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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.

The intense vibration of a roadheader rotary table damages the cutting system of the roadheader and reduces the efficiency. This paper analyzes the vibration of a rotary table by combining the finite element model with tested data from an underground coalmine. First, the force of the rotary table during the cutting procedure was analyzed, and the finite element model was built using Pro/E and ADAMS. The tested data were then imported into the model after selection, procession, and combination were conducted. Next, the six lowest-order parameters of the rotary table were calculated. A vibration analysis of the rotary table under certain working conditions was conducted, and the results were compared with those from a modal experiment using a single-point excitation method. According to the comparison between the simulation result and experiments, it is clear that this method is both reasonable and feasible. And it could supplement the theoretical foundation of the analysis of other roadheader components, providing reference for the improvement of the structure and dynamic properties of a roadheader. In addition, other vibration components of a roadheader such as the cutting head and the cutting arm could also be analyzed through the proposed method, with very reliable precision.

A thin boundary layer formed on inner‐pipe wall and brought out wall slip phenomenon when dense pastes were transported in pipe as plug flow. The boundary layer is called slip layer as well, which reduced frictional pressure loss, increased the conveying distance and saved energy consequently. In order to find out the relationship between the properties of boundary layer and the pressure loss, the design of the liquid injection equipment was detailed in this paper. The liquid (such as water, oil or polymer solution) is injected from the pump into the pipe downstream at comparatively small flowrates and formed a lubricating annulus adjacent on the pipe inner wall. By taking coal slime as an example, the test studied pressure loss result from the change of pipeline features and the thickness of boundary layer systematically. Results show that the pressure loss reduced exponentially with the increase of the boundary layer thickness, and the greater the diameter, the smaller the pressure loss. When the shear rate of the boundary layer was getting higher, the lubrication layer played more efficiency on the reduction of the shear stress. Furthermore, these results provide preview for our understanding of the fundamental processes of slime pipe flow and how such flows can be better modelled, optimised and controlled. Copyright © 2017 John Wiley & Sons, Ltd.