Adhesion evaluation and interface characterization of 3D printed concrete for automatic repair

3D concrete printing can be used for automatic repair, aiming at increasing efficiency and reducing the use of
manpower, as compared to conventional manual repair. Ensuring strong adhesion of the 3D printed materials
and characterizing the interface is crucial for the success of this approach. To this end, we first evaluated the
adhesion performance of 3D printed concrete based on a low-carbon binder, i.e., calcium sulfoaluminate (CSA)
cement. CSA cement pastes with different re-dispersible polymer powder substitution rates were used as coating
before 3D printing. We used two approaches, X-ray computed tomography (CT) and scanning electron micro-
scopy (SEM), to characterize the interface region. Results indicate that the yield stress of the 3D printing material
and the coating material plays an important role in the adhesion in both the fresh and hardened state. Moreover,
the limited adhesion at the overlay interface can be due to the limited contact at the centimeter and micro scale,
as reflected by CT and SEM, respectively. Applying a coating can fill the air voids at the interface, while the
placement of a coating may not improve the bond strength and can even have a negative impact due to the
limited liquid medium at the interface.