What does silica fume do to concrete?

What does silica fume do to concrete?

Silica fume is added to Portland cement concrete to improve its properties, in particular its compressive strength, bond strength, and abrasion resistance. Silica fume also blocks the pores in the fresh concrete so water within the concrete is not allowed to come to the surface.

How does silica fume behave in a concrete mixture?

Researchers generally agree that silica fume reacts with portland cement concrete in two ways: by altering the hydration reaction, and by the “microfiller effect.” When water is added to portland cement, hydration occurs, form- ing two primary products.

How does silica fume improve concrete strength?

A reduction in water-binder ratio (from 0.35 to 0.30) increased the ability of the concrete to resist chloride ion’s penetration. The introduction of silica fume in concrete reduced the water absorption capacity of concrete. A change in water-binder ratio also dramatically reduced the water absorption of concrete.

What is the difference between fly ash and silica fume?

Silica Fume is typically much more reactive, particularly at early ages , because of its higher silicon dioxide content and because of its very small particle size. Disadvantages of Fly Ash: – High-carbon fly ash materials tend to use more water and darken the concrete as well.

What are the disadvantages of high silica cement?

disadvantages of silica fume in concrete

• Silica fume concrete is too viscous and difficult to apply.it is not easy to wipe the surface.
• Silica fume requires a high amount of water and needs to be used with a superplasticizer.
• The price of silica fume is relatively high compared to cement and fly ash.

Is silica still used in concrete?

Concrete and masonry products contain silica sand. Since concrete and masonry are primary building materials, there are numerous ways for construction workers to be exposed. TT 1 Abrasive blasting using silica sand as the abrasive.

Is silica fume toxic?

Repeated exposure can damage the eyes. * High exposure to Silica, Amorphous (Fume) can cause a flu-like illness with headache, fever, chills, aches, chest tightness and cough. * Repeated exposure to Silica, Amorphous (Fume) can cause lung damage (fibrosis).

What is fly ash in cement?

Fly ash is a pozzolan, a substance containing aluminous and siliceous material that forms cement in the presence of water. When used in concrete mixes, fly ash improves the strength and segregation of the concrete and makes it easier to pump.

How do you make silica fume?

1. Add cement and fly ash or slag cement, if being used,
2. Mix 11⁄2 minutes.
3. Place 75% of water in mixer*
4. Add coarse aggregate.
5. Add silica fume slowly into the revolving mixer.
6. Mix 11⁄2 minutes.
7. Add fine aggregate.
8. Wash-in all ingredients using the remaining 25% of water.

What are the advantages of using fly ash in concrete?

Fly ash use in concrete improves the workability of plastic concrete, and the strength and durability of hardened concrete. Fly ash use is also cost effective. When fly ash is added to concrete, the amount of portland cement may be reduced. Benefits to Fresh Concrete.

Which of the following grades is not ordinary concrete?

Ordinary concrete grades include grades of M10, M15, and M20. Standard grades include M25, M30, M35, M40, M45, M50, and M55. High strength concrete grades include greater than M60. Hence, M40 grade of concrete is not used as ordinary concrete.

How much silica does it take to get silicosis?

Because silicosis is caused by cumulative or repeated exposure to respirable crystalline silica, it makes sense that we would want to limit exposure as much as possible! OSHA has set the Personal Exposure Limit (PEL) at 50 micrograms per cubic meter of air, averaged over an 8 hour shift.

Where can I get silica fume for concrete?

Silica fume is available from suppliers of concrete admixtures and, when specified, is simply added during concrete production. Placing, finishing, and curing silica-fume concrete require special attention on the part of the concrete contractor. Silicon metal and alloys are produced in electric furnaces as shown in this photo.

What do you need to know about silica fume?

The mechanism, physical characteristics, benefits, and production aspects of concrete made with silica fume are described. Recommendations are given for measuring, mixing, handling, transporting, placing, finishing, and curing concrete with silica fume additives. CONTENTS

What is the compressive strength of silica fume concrete?

Today, using silica fume, concrete with compressive strength in excess of 15,000 psi can be readily produced. The structure shown at the above right used silica-fume concrete with a specified compressive strength of 12,000 psi in columns reaching from the ground through the 57th story.

What kind of fume is used in concrete?

Silica fume that is used in concrete typically has an Si02 content in excess of 85 percent, while fly ashes typically have an Si02 content of 30 to 60 percent.