As part of the AiF research project ”Safe pumping of concrete – pumpability and pump stability“ (AiF No. 20947 BG), pumping tests were carried out for the first time with the aim of scientifically investigating the blocking behaviour of concrete during pumping. A practical test set-up was developed that allowed the concrete to be observed during blocking in a time- and location-resolved manner. By deliberately varying various influencing variables such as concrete composition, delivery line routing and the arrangement of various delivery line elements, it was possible to gain a deeper understanding of the interaction between concrete and delivery line. The results will be made available to practitioners in the form of recommendations for action and application and should help to reduce the frequency of blockages in the delivery line, make concrete delivery safer and facilitate the handling of modern concrete mixes.