The production of ferrosilicon alloys or silicon metal produces silica fume as a byproduct. Concrete is one of the most useful applications for silica fume. It is a highly reactive pozzolan due to its physical and chemical characteristics.
Concrete with silica fume can be extremely strong and long-lasting. Silica fume is generally available from concrete admixture manufacturers and is added during the manufacturing process if specified. The concrete contractor must pay extra attention to the placement, finishing, and curing of silica-fume concrete.
Electric furnaces are used to make silicon metal and alloys. Quartz, coal, and woodchips are used as raw materials. Rather than being landfilled, the smoke produced by furnace operation will be collected and then traded as silica fume. This material’s most important application is a mineral additive in concrete.
Amorphous (non-crystalline) silicon dioxide is the main component of silica fume (SiO₂). Its individual particles are quite small, around 1/100th of the size of a typical cement particle. When used in concrete, silica fume is an extremely reactive pozzolan due to its small particles, huge surface area, and high SiO2 content.
For supporting vertical loads in any high-rise construction, high-strength concrete will be a very cost-effective material. 6,000 psi concrete generally was considered high strength before.
Concrete with a compressive strength of over 15,000 psi may now be easily made using silica fume. In the construction depicted to the right, silica-fume concrete having an indicated compressive strength of around 12,000 psi was utilized in columns that ran from the ground to the 57th story.
Bisley International which supplies various raw materials in the USA is also one of the well-known silica fume suppliers.
Physical properties of any silica fume material
- Silica fume particle diameter is between 0.1 microns and 0.2 microns.
- Its surface area is almost 30,000 m²/kg.
- Its density varies between 150 and 700 kg/m³.
Properties of fresh silica fume concrete
- To get similar workability to conventional concrete, silica fume concrete will need higher water content
- Low slump value
- Low workability
- The possibility of bleeding
- Segregation is low
- High plastic shrinkage
- The mixture can be cohesive
Properties of a hardened silica fume concrete
- As compared to ordinary concrete, the compressive strength of silica fume concrete will be higher
- Its modulus of elasticity will be substantially higher compared to ordinary concrete.
- Silica fume concrete creep is lesser compared to conventional concrete
Durability
- Silica fume concrete permeability is low, therefore, sulfate ions penetration is low.
- Corrosion resistance and abrasion resistance are high.
- In the paste matrix, the reaction of any silica fume having lime promotes durability. The lime reacts with a variety of chemicals, causing it to expand.
Advantages
- Silica fume can enhance the hardened and fresh concrete property
- Silica fume can reduce segregation and bleeding.
- The finishing process can be efficient because of low bleeding
- High durability
- High compressive strength
- High bond strength
- High flexural strength
- High modulus of elasticity
- Right for mass concreting as it can prevent thermally induced cracking.
Disadvantages
- Availability issue
- Higher cost
Applications
- High rise buildings
- Dam structure
- Parking structure
- Shotcrete rehabilitation
- Nuclear waste storages
