Active Rheology-Control of Concrete Using Encapsulated Accelerator as Responsive Additives for Concrete 3D Printing (2024-09)¶

This paper presents a new technology of on-demand delivery of set accelerators in printable concrete to meet the conflicting rheological requirements in 3D concrete printing (3DCP) . The on-demand delivery is achieved by encapsulating the set accelerators with thermally responsive polymers and mixing the encapsulated accelerators in the initial mixing followed by print head activation using heating to release the accelerators from the capsules. Various encapsulation methods including the gelatine capsules and phase change material (PCM) based capsule and accelerators including shotcrete accelerators, NaOH and Na2SiO3 were investigated. It was found that all encapsulation methods showed excellent pumpability properties before print head activation. On the other hand, the static yield stress (SYS) of printable mixes were significantly enhanced after the print head activation with different set-accelerators resulting in different degree of enhancement. For instance, the SYS at 25 min was increased by 4 times, 4 times and 9 times for the shotcrete accelerator, NaOH and Na2SiO3 respectively. On the contrary, the mechanical properties of the printed concrete were affected differently by the proposed encapsulated accelerator technologies. The corresponding 7-day compressive strength was reduced by 31% and 2% in perpendicular direction for NaOH accelerator and Na2SiO3 accelerator respectively. In contrast, the 7-day strength of the mixture with liquid set accelerator were increased by 26% in perpendicular direction. Finally, a brief discussion on the development of a prototype print head for the proposed method and large-scale print validation was presented.