Microsilica powder, also known as silica fume or condensed silica fume, is a by-product of the production of silicon metal and ferrosilicon alloys. It is a very fine, powdery material that consists of spherical particles with an average diameter of less than 1 micron. Microsilica powder is commonly used in concrete and other construction materials for its unique properties. Here are some of the main roles of microsilica powder:

1. Enhancing concrete strength and durability: Microsilica powder is used as a pozzolanic admixture in concrete to improve its strength, durability, and resistance to chemical attack. The silica fume particles react with calcium hydroxide in the cement to form additional cementitious compounds, which results in a denser, stronger, and more durable concrete.

2. Reducing permeability and increasing impermeability: Microsilica powder helps to reduce the permeability of concrete by filling in the spaces between the cement particles and reducing the size of the capillary pores. This results in a more impermeable concrete that is less susceptible to water and chemical penetration.

3. Improving workability and pumpability: The addition of microsilica powder to concrete can improve its workability and pumpability, making it easier to handle and place. This is due to the fine particle size of the silica fume, which reduces the amount of water needed to achieve a desired workability.

4. Reducing bleeding and segregation: Microsilica powder helps to reduce bleeding and segregation in concrete by filling in the spaces between the cement particles and increasing the viscosity of the mix. This results in a more uniform and consistent concrete that is less prone to bleeding and segregation.