It is common practice to purposely trap small air-voids in concrete in order to give it frost resistance. A large number of factors have been recognized to impact the ability to entrain and stabilize these microscopic air-voids in concrete. This dissertation investigates a number of these variables. However, the primary focus of this work is on investigating problems entraining and stabilizing air in concrete utilizing fly ash. These investigations include: evaluation of existing and newly created test methods to measure the impact of fly ash on the ability to air-entrain concrete, and the fresh and hardened properties of air-entrained fly ash concrete is investigated. Additional work is presented concerning some of the fundamental physical and chemical properties of air-void shells separated from cement paste and how they change with time.