Micro silica fume, also known as silica fume, is a by - product of the silicon and ferrosilicon alloy production in electric arc furnaces. It is a very fine powder with high pozzolanic activity. In recent years, there has been a growing interest in its use in shotcrete applications. As a micro silica fume supplier, I am often asked whether micro silica fume can be effectively used in shotcrete, and in this blog, I will delve into this topic in detail.
Properties of Micro Silica Fume
Before discussing its application in shotcrete, it's important to understand the properties of micro silica fume. Micro silica fume consists of extremely fine spherical particles, with an average particle size of about 0.1 - 0.2 micrometers, which is much smaller than that of cement particles. This fine particle size gives it a large specific surface area, typically ranging from 15,000 to 30,000 square meters per kilogram.
The high pozzolanic activity of micro silica fume is another key property. When mixed with water and calcium hydroxide (a by - product of cement hydration), it reacts to form additional calcium silicate hydrate (C - S - H) gel, which is the main binding phase in concrete. This reaction not only enhances the strength of the concrete but also improves its durability.
Advantages of Using Micro Silica Fume in Shotcrete
1. Improved Adhesion
One of the main challenges in shotcrete applications is achieving good adhesion to the substrate. Micro silica fume can significantly improve the adhesion of shotcrete. The fine particles of micro silica fume fill the voids between the cement particles, creating a denser and more cohesive matrix. This increased cohesion allows the shotcrete to better adhere to the surface, reducing the rebound rate. Rebound is the material that bounces off the surface during the spraying process, and a high rebound rate leads to material waste and increased costs. By using micro silica fume, the rebound rate can be reduced from 20 - 30% to as low as 5 - 10%.
2. Enhanced Strength
The pozzolanic reaction of micro silica fume contributes to the early and long - term strength development of shotcrete. In the early stages, the formation of additional C - S - H gel fills the pores in the concrete, increasing its density and strength. In the long - term, the continued reaction of micro silica fume with calcium hydroxide further enhances the strength of the shotcrete. Studies have shown that shotcrete containing micro silica fume can have up to 30 - 50% higher compressive strength compared to plain shotcrete at 28 days.
3. Improved Durability
Micro silica fume improves the durability of shotcrete in several ways. Firstly, the denser matrix formed by the addition of micro silica fume reduces the permeability of the shotcrete. This means that it is more resistant to the ingress of water, chloride ions, and other harmful substances. Chloride ingress can lead to corrosion of steel reinforcement in shotcrete, which can significantly reduce the service life of the structure. By reducing permeability, micro silica fume helps to protect the reinforcement and extend the durability of the shotcrete.
Secondly, micro silica fume can improve the resistance of shotcrete to chemical attack. For example, it can enhance the resistance to sulfate attack, which is a common problem in concrete structures exposed to sulfate - rich environments such as soil or groundwater.
Applications of Micro Silica Fume in Different Shotcrete Types
1. Wet - Mix Shotcrete
In wet - mix shotcrete, all the ingredients, including cement, aggregates, water, and admixtures, are mixed in a mixer before being pumped to the spraying nozzle. Micro silica fume can be easily incorporated into the wet - mix process. It helps to improve the workability of the wet - mix shotcrete, making it easier to pump and spray. The improved adhesion and strength properties also make wet - mix shotcrete with micro silica fume suitable for a wide range of applications, such as tunnel linings, slope stabilization, and swimming pool construction.
2. Dry - Mix Shotcrete
In dry - mix shotcrete, the dry ingredients are conveyed through a hose to the spraying nozzle, where water is added just before spraying. Micro silica fume can also be used in dry - mix shotcrete. It can be pre - blended with the dry ingredients or added at the nozzle. The addition of micro silica fume in dry - mix shotcrete reduces the rebound rate and improves the quality of the sprayed material. Dry - mix shotcrete with micro silica fume is often used in applications where a high - strength and durable lining is required, such as in mines and underground structures.
Challenges and Considerations
While micro silica fume offers many advantages in shotcrete applications, there are also some challenges and considerations.
1. Dosage
Determining the appropriate dosage of micro silica fume is crucial. Too little micro silica fume may not achieve the desired improvements in adhesion, strength, and durability, while too much can lead to increased water demand and potential workability issues. Generally, the dosage of micro silica fume in shotcrete ranges from 5 - 15% by weight of cement.
2. Mixing
Proper mixing is essential to ensure the uniform distribution of micro silica fume in the shotcrete. Inadequate mixing can result in localized areas with high or low concentrations of micro silica fume, which can affect the performance of the shotcrete. Special mixing equipment may be required to ensure thorough mixing, especially when dealing with large - scale applications.
3. Cost
Micro silica fume is more expensive than ordinary cement. However, the benefits of using micro silica fume, such as reduced rebound, improved strength, and enhanced durability, can offset the additional cost in the long run. When considering the overall cost - effectiveness, factors such as material waste reduction, reduced maintenance costs, and extended service life should be taken into account.
Our Micro Silica Fume Products
As a micro silica fume supplier, we offer a range of high - quality micro silica fume products. Our Condensed Silica Fume is a highly concentrated form of micro silica fume, which is suitable for applications where a high pozzolanic activity is required. Our Silica Fume for Chemical Use is specifically designed for chemical industries, where its unique properties can be utilized in various chemical processes. We also provide Refractory Silica Fume, which is ideal for refractory applications, offering excellent heat resistance and strength.
Conclusion
Micro silica fume can be effectively used in shotcrete applications. It offers significant advantages in terms of improved adhesion, enhanced strength, and better durability. While there are some challenges and considerations, proper dosage, mixing, and cost - benefit analysis can help to overcome these issues. If you are involved in shotcrete projects or other applications where micro silica fume can be beneficial, we invite you to contact us for more information and to discuss your specific requirements. We are committed to providing high - quality micro silica fume products and professional technical support to help you achieve the best results in your projects.
References
- Mehta, P. K., & Monteiro, P. J. M. (2014). Concrete: Microstructure, Properties, and Materials. McGraw - Hill Education.
- ACI Committee 506. (2010). Guide to Shotcrete. American Concrete Institute.
- Neville, A. M. (1995). Properties of Concrete. Pearson Education.