RCPT tested micro silica fume, also known as silica fume or microsilica, is a byproduct of the production of silicon metal and ferrosilicon alloys. It is a highly reactive, fine-grain powder that consists of very small particles of silicon dioxide, with an average particle size of less than 1 micron. Silica fume is added to concrete mixes to improve the strength, durability, and resistance to corrosion. It is also used in other applications, such as refractory materials and high-performance coatings.