What is the effect of adding silica fume to concrete?

What is the effect of adding silica fume to concrete?

Silica fume is added to Portland cement concrete to improve its properties, in particular its compressive strength, bond strength, and abrasion resistance.

Which of the following type of admixture will you recommend to avoid ill effects in cold weather concreting?

Accelerators. Accelerating admixtures can help offset the effects of low temperatures by increasing the rate of cement hydration. This aids in the concrete setting time and the development of early strength in the concrete.

How do you mix silica fume in concrete?

There are two ways to add silica fume: (1) Input aggregate, then put silica fume and cement dry mix, then add water and other additives. (2) Put coarse aggregate + 75% water + silica fume + 50% fine aggregate, stir for 15-30 seconds, then add cement + admixture + 50% fine aggregate + 25% water, stir until uniform.

Why is silica fume used in shotcrete?

Silica fume addition to shotcrete increases adhesion and cohesion. Consequently, the shotcrete building thickness attainable on overhead and vertical surfaces is substantially improved. Thickness to bond break (sloughing) and rebound loss were measured in a specially constructed rebound chamber.

How does Ggbs work in concrete?

Durability; GGBS reduces the likelihood of concrete thermal cracking, and it improves concrete’s resistance to damage from alkali-silica reaction, sulphates and chlorides. Concrete in aggressive environments is much more durable with the use of GGBS as a partial replacement for the cement.

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 can I add to concrete in cold weather?

Accelerators—Since colder weather leads to colder concrete, the set time can be delayed. Accelerators added to the concrete can keep it on schedule. Addition of 2% (by weight of cement) of calcium chloride is the traditional way to accelerate the hydration reaction—it is very effective and reasonably cheap.

How do you cure concrete in cold weather?

Make sure the concrete is maintaining a temperature of at least 40 degrees for its curing period. As active heating is discontinued, guard against the concrete cooling too rapidly. This can be done by gradually lowering the temperatures within an enclosure or by covering the concrete with insulating blankets.

How do you add 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 is silica fume a byproduct of?

silicon
Silica fume is a by-product from the production of elemental silicon or alloys containing silicon in electric arc furnaces. At a temperature of approximately 2000°C the reduction of high-purity quartz to silicon produces silicon dioxide vapor, which oxidizes and condenses at low temperatures to produce silica fume.

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.

When to add silica fume to concrete mix?

Strict accordance with the ratio of construction. During silica fume concrete mixing, silica fume should be added to the blender immediately after aggregate feeding. (1) Input aggregate, then put silica fume and cement dry mix, then add water and other additives.

What kind of fume is used in concrete?

Because of its fine particles, large surface area, and the high SiO2 content, silica fume is a very reactive pozzolan when used in concrete. The quality of silica fume is specified by ASTM C 1240 and AASHTO M 307.

Which is better silica fume or Portland cement?

Silica fume’s benefits are already evident in the fresh concrete state before it begins to harden. Its small particle size which is 100 times finer than ordinary portland cement complements the finess modulus of concrete and provides a ball-bearing effect, which improves thixotropic behavior,…

What are the raw materials for silica fume?

The raw materials are quartz, coal, and woodchips. The smoke that results from furnace operation is collected and sold as silica fume, rather than being landfilled. Perhaps the most important use of this material is as a mineral admixture in concrete. Silica fume consists primarily of amorphous (non-crystalline) silicon dioxide (SiO2).