Enhanced shape stability of flowable mortar through CO2 injection for 3D concrete printing application

This study explores the direct injection of CO2 into the 3D printer head during the printing process, enabling real-time control of yield stress evolution in flowable mixtures. CO2 concentrations ranging from 0.5% to 1.4% by cement weight were tested by varying injection times. CO2 injection reduced slump flow of mortar from 250 to 100 mm, as reflected in the decreased width and increased height of printed layers. Mortar with 0.5% CO2 maintained flowability but experienced shape collapse during layer stacking, while higher CO2 concentrations led to nozzle blockages.