When concrete producers want to modify the properties of concrete, supplemental cementing materials (SCMs) can be used to achieve the intended goal. Silica fume is a very common SCM that is frequently used to increase the strength and durability of a concrete structure. Even though silica fume densifies concrete, it is not a waterproofer. Under hydrostatic pressure, other forms of waterproofing are required.

The use of silica fume in concrete shows a tendency for plastic shrinkage, drying shrinkage and cracking  resulting in water penetration and corrosion of reinforcing steel. This increased densification of the concrete often creates an illusion of waterproofing capability. In actuality, the use of silica fume may accelerate the deterioration process when cracking occurs.

Kryton’s Krystol Internal Membrane (KIM) admixture can work with silica fume. KIM decreases water demand, increases compressive strength, mitigates shrinkage cracking and provides permanent waterproofing. KIM reduces the common cracking effect of Silica Fume in concrete by:

• Reducing volume of bleeding per hour while increasing the hours in which bleeding occurs without allowing the surface area to dry prematurely due to evaporation.
• Lowering the heat of hydration resulting in a lower temperature during the concrete’s natural hydration process.

Due to the inherent nature of concrete, cracking can also be expected after the initial shrinkage has occurred. In more dense silica fume concrete the amount of cracking over a period of time is often greater. Water then penetrates through the cracks. This in turn leads to the corrosion of reinforcing steel and an accelerated deterioration of the concrete. KIM admixture’s ability to self-seal micro cracking is a distinct advantage. Even the most dense silica fume concrete cannot stop water penetration through micro-cracks. When a micro-crack occurs in a Silica Fume/KIM mix concrete, and water begins to penetrate the structure, KIM will immediately react with the un-hydrated cement particles and the water – causing crystals to grow throughout the crack. This will effectively seal the cracked area and protect the reinforcing steel from the corrosion process.

In instances where Silica Fume is required, KIM may be used to provide an excellent method of increasing concrete density, quality, compressive strength, appearance and structural life, while effectively reducing the limitations of Silica Fume.