Entrained Air Void System in Concrete Structure and Pavements

Entraining air in concrete continues to challenge both specifiers and producers. On the one hand, concrete failures are still being reported due to inadequate air-void systems in transportation structures and pavements subjected to cyclic freezing and thawing in a saturated condition. On the other hand, low compressive strength resulting from excessive air content or excessively close spacing of air voids continues to occur. Both problems reflect the difficulties practitioners are having in achieving a consistent air-void system in in-place works. This is either due to variability in materials or practices, inadequate understanding of the differences in behavior of the various materials that can be used (i.e. air-entraining admixtures), or due to changes in the mixture during processing (i.e. after the batch has been tested and accepted). Furthermore, there is debate with regards to the amount of air and the required characteristics of the air-void system needed for frost resistance for modern concrete, with some questioning whether entrained air is needed at all in high performance mixtures.