Microsilica consists primarily of amorphous (non-crystalline) silicon dioxide (SiO2). The individual particles are extremely small, approximately 1/100th the size of an average cement particle. Because of its fine particles, large surface area, and the high SiO2 content, silica fume is a very reactive pozzolan when used in concrete. The quality of Microsilica is specified by ASTM C 1240.

High-strength concrete is a very economical material for carrying vertical loads in high-rise structures. Until a few years ago, 6,000 psi concrete was considered to be high strength. Today, using silica fume, concrete with compressive strength in excess of 15,000 psi can be readily produced. The structure shown at the above right used silica-fume concrete with a specified compressive strength of 12,000 psi in columns reaching from the ground through the 57th story.

The greatest cause of concrete deterioration is corrosion induced by deicing or marine salts. Microsilica concrete with a low water content is highly resistant to penetration by chloride ions. More and more transportation agencies are using microsilica in their concrete for construction of new bridges or rehabilitation of existing structures.

Microsilica concrete does not just happen. A specifier must make a conscious decision to include it in concrete to achieve desired concrete properties.

Microsilica for use in concrete is available in wet or dry forms. It is usually added during concrete production at a concrete plant. Microsilica-concrete has been successfully produced in both central-mix and dry-batch plants. Assistance is readily available on all aspects of handling microsilica and using it to produce consistent, high-quality concrete.

Microsilica concrete should be transported, placed, finished, and cured following the good concreting practices. Flatwork containing silica fume concrete generally requires less finishing effort than conventional concrete. finishing process in which the MIcrosilica concrete is placed, consolidated, and textured with little or no waiting time between operations. To gain the most benefits from using Microsilica, the concrete must be cured effectively.

microsilica