Die gezielte Einstellung der für den Frost- und Frost-Tausalz-Widerstand relevanten Luftporenkennwerte ist häufig mit Schwierigkeiten verbunden. Die Ursachen können Wechselwirkungen zwischen den Ausgangsstoffen wie auch Randbedingungen bei der Herstellung, dem Transport und dem Einbau sein. Der Einfluss des Betonzusatzstoffs Flugasche ist in einem unfangreichen Versuchsprogramm am Institut für Bauforschung der RWTH Aachen (ibac) ermittelt worden. Basierend auf vorangegangenen Grundlagenforschungen wurden Reihenuntersuchungen an verschiedenen Chargen einer bestimmten Flugasche sowie vergleichende Versuchsreihen an Suspensionen, Mörteln und Betonen mit und ohne Flugasche durchgeführt. Der Beitrag beschreibt die Untersuchungen und deren Ergebnisse. – Freeze-thaw resistance of air-entrained concrete containing fly ash – Selective adjustment of the air void parameters that are relevant to the resistance to freeze-thaw with and without de-icing salt by artificial introduction of micro air voids into the complex “air-entrained concrete” system has until now always been associated with difficulties. The reasons may be interactions between the starting materials as well as the conditions during production, transport and placement. This contribution focuses on the effect on the overall system of using fly ash as a concrete addition. A series of investigations based on previous fundamental research work were carried out on different batches of a certain fly ash and comparative test series were carried out on suspensions, mortars and concretes with and without fly ash. The fly ash exhibited a uniform air-entraining agent requirement throughout and good system compatibility. The Foam Index proved to be a reliable evaluation criterion. In a site trial based on the laboratory tests the requirements for freeze-thaw resistance tested by the CIF test were fulfilled both by the fly ash concrete and by the reference concrete without fly ash. The investigative scheme described shows how problem analysis and quality assurance during the production of air-entrained concrete can be improved. The importance of site trials also becomes clear because specific influencing factors, such as different weather conditions and the transport, pumping and compaction processes, cannot be simulated realistically in the laboratory. More extensive basic investigations with direct practical relevance are currently being carried out in a research project sponsored by the AiF (Federation of Industrial Research Associations) on the topic of “Air-entrained concretes with plasticizing concrete admixtures” at ibac (the Institute for Building Research at Aachen University of Technology) and at the FIZ (Research Institute of the Cement Industry) with participation by the industry. This can be expected to provide more extensive knowledge about the interaction of the concrete raw materials in air-entrained concrete and possible solutions for dependable production under specific conditions with a constantly increasing diversity of concrete raw materials.