Effect of pumping process on the properties of 3D printed concrete containing air-entraining agent

Using 3D printing technology in the construction industry is growing rapidly due to its numerous advantages. However, understanding various influencing factors on this technique is crucial. Among these, the concrete pumping process can significantly impact printed concrete's properties. The results indicate that the pumping process can alter the structure of void spaces, reduce the air content, and increase the compressive strength of concrete. Mainly, the mechanisms of mechanical entrapment, reduction of air content and increase of hydration kinetics respectively cause these changes in air content and compressive strength due to pumping. In the control samples, the fresh air content decreased by 47% and the compressive strength increased by 4.3%. The creation of stable air bubbles using air-entraining agents can lead to a decrease in change of air content and compressive strength. By using 0.12% air-entraining agent, the drop in air content due to pumping reached about 23–25%. It also appears that, depending on the amount of entrained air in the mixture, pumping can affect its flowability differently.