Ordinary Portland Cement is amongst the category of the most widely & commonly used cement in the building process. The use of admixtures is beneficial for better quality of the concrete.
Silica fume is one of the kinds of admixture which is widely used in construction.
The Silica fume acts as a filler as it has very tiny particles which are far tinier than cement due to which the admixture helps in filling the pores of the concrete. This mineral is mostly a recycled compound admixture in high-strength and high-performance concrete.
Concrete is basically a mixture of cement, water, sand, and aggregates. The slab of the building, pillars of the building/bridges, and foundation of the structure are all made up of concrete.
Concrete is a very strong and versatile material. The cement and water act as a gel along with the aggregates and sand. Once the cement concrete mixes with the chemicals it stabilizes & forms quandaries with the water. The initial hardening of the concrete happens within a few hours.
The concrete used with the admixtures can have a long-term effect on the structure as it remains strong and can be long-lasting. Concrete used for the the slab creates a rigid surface, resulting in soil erosion, water effluence, and disaster.
When the building is being demolished then in that case the particles which flow from the concrete lead to pollution in the air. The Silica Fume has consequences of siliceous metallic or ferrosilicon blends. Silica fume helps in higher durability of the concrete. Silica fumes are frequently also referred to as micro-silica.
Compared with cement particles, the silica admixture particles are 100 times smaller. As a result, this admixture helps fill in the spaces and pores of the cement. This substance is a most unstable pozzolana which utilizes concrete.
Effects of silica fume in concrete:
Physical effect – The occurrence of smaller elements can increase concrete properties. These consequences are known as particle filling or micro filling.
Chemical effect – Silica Fume is basically an active pozzolanic solid material. A material having siliceous and aluminous properties that also possesses less or no cementitious significance but exceptionally split practice and within the occurrence of moistness which chemically reacted by calcium hydroxyl at normal temperatures to make complexes containing cementitious properties.
Properties of Silica Fume
There are three types of properties for Silica Fume:
- Physical properties
- Chemical properties
- Mechanical properties
Description of the properties is as follows:
Physical properties:
- Particle size: Silica particles are of very low dimension, and they are nearly a scale of one hundred times less in size when compared to cement. These particles help in filling the pores of the concrete.
- Specific surface area: The specific surface area of silica fume is very high. It has greater reactivity and can react more effectively with other materials.
- Bulk density: The bulk density of silica is quite low. The low density of the material can affect the handling and transportation which may require special considerations in its use.
- Color: The admixture has grey in color particles.
Mechanical properties:
- Compressive strength: Silica Fumes increase the compressive strength of the cement in the concrete.
- Durability: The durability increases, and the permeability of the concrete gets reduced using material. The Silica material is beneficial to be used in concrete, especially during harsh weather conditions like bridges, marine structures, and industrial floors.
- Abrasion Resistance: The abrasion resistance of the concrete is improved wherein high wear and tear happens. It is beneficial for heavy-duty flooring.
- Flexural strength: The flexural strength is improved of the concrete making it resistant to bending forces.
Chemical properties:
- Silicon Dioxide (SiO2) Content: This admixture consists of 85% silicon dioxide (SiO2), which is a primary active ingredient. This admixture is responsible for the pozzolanic reaction which is a chemical reaction that happens when the material is mixed with the concrete.
- Amorphous structure: The crystalline silica is amorphous; that is, it lacks a regular structure. It is reactive which is beneficial for pozzolanic reaction in concrete.
- Pozzolanic activity: The admixture reacts with calcium hydroxide which holds concrete together and acts as a glue. Thus the durability is improved.
Advantages of Silica Fume in concrete:
- Stronger bonds were formed between the aggregates that make up concrete and the stickiness material that surrounds combined substance resulting in improved strength.
- It reduces the effect of permeability due to which the chloride ions and water do not penetrate.
- This, in essence, will reduce the volume of expansion of the concrete because of alkali-silica reactivity.
- Electrical resistivity is higher than 100 times more than that of plain concrete without admixtures.
- The compound increases the abrasion resistance of floors, roofs, deck slabs, and aquatic structures.
- The compound increases the biological occurrence of nitrites, chlorides, acids, and sulfides.
- Silica fume concrete to produce compressive strengths of 20,000 psi under job site circumstances.
- The combined body improved flexural strength and toughness.
- Either in a wet form or a dry form, this material is capable of being used as concrete
- It requires less ruining effort as compared to traditional concrete.
Disadvantages of Silica Fume:
- It is not easily available.
- It is a slightly costly material as compared to fly ash.
- It reduces the slurry volume.
- This material increases the water demand.
- It increases the viscosity and slurry density.
Micro Silica Fume Percentage in Concrete:
Whenever there is a higher presence of silicon oxide, the higher the percentage of micro silica in concrete. Generally, inside the concrete the silicon oxide should be present more than 85%. The carbon silica fume absorbs the air-entraining agents in concrete thus the loss of ignition required should be less than 7%.
The quantity of micro silica added to the concrete should not be excessively high or excessively low. It should be 5-10% of the concrete mixture. If the dosage is used more than 15% of the concrete mixture, then the cold resistance of the concrete gets reduced.
Can Silica fume be used as a replacement for cement?
If the Silica fume is used as a concrete the functioning is very much like fly ash. By reducing the hydration heat and improving resistance towards corrosion, freeze-thaw cycles, and permeability, this compound may improve the concrete blend’s fluidity.
Alkali-aggregate reaction is inhibited by this subject because its effect is greater than that of fly ash. Silicon reacts with calcium, oxygen, and hydrogen to form hydrated calcium silicate.
The use of silica fumes in concrete is just in the range of 5-15%, the cement slurry becomes viscous if the concentration exceeds 20%. This compound, therefore, increases the consumption of water.
This improved compound enhances concrete pumping performance and resists more vibrations without segregation. The compound also helps in improving the fluidity of the concrete.
Using the pouring compound method Silica Fume concrete can have a slump of 500 PX higher than ordinary concrete. It is highly probable that this substance will cause fractures in the cement, which is why a lot of care must be directed towards the curing chemical for concrete.
Silica Fume compound which is known as high strength concrete or else ultra-high strength concrete, high permeable concrete, underwater high dispersion concrete. Etc.
Product by Sakshi Chem Sciences Pvt Ltd:
The product Silica Fume is known as Fumecrete 90 which is manufactured by Sakshi Chem Sciences Pvt Ltd. It is possible to enhance the concrete flexural bond strength with the help of this compound.
The product also reduces corrosion in concrete and improves the life of the concrete to make it a long-lasting structure. Improvement in concrete quality can be attained by reducing the alkali-silica reaction.
The particles of micro silica are crystalline substances that are easy to dissolve in concrete and thus also fill the pores and gaps inside the concrete. The particles are 100 times smaller than cement powder.
The Fumecrete 90 reduces the water binder ratio, and dispersion of concrete.
Conclusion:
Thus, we can conclude that silica fumes can be used in concrete as an admixture with 5-15% of the mixture. The quantity of the compound being used should not be too high nor it should be excessively low.
The mixture will fill up the gaps between the pores of the concrete. Therefore, it is highly recommended to use Silicone Fume inside the concrete as this will help improve the quality of the concrete.
The effect of permeability is reduced due to which the chloride ions do not penetrate. The only care should be taken that the cracks may get formed inside the concrete due to the use of this material. So, the material should be used carefully in the concrete.