The cement ebook: your guide to cement & concrete

The use of air entrainment in concrete for freeze thaw protection has been known and used for more than hundred years.

The first time air was introduced into concrete it was an accident. During the time of the Romans, in order to keep the work site clean, food scraps would be thrown into the concrete mix. The Roman cement, much like cement today, produced a concrete with a high pH. In this alkaline environment the fat in the food scraps would be converted into soap and, during the mixing of the concrete, this soap would produce bubbles, becoming dispersed in the cement paste. This process is called the air entrainment of concrete.

With the fall of the Roman Empire, the art of concrete was lost. In 1756 John Smeation, a British engineer, rediscovered hydraulic cement and built the first concrete structure since the end of the Roman Empire. It was not until the early 1900's that air entrainment was rediscovered. This rediscovery was also an accident. During the manufacturing process fatty acid lubricants from nearby equipment leaked into the cement. The resulting cement was air entrained. The concrete made from this cement was found to be very durable in freeze thaw conditions and, as they say, the rest is history.

Modern day concrete is air entrained using not fat, but a soap that can produce a bubble of a given size in an alkaline environment. Most air-entrained concrete contains about 4 to 7 percent air by total volume of concrete. The percent of air in the concrete is determined by the amount of soap (air entraining agent) used and a number other factors. For example,the temperature of the concrete plays a very important role: as the temperature increases the percent of air will decrease and therefore, more air-entraining agent will have to be used. Also, air content increases as the slump increases, up to about 6 inches, and then decreases with further increased slump