Air Void System Requirements for Durable Paving Concrete - Another Look

The resistance of concrete to freeze-thaw (F-T) greatly depends on the characteristics of the concrete air-void system, such as the air content, size, and distribution. These air-void characteristics are influenced by every step of concrete production, from material selection and mixture proportioning to mixing, and placing. The research presented in this paper summarizes the observations from a comprehensive study that combined the in-situ performance of highway concrete with laboratory investigations. The field investigation involved determining the minimum requirements of air-void systems (AVS) for long-term durability against F-T cycles. In collaboration with several state agencies across the United States and Canada, core specimens were obtained for studying the properties of AVS resulting in different F-T conditions. Hardened air content, spacing factor, and specific surface of air-voids were determined for the extracted cores. The observations were supplemented by data obtained from a wide range of modern paving concrete mixtures. AVS characteristics were investigated using a variety of different techniques in fresh and hardened states. The main outcome of this research is a series of recommendations for minimum fresh and hardened AVS requirements to secure F-T durability.