Active silica is highly valued in civil construction because it is able to improve the properties of concrete when mixed with cement mortar. It is currently one of the most important substances for increasing the performance of concrete, helping to provide more strength, fluidity and durability to the material.
Because of this, it has been used in cement mortars for the most diverse applications, especially when dosing high-performance concrete - such as places that require high structural or abrasion resistance and in structures exposed to compromising conditions. However, its use is not restricted to these needs and, in general, it is considered a high quality product for various situations.
Thus, active silica is a relevant resource for any construction professional. With this in mind, we prepared this article to explain in depth what active silica is, why it is used and how it can be used in construction. Check out the following:
What is active silica?
Active silica, also known as Fume silica (silica smoke) or microsilica, is a mineral compound obtained as the result of a chemical process that occurs in the metallurgy industry. This substance is a residue from the manufacture of silicon iron or metallic silicon, a product used on a large scale in steelworks and metallurgy for the production of aluminum alloys, for example.
Because it is a waste by-product of a chemical process in the metallurgy industry, active silica has quite reasonable degrees of balance and stability in its physico-chemical constitution. By itself, active silica has no binding activity. However, when placed in the presence of water, this substance reacts with the calcium hydroxide produced by the reaction between cement and water present in the mortar, forming materials with binding properties. As a result, it enhances the strength of the concrete and closes its pores.
The appearance of active silica is that of a very fine powder, which is composed of extremely small particles, approximately 100 times smaller than cement grains. The high content of silica dioxide present in the substance, together with the high fineness of the material, makes it able to fill the “voids” between the concrete aggregates and its paste. These are precisely the characteristics that guarantee the excellent ability of active silica to react with the products resulting from its hardening.
Why use active silica in your construction?
Active silica is capable of reacting with the elements of the mortar and promoting different properties in concrete. Let's see below the main advantages that this substance promotes with its use:
Finish quality
The properties of silica in concrete mortar make it easy to achieve a quality finish. For this reason, it is highly recommended in architectural projects, works of art and any other structures that require greater sophistication in the result. Active silica reduces the appearance of cracks and cracks and reduces the porosity of the concrete, which guarantees a much more refined aesthetic pattern than the traditional one.
Reduction of concrete permeability
With the reduction of voids in the mortar and the appearance of cracks in the concrete, the final product becomes much less permeable than traditional concrete. By avoiding the infiltration of water and harmful agents, the interior of the concrete is much better protected against external conditions, preventing the manifestation of pathologies and the onset of problems.
Increase in concrete durability
The better adhesion of the mixture substrates makes the concrete much more durable. By preventing the passage of external agents into the concrete element, it gains a significant increase in protection against steel corrosion, chlorides, and carbonation. In this way, its lifespan is also extended.
Increased strength and performance
Active silica has the ability to give greater mechanical strength to concrete, in addition to elasticity and adhesion. It is possible to achieve resistances greater than 1000 Mpa using this material and, in addition to increasing the strength of concrete, it also acts to protect steel from corrosion.
Cost savings
By adding active silica to the mortar, it is possible to achieve the same strength with significant reductions in binder consumption - in this case, cement. Using between 5% and 8% of this substance in the mass, it becomes feasible to produce very high strength concrete with savings of at least 6% on the trace of the concrete, which translates into less expenditure on resources for mixing the mortar.
In addition, the increased strength of concrete allows structural elements with dimensions smaller than the usual ones to be used to withstand the same loads and stresses. Thus, active silica offers the possibility of creating lighter and more elegant structures, which also provides advantages in building design and in the reduction of material costs.
Improved workability
Workability is the ability of concrete to be handled and transported, making it easier for professionals to work with its application. It is, therefore, a fundamental factor especially when it comes to pumping the material to great heights or for its use in places that are difficult to execute.
Combating the RAA
The RAA, or alkali-aggregate reaction, is one of the biggest challenges faced in the use of concrete. This reaction occurs in concrete that has already hardened at a later age, and can cause pathologies such as cracking and the loss of strength of the concrete element. In studies conducted at the ABCP (Brazilian Portland Cement Association), it was attested that active silica is capable of inhibiting RAA in concrete pieces with efficiency and practicality, ensuring that the pieces have dimensional variations well below the maximum recommended by the ABNT.
Lower CO2 emissions and greater sustainability
The use of active silica helps to ensure that concrete production does not emit the same amounts of CO2 as the traditional process, reducing the environmental impact of the process. In addition, because it is a waste from the metallurgy industry, active silica helps the project to become more environmentally friendly because, otherwise, it is a product that would be destined for disposal in the environment if it were not reused as one of the components of the concrete mix.
Main applications of active silica
Active silica can be used in the most diverse concrete mortar applications. For the repair of structures, it guarantees more adhesion and protection to reformed concrete, making the element even more resistant to mechanical stress and chemical processes. It is also suitable for reinforced and prestressed concrete elements, increasing the strength of the concrete and making the structure more durable, increasing its protection against the elements and preventing its shrinkage during picking.
Likewise, active silica is a good addition to grouts, reducing the permeability of the mortar and combating the appearance of efflorescence and other pathologies caused by the presence of moisture. This substance can even be used for cement artifacts, where it increases the durability of the items and guarantees a better finish to the pieces, raising their aesthetic standard. Thus, its benefits can be used for any demand, providing a concrete of higher quality and performance in any situation.
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