The byproduct of silicon metal is silica fume and it is spherical, sub-micron, amorphous silicon dioxide is commonly used in cement and concrete applications within the construction industry. Silica fumes have unique characteristics and many benefits have been observed so far by using them in construction.
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Technically, due to silica fume’s amorphous structure i.e., non-crystalline and its high specific surface area, it offers beneficial properties in diverse applications consisting of enhancing the sintering process and improving the high-temperature performance of refractory castables. The interaction between microsilica and other components in the refractory mix leads to significant improvements in overall performance.
By adding more water to the cement, the slurry of the cement gets thinner and weakens the cementing force. Then how to counter this effectively? This blog covers all the necessary points that will help you understand the importance of adding silica fume in concrete processes. Keep reading to know more.
Problems Leading to the Requirement of Silica Fume
Silica fumes are well-known to enhance the mechanical properties of cement. Following are the observed facts due to which silica fume demand has been significantly grown.
1. Concrete Strength:
Many times more water has been added to the concrete to obtain the desired fluidity. Due to the addition of extra water the cement slurry gets thinner resulting in weakening the cementing force. Also, the excessive water in the concrete forms water channels or blisters. When the concrete dries and the water evaporates, pores are left behind. This results in reducing the actual strength of the concrete and stress concentration occurs around the pores.
2. Concrete Cracking:
The concrete is highly prone to cracking due to shrinkage during curing and drying. In that case, silica fumes help address this problem by enhancing the microstructure of the concrete, which lowers the likelihood of cracks forming under stress.
3. Inadequate Early Strength Development:
Traditional concrete cement may not get the required strength levels quickly for certain applications like in precast or rapid construction cases. Adding silica fume to the concrete, accelerates strength gain, making it suitable for various construction projects required for early load-bearing capacity.
4. Environmental Concerns:
The high overuse of cement in concrete increases the emissions of carbon dioxide. In this case, silica fume serves as a supplementary cemental material which helps to reduce the total cement quantity. Thus, it maintains the proper strength, and durability and helps reduce the environmental impact.
5. Extra Water Requirement:
When micro-silica powder used in concrete is processed it needs more water to wet it. As the silica fume content goes above 5%, the water requirement for the same concrete consistency is boosted. If the water volume stays the same, more silica fume makes the concrete sticky. That’s where the silica fume requirement with a water-reducing agent is important to address to make the concrete more waterproof and strong without using extra water. This results in concrete with strong bonding that resists separation.
There are more problems associated with cement in concrete production, like low durability, workability challenges, corrosion risks, and more when it is used alone. That’s why silica fume enhances the impact on the concrete making it more durable and prolonging its life.
With the details of the above-mentioned complications, let us understand the process of adding silica fume in concrete to increase concrete’s positive properties.
Application of Silica Fume in Concrete
In order to understand how silica fume is used in concrete, it’s vital to first know the chemical reactions that take place when it is added to the concrete.
After adding silica fume to concrete for the first time, it remains inert. Afterward, once the water begins to react with the cement in the mixture, the primary chemical reaction starts to happen and that reaction creates two important chemical compounds which are as follows:
- Calcium Silicate Hydrate (CSH) – This is a crystalline compound accountable for the concrete’s strength after drying.
- Calcium Hydroxide (CH) – It is a by-product that serves as a filler and helps seal the pores within the concrete.
Eventually, a pozzolanic reaction takes place between Calcium Hydroxide and silica fume, forming extra Calcium Silicate Hydrate compounds that fill the gaps around the cement’s hydrated particles. Then, a denser structure in areas that would have otherwise been small voids, reduces the risk of infiltration due to these additional CSH compounds. As a result, the concrete gains enhanced flexibility, compressive, and bond strength.
The Effect of Incorporating Silica Fume into Concrete
Various effects are observed after adding silica fume to the concrete in construction processes. Some of the amazing effects are as follows:
1. Filling Effect
Through a huge number of experiments and estimates, it is observed that when 15% of cement is replaced with silica fume, the ratio of cement particles to the silica fume particles is 1/2000000, meaning there are a total two million silica fume particles for every one particle of cement. This proves that silica fume is highly influential in producing high-strength concrete for construction projects.
In high-strength concrete, silica fume fills the voids of cement particles because it is 100 times smaller than the diameter of cement particles. This increases the density of high-strength concrete and enhances its strength, which is the primary effect of silica fume.
2. Reduces Bleeding
In the case of high-strength concrete, silica fume incorporated into the cement paste significantly reduces the number of pores and enhances uniformity, while maintaining nearly the same porosity. Silica fume actually reduces the bleeding of high-strength concrete in the transition of cement slurry and aggregate interface leading to prevent moisture from accumulating under the aggregate, preventing moisture from collecting under the aggregate. Nevertheless, it makes the transition zone between the aggregate and cement paste more similar in structure, increasing the compactness of this zone and effectively reducing its thickness.
3. Boosts Strength
Silica fume particles act as ‘seeds’ for Ca(OH)2, resulting in making the crystals smaller and more randomly oriented. This helps in improving the bond between the aggregates and the cement paste, strengthening the connection between different components and giving the concrete the characteristics of a composite material.
Instead of just being an inert filler, the aggregate particles now help reinforce the concrete. Silica fume has a smaller effect on the strength of cement paste without aggregate, it greatly boosts the strength of concrete with the same water-to-binder ratio, making it stronger than plain paste.
4. Enhanced Durability:
By adding silica fume in concrete, the durability of the concrete increases due to a reduction of its permeability. This makes the concrete less susceptible to water ingress and chemical attacks, as a result protecting embedded steel reinforcement from corrosion.
5. Prevent Concrete Cancer
Concrete cancer is also popularly known as concrete spalling or concrete degradation. It is a state wherein concrete structures start to break down because of the corrosion of the steel reinforcement bars inside the concrete slab.
This is a particularly gradual and permanent issue that can compromise the structural integrity of bridges, tunnels, buildings, and other infrastructures. Silica fume plays a crucial role in addressing these effects on concrete cancer through various mechanisms.
By using silica fume in the concrete mixture the concrete’s durability, bond strength, and resistance to chemical attacks can be eliminated while reducing permeability which minimizes the ingress of water and corrosion.
What Makes Silica Fume Concrete Prone to Cracking?
In construction projects, Silica fume is often considered prone to cracking. This is all because silica fume concrete and its unique characteristics are not always fully understood, resulting in less quality control during construction, such as poor curing practices.
Another reason is that silica fume is generally used in concrete with high-performance requirements, such as achieving greater strength, lower permeability, and better durability. This type of concrete has a lower water-to-binder ratio and a higher content of cementitious material.
Incorporating silica fume in such cases contributes to early shrinkage, making the concrete often sensitive to cracking. Thus, under constrained situations, the overall early crack sensitivity is high.
Way to Prevent Cracking in Silica Fume Concrete
To prevent cracking in silica fume concrete, increase maintenance efforts to prevent early water loss and reduce the risk of plastic shrinkage cracks.
For high durability in standard strength concrete and self-compacting concrete, try to use combinations such as cement with fly ash and silica fume, cement with ground slag and silica fume, or cement with fly ash, ground slag, and silica fume can help maintain early crack sensitivity at a minimum.
In the construction industry, Sakshi Chem Sciences offers a variety of best-in-class construction chemicals under the brand name ADDAGE. Addage line of products has a great performance when it is used with a proper and wide range of materials. Let’s have a glance at it to know more.
Addage Micro Silica Powder (Fumecrete 90)
The Micro Silica Powder product is a dry-form silica powder formulated to improve the quality of concrete. It consists of extremely fine, solid, glass-like spheres composed of Silicon Dioxide (SiO2). It is popular to offer high strength to the concrete and reduce its water-binder ratio. Fumecrete 90 is beneficial to improve the bonding, flexural, and compressive strength & durability of the concrete.
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