete?

Does it make concrete stronger?

Great question, Student_1! Fly Ash is actually pozzolanic, meaning it can react with calcium hydroxide in the presence of water to form additional calcium silicate hydrate, which strengthens the concrete. Remember this relationship; you can think of it as a key to unlock strength in your concrete mixes!

What types of Fly Ash are there?

There are two main types: Class F and Class C. Class F has low calcium oxide content and is used for applications requiring greater strength, while Class C has a higher calcium oxide content and can also be used in certain applications without Portland cement.

How much Fly Ash should we use?

Good inquiry! The typical dosage of Fly Ash is between 15 to 35% of the cement weight. Just remember the acronym C.A.R.E: Class (classification), Amount (dosage), Reactions (its pozzolanic properties), and Enhancement (strength improvement).

What are some applications for Fly Ash?

Excellent question! It’s commonly used in mass concrete structures, pavements, and reinforced concrete. This not only enhances the performance but also promotes a sustainable approach by recycling waste!

So to summarize, Fly Ash improves workability and long-term strength, and helps reduce heat of hydration.

Next up, let's talk about Silica Fume! Has anyone heard of this material before?

Isn't it some kind of dust from making silicon?

That's correct! Silica Fume is a by-product from the production of silicon and ferrosilicon alloys. This material is very fine and has a high surface area! Who can guess how that might affect its properties in concrete?

Does it make the concrete stronger?

Exactly! Its high pozzolanic activity not only increases strength but also reduces permeability drastically. Remember, when we think of Silica Fume, think of its ability to fill voids and improve density!

How much Silica Fume should be used?

Great question, Student_4! The recommended dosage is typically between 5 and 10% of the cement weight. What does that help decrease, any ideas?

Permeability?

Correct! This reduction in permeability means better durability in high-strength concrete and exposure to harsh environments.

So today, we discussed Silica Fume and its significant contributions: strength enhancement, improved durability, and low permeability.

Now, let’s turn our attention to Ground Granulated Blast Furnace Slag, often called GGBS. Who knows what sources it comes from?

Isn't it a by-product of iron production?

That's right! This slag is cooled rapidly with water to create a glassy material that can act as a latent hydraulic material. Can anyone tell me what ‘latent hydraulic material’ means?

It means it can react with water to contribute to strength, just like cement?

Exactly! GGBS can improve long-term durability under various environmental conditions. What dosage should we consider for using GGBS?

Isn't it 30-50%?

Yes, very good! GGBS can improve workability and lower the heat of hydration, making it ideal for large mass pours like those in marine environments.

To recap, GGBS enhances durability and contributes to strength while lowering hydration temperatures.