Factors Affecting the Formation of Air Voids in Road Concrete

A greatly increased air void content in the hardened concrete has been found in recent years in some contract sections of concrete pavement. Investigations were carried out at the Research Institute of the Cement Industry on road concretes in order to determine the reason for this excessively high content. The test results show that a substantial increase in air content can only occur if air-entraining agents in the fresh concrete are not adequately broken down during production, due to too short a mixing time, and have therefore been insufficiently activated. The air content can then rise if mixing energy is introduced into the fresh concrete later during production of the pavement. Practical recommendations for future concrete production are given to avoid excessive air void formation during the placement of concrete.