Air Entrainment

Air entrainment is added to concrete to provide freeze-thaw protection. If water inside the pores of the concrete freezes, the expansion of the water will create stress that can causing cracking and deterioration. The entrainment of many small air bubbles, spaced closely together, provides a means of relieving the stress from freezing water. Properly air entrained concrete can be very durable for many years, even in the most severe environments where there are many freeze-thaw cycles.

Optical image of air entrained concrete. [Photo by Paul Stutzman, NIST]

Entrained air voids in concrete. (Approx. 5mm Full Width) [Photo by Paul Stutzman, NIST]

Excess air and paste concentrations along aggregate with low air. [SEM by Paul Stutzman, NIST]

Polished section of Iowa Highway pavement showing entrained air void system. This image shows both entrained and entrapped air (by definition greater than 1.5 mm) (Approx. 10mm Full Width) [Photo by Paul Stutzman, NIST]

A closer view of same air system. Lighting at a low angle highlights the voids by shadowing. (Approx. 3mm Full Width) [Photo by Paul Stutzman, NIST]

Entrained air in masonry cement mortar. Air content in this system is about 20%. [SEM by H. Dale DeFord and David A. Lange, UIUC]