Silica fume is a good concrete admixture, refractory additive, chemical product dispersant and metallurgical pellet binder for its excellent properties of high temperature resistance, prevention of segregation, corrosion and wear resistance. So, is there anything to note in the use of silica fume concrete? What are the specifications for silica fume concrete?

Silica fume concrete use specifications

There are many advantages of adding micro silica fume to concrete, which is the reason why micro-silica fume is popular in the concrete industry. However, to better play the combination of the two performance advantages, inseparable from the use of micro-silica powder specifications, the addition of silica fume in concrete is also a certain principle and standard, the following we will understand the specific specifications for the use of silica fume concrete. The amount of silica fume used is generally 5-10% of the amount of cementitious materials. Silica fume blending method is divided into internal and external blending.

1.Internal blending

In the premise of the same amount of water, 1 part of silica fume can replace 3-5 parts of cement (weight) and keep the compressive strength of concrete unchanged while improving other properties of concrete.

Internal blending is also divided into two kinds of equal substitution and partial equal substitution, equal substitution for the amount of silica powder instead of equal cement, partial substitution for 1 kg of silica powder instead of 1 to 3 kg of cement, as a study of the general dose of 5 % to 30 %, the water-cement ratio generally remains unchanged. The external admixture method refers to the silica powder like admixture in the concrete, and the amount of cement is not reduced, the amount of admixture is generally 5 % to 10 %, the general external admixture method and the mechanical properties of the concrete is much higher, but increased the amount of cementitious materials in the concrete.

2.External admixture

The amount of cement remains unchanged, and the addition of silica fume significantly improve the strength of concrete and other properties. Concrete mixed with silica fume when there is a certain slump loss. This point needs to be noted in the ratio test.

3.Adding order

In the silica fume concrete mixing silica fume should be added to the mixer immediately after the aggregates are fed.

There are two ways to join:

• put in the aggregate, followed by silica fume, cement dry mix, then add water and other admixtures.
• Put in coarse aggregate + 75% water + silica fume + 50% fine aggregate and mix for 15-30 seconds, then put in cement + admixture + 50% fine aggregate + 25% water and mix until uniform.

Mixing time is 20-25% or 50-60 seconds longer than ordinary concrete. Never add silica fume into the already mixed concrete.

Silica fume concrete use precautions

1. Because of the fine particles of silica fume, large specific surface area, high water demand, so when the concrete mixed with silica fume, must be used in combination with high-efficiency water reducing agent to achieve good results.
2. Silica fume into the concrete with the method of internal mixing and external mixing method. As the internal mixing method to reduce the amount of cement, so this method is generally used in the low strength grade of concrete; external infiltration method does not reduce the amount of cement, generally used in high strength grade of concrete.
3. The amount of silica fume in the concrete should not be too high or too low, the general dose of 5% to 10%, within this range of silica fume favorable role to play, that is, not only the role of silica fume instead of cement, a variety of good performance to give full play to, and can avoid the adverse effects, such as doping greater than 15%, the concrete frost resistance is reduced.
4. Due to the consistency of silica fume concrete, so in the design of concrete slump should be larger than the ordinary concrete 2 ~ 3cm. silica fume concrete mixing time should be extended than the ordinary concrete 0.5 ~ 1min, in order to make the concrete mix more uniform, to prevent silica fume in the concrete into a mass and cause quality accidents.
5. After the concrete is mixed with silica fume, the early maintenance must be strengthened to prevent the concrete from plastic shrinkage cracks.

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Henan Superior Abrasives specializes in producing special micro silica fume for resistant materials, building materials, rpc, insulation board, coatings, refractory castables, etc. We can provide different content and specifications of microsilica powder for different industries, welcome your inquiry and visit.