Frost and De-icing Salts

Air entrainment generally improves durability by reducing permeability. The resistance of hardened concrete to the action of frost and de-icing salts is considerably improved by the use of air-entraining admixtures. This is-achieved by the entrained-air bubbles acting as expansion chambers to accommodate the ice formed within the capillaries. Because the bubbles break up the continuity of the capillaries they also reduce permeability and water adsorption. 

The major use of air-entraining admixtures is in the production of concrete pavings for roads and airfields where improved resistance to frost and de-icing salts is required. The Department of Transport specification for Road and Bridge Works specifies 4 /2% 114% air entrainment for the top 50 mm of pavement quality concrete. 

The incorporation of entrained air into a mix enables the concrete to withstand better the action of frost and de-icing salts. The use of air-entraining admixture also improves workability. 

In spite of the decades of use of air-entraining agents (AEA) for the improvement of frost resistance of concrete, there has been a significant increase in reported cases of poor performance of concrete exposed to freezing and thawing, particularly where de-icing salts are used. Examination of specimens from a large number of concrete structures showed that only about half of the structures had an air-void system (AVS) that met the... 

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