Strength Enhancement
Concrete strength is typically enhanced through the use of compounds consisting of microsilica (also known as silica fume), which when added to the mix, create a significant increase in compressive and flexural (bending) strength in concrete, as well as a reduction in its permeability. An example of an application for high strength concrete is in lower-level building columns in tall structures, which are under extremely heavy loads and require concrete compressive strengths and values of up to 20,000 pounds per square inch. For comparison, most standard concrete is mixed to provide compressive strengths of 3,000 to 4,000 pounds per square inch.
Air-Entraining Admixtures
The introduction of air into a concrete mix can provide extensive protection against freezing, by creating an internal buffer within the concrete that allows it to contract without immediately resulting in breakage. To create the addition of tiny air bubbles to the concrete, a surfactant (detergent) is incorporated into the concrete prior to mixing. The mixing process generates the bubbles, most of which remain in the concrete as it hardens and become part of the final structure.