Working Mechanisms of Air-Entraining Agents

From some job sites it was reported that the air void content of the hardened road concrete was considerably higher than that of the fresh concrete. Initial investigations in the Research Institute with six air-entrainers based on synthetic and natural active agents showed that a substantial increase in air content can occur only if the fresh concrete is supplied with air-entrainer that is inadequately decomposed and activated. The air void content may increase if mixing energy is subsequently applied during placement. A systematic influence of the type of active agent was not detected. As knowledge of the exact interactions of the active agent forming air voids, the mixing time and the quantity added is inadequate, the basic working mechanisms of active agents forming air voids must be determined. With selected active agents the sorption behaviour of the substances generating air voids is investigated using cement paste, while mortar forms the basis for studying air void formation as a function of the type and quantity of the active agent.