Silica fume advantages and disadvantages in concrete

Silica fume advantages and disadvantages in concrete

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Advantages of silica fume in concrete:

(1) Silica fume is a kind of neutral inorganic filler with very stable physical and chemical properties. It does not contain crystalline water, does not participate in the curing reaction, and does not affect the reaction mechanism.

(2) Good infiltration for various kinds of resin, good adsorption performance, easy to mix, no agglomeration phenomenon.

(3) The size distribution of silica fume is reasonable, strong densification, large hardness and wear resistance. It can greatly improve the tensile strength, compressive strength, impact strength, and wear resistance of the cured products, and the abrasion resistance can be increased 0.5 – 2.5 times.

(4) It can increase the thermal conductivity, change the adhesive viscosity and increase the flame retardancy.

(5) The exothermic peak temperature of curing reaction of epoxy resin can be reduced, the linear expansion coefficient of solidified products and the shrinkage rate of solidified products can be reduced, so as to eliminate internal stress and prevent cracking.

(6) Due to the fine grain size and reasonable distribution of silica fume, it can effectively reduce and eliminate precipitation and stratification.

(7) Pure silicon powder, low content of impurities, stable physical and chemical properties, so that the curing material has good insulation properties and arc resistance.

(8) The chemical composition of silica fume is silica (SiO2), which belongs to inert material. It doesn’t react with most acids or alkaloids. The silicon powder is evenly distributed and covered on the surface of objects. It has strong corrosion resistance and cavitation resistance increased 3-16 times.

(9) Small bulk density, 0.2 – 0.8, or 1 – 2.2. As polymer filling material, it can reduce the cost of the product by reducing the amount of loading and saving the amount of polymer.

(10) Frost resistance is good, and the relative elastic modulus of micro silica fume is 10 to 20% after 300-500 fast freeze-thaw cycles, while the average elastic modulus of ordinary concrete is 30 to 73% after 25-50 cycles. Therefore, the frost resistance of concrete can be improved.

(11) Early strength, microsilica concrete can shorten the induction period and have the characteristics of early strength.

Disadvantages of silica fume in concrete

1. Dry shrinkage.

Silica fume concrete shrinkage rate is large, especially early dry shrinkage, easy to make crack in the application of silica fume concrete, affect the overall strength and using effect. For example, after construction, strengthening water and sprinkler maintenance can decrease this problem, but the cracks are still unavoidable in many construction projects.

2. The construction is difficult.

The workability of concrete is an important parameter in the design of concrete mix proportion, silica fume concrete workability is poor, is not easy to make the concrete vibrating close grained, not easy to plaster, influencing the smoothness of concrete quality and uniformity of the surface.

3. It is easy to produce temperature cracks.

Concrete with silica fume early strength develop quickly, the corresponding concrete hydration heat dissipation quickly, resulting to rise concrete hydration heat temperature, easy to produce high temperature stress in the concrete, the stress concentration in the top of the dry shrinkage crack, make dry shrinkage crack extend even through the formation of transfixion cracks.

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Advantages And Disadvantages Of Silica Fume In Concrete

Silica fume, or microsilica, is a significant by-product of the ferrosilicon and silicon metal alloy manufacturing process. It has broad applications in concrete, providing essential benefits for industries such as marine, building construction, and oil and gas globally.

At HSA, China's leading provider of silica fume, we thoroughly understand silica fume applications. Today, let’s delve into the benefits and drawbacks of using silica fume in concrete.

What is Silica Fume?

Before examining the advantages and disadvantages of silica fume in concrete, let’s briefly review what silica fume is.

Silica fume, also known as microsilica, is a pozzolanic material similar to fly ash or Portland cement. It consists of non-crystalline or amorphous Silicon Dioxide (SiO2) with particles 100 times smaller than standard cement particles. The fume particles measure less than 1 micron in diameter, forming a superfine powder with a density of 2.2 g/cm3.

Silica fume is categorized into densified and undensified:

• Undensified silica fume has a bulk density of 200-350 kg/m3.
• Densified silica fume has a bulk density of 380-750 kg/m3.

Adding silica fume during batching can enhance concrete’s strength and durability.

Why is Silica Fume Important?

As a fine powder, silica fume is pivotal in manufacturing refractories and concrete. In concrete, it enhances mechanical properties, achieves superior corrosion strength, increases sulfate resistance, and improves abrasion resistance. Furthermore, it reduces the mixture's permeability, boosting durability.

Silica fume is used in virtually all grades of concrete, improving the strength and high-temperature performance of refractories. It's also utilized in the rubber and water glass industries.

How is Silica Fume Used in Concrete?

To understand silica fume’s pros and cons, it’s crucial to know the chemical reactions it triggers in concrete.

Initially, silica fume remains inert when added to concrete. As the water reacts with Portland cement (hydrating), it produces two key compounds:

• Calcium Silicate Hydrate (CSH): Provides material strength.
• Calcium Hydroxide (CH): A by-product that fills pores within the concrete.

Next, a pozzolanic reaction occurs between Calcium Hydroxide and silica fume, producing additional Calcium Silicate Hydrate that fills voids around the cement particles. This densifies the concrete matrix, improving flexural, compressive, and bond-strength properties.

For more 90% Undensified Silica Fume information, please contact us. We will provide professional answers.

Important Advantages of Silica Fume

Due to its properties, silica fume is extensively used where increased concrete strength and durability are required. Suppliers like Henan Superior Abrasives Import & Export Co., Ltd provide silica fume, which can be added during concrete production to enhance fresh and hardened concrete characteristics.

Here are some key advantages of silica fume:

1. Very Stable Chemical and Physical Properties

Silica fume acts as a neutral filler with exceptionally stable chemical and physical properties. It does not contain crystalline water, participate in curing reactions, or affect the reaction mechanism.

2. Increased Thermal Conductivity

Silica fume boosts thermal conductivity, improves flame retardance, and modifies adhesive velocity.

3. Good Adsorption Performance

Silica fume exhibits excellent adsorption performance and infiltration for various resins. It mixes well and shows no aggregation.

4. Reduced Precipitation and Stratification

Its fine grain size and reasonable distribution help eliminate stratification and reduce precipitation.

5. Improved Strength

The size distribution ensures good hardness, densification, and wear resistance. Silica fume enhances wear resistance, compressive, and tensile strength of cured products. Abrasion resistance can improve by 0.5-2.5 times.

6. Improved Insulation

Made of pure silicon powder with low impurities, silica fume possesses stable properties that provide good arc resistance and insulation for the curing material.

7. Reduced Overall Costs

With bulk density ranging between 0.2-0.8 or 1.0-2.2, using silica fume as a polymer filling material can lower product costs by reducing polymer usage and the amount of loading.

8. Improved Corrosion Resistance

Silica fume, made of inert SiO2, does not react with most acids or alkaloids, offering cavitation resistance and corrosion resistance by 3-16 times.

9. Shortened Induction Period

Adding silica fume shortens the induction period and provides early strength.

10. Crack Prevention

Silica fume lowers the peak temperature during epoxy resin's curing reaction, reduces shrinkage rate, and decreases the linear expansion coefficient, reducing internal stress and preventing cracking.

11. Improved Frost Resistance

Microsilica maintains a relative elastic modulus of only 10-20% after 300-500 freeze-thaw cycles. In contrast, ordinary concrete's modulus drops 30-73% after 25-50 cycles. Thus, microsilica significantly boosts concrete's frost resistance.

Disadvantages of Silica Fume in Concrete

While silica fume offers numerous benefits, it also has some drawbacks:

1. Difficulty of Construction

Concrete workability is crucial in mixture design. Excessive silica fume can reduce constructability, making concrete harder to plaster and less uniform, affecting overall quality.

2. Dry Shrinkage

Silica fume concrete exhibits higher shrinkage rates, especially early dry shrinkage. The filling effect reduces moisture, causing cracks and affecting overall strength. High external temperatures increase surface water evaporation, exacerbating shrinkage cracks. Maintenance practices like strengthening water and sprinkler procedures can mitigate this issue.

3. Temperature Cracks

Microsilica concrete tends to develop temperature cracks due to quick hydration heat dissipation, increasing concrete temperature and inducing high-temperature stress, which can deepen existing cracks into transfixion cracks.

4. High Price

Microsilica is more expensive than fly ash or cement. However, the superior performance of silica fume cement justifies the higher initial cost in the long term.

Shop for High-Quality Silica Fume at HSA

While silica fume has both advantages and disadvantages, it remains an essential material with widespread applications in construction, marine, and oil and gas industries.

To leverage the benefits while mitigating the challenges, choose a reliable silica fume supplier like Henan Superior Abrasives Import & Export Co., Ltd. Shop high-quality silica fume products today.

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