Polished concrete with air entrainment

Air-entrainment is generally used in exterior environments where freeze-thaw events are present. Air-entrainment significantly increases durability against freezing by creating millions of microscopic, protective air bubbles (typically 4-7% total volume), resulting in a more porous, less reflective, and less dense surface. It is notoriously difficult to polish. Air-entrainment was discovered accidentally in the 1930s.