3D-printing concrete technology has attracted more and more attention for smart construction due to its advantages of digitization, automation, and high degree of intelligence. This article introduces the basic principles and related processes of concrete 3D-printing technology, and reviews the development from the following four fields: the material properties, preparation technology, printing parameters, and evaluation criteria of 3D-printing concrete technology. Then the existing difficulties, development direction and key technologies of 3D-printing concrete are described. Finally, we look forward to the development prospects of 3D-printing concrete from the aspects of printing materials, software and hardware cooperation, printing technology, etc. All the researches will provide the useful references for the later development and research.

In high-pressure pulsatile pipeline transport of high-concentration viscous paste, severe backflow is generated when there are sudden pressure drops due to the paste's elastic recovery, resulting in strong impact and damage to the pipeline system. The paste demonstrates high viscosity, yield stress, compressibility, and shear elasticity. Nevertheless, the effect of the paste's elastoviscoplasticity properties on unsteady flow during pipeline transport remains uncertain. Consequently, we derived the unsteady flow control equations of the paste that accounts for the elastoviscoplasticity behavior and linear compressibility. We conducted experimental research by building a circulating pipeline transportation system and performed numerical analysis using the finite-volume method (modified RheoFoam solver). The results demonstrate a substantial increase in pressure fluctuations within the pipeline during rapid pressure drops due to the elasticity of the paste. When accounting for elasticity, the maximum backflow velocity increases by 32.4% compared to cases where elasticity is not considered. The backflow velocity during piston pump reversal is influenced by the pressure level and the rate of pressure drop. Pressure fluctuations are more likely to propagate along the pipeline during high-pressure than during low-pressure periods. These findings offer guidance for analyzing unsteady flow characteristics in paste pipeline transport and designing pipeline systems.