Concrete Pumping and its Effect on the Air Void System

Pumping is the most utilized concrete placement technique on construction sites around the globe. Despite being used since the 1960s, a large portion of the knowledge related to the understanding of the concrete pumping process-especially with a focus on the effect of pumping on the concrete air void system-was generated through experience, and thus creating a need for a research-based approach to broaden our understanding of the process and how it affects in-place concrete properties. In this paper, three research campaigns are described. Two controlled large-scale experiments investigating both conventional concrete (CVC) and self-consolidating concrete (SCC) were conducted, in addition to a field research program where concrete pumping in real-world conditions was studied. The air void system of each pumped concrete mixture was characterized before and after pumping, both in plastic and hardened states. Additionally, concrete pressure during pumping was monitored for CVC mixtures. Lastly, Super Air Meter measurements were conducted on fresh concrete. It was shown that the characteristics of the pumping system, such as boom configuration, flow rate, or pumping pressure, do not correlate with the changes in the air void system due to pumping for CVC, however, a relationship between the change in the spacing factor and concrete flow rate was observed for SCC. Our results also indicate that the changes in the air void system induced by pumping are dependent on the particular mixture design and discharge conditions at the point of placement