Durability effects of Silica Powder

The durability of concrete includes concrete's frost resistance, impermeability, chemical resistance, steel corrosion resistance and erosion resistance. I will only talk about its frost resistance, impermeability and chemical resistance to concrete. The erosive effect.
a) Frost resistance: When the amount of Silica Powder is small, the frost resistance of silica fume concrete is basically the same as that of ordinary concrete. When the amount of silica powder exceeds 15%, its frost resistance is poor. Through a large number of tests, this view has been basically confirmed. The main reason is that when the silica fume exceeds 15%, the expansion of the concrete increases, the relative dynamic elastic modulus decreases, and the compressive strength drops sharply. From the perspective of the internal characteristics of the concrete , The specific surface area is small, and the spacing coefficient is large.
b) Impermeability: Because Silica Powder particles are small, 20-100 times smaller than cement particles, they can be filled into the voids between cement particles to make concrete compact. At the same time, the secondary hydration of silica powder blocks new products. Permeation channels in concrete, so the impermeability of silica fume concrete is very strong, the permeability of concrete increases with the increase of water-binder ratio, this is because the compactness of water-cement is relatively poorer than that of concrete.
c) Chemical resistance: Mixing Silica Powder into concrete can reduce the content of Ca (OH) 2 and increase the compactness of concrete. It can effectively improve the corrosion ability of weak acid. However, it cannot be used in strong acid or high-depth weak acid. CSH decomposes in acid. In addition, it is also resistant to salt corrosion, especially to chlorides and sulfates. The reason why it is resistant to salt corrosion is that the silica fume concrete is denser and the pore structure is improved, thereby reducing The transmission speed of harmful ions is reduced and the formation of soluble Ca (OH) 2 and ettringite (3CaO·Al2O3·3CaSO4 ·32H2) is reduced, and the result of increasing hydrated calcium silicate crystals.