Interlayer adhesion of 3D printed concrete: Influence of layer stacked vertically.

• Using X-CT combined with MIP is a reliable method for investigating the pore feature in printed concrete interlayer interface. • The bond strength in the middle interface of the printed element is higher than that of the upper and bottom interfaces. • The pores in the bottom interface tend to be interconnected or continuous due to the pressure of upper printed layers. 3D printed concrete is an emerging intelligent construction method, and it has been attracting an exponential attention in this sector. However, one of the major issues in printed concrete is the cold joint between the neighbor layers. In this study, an experimental study on the relation between the number of stacked layers vertically and the interlayer adhesion of 3D printed element was conducted. Splitting method was carried out to test the interlayer bond strength, mercury intrusion porosimetry (MIP) and X-ray computed tomography (X-CT) scanner were used to investigate the pore structure of the interlayer zone. The experimental results indicated that a markable influence of the stacked layers vertically on the interlayer adhesion is found. The interlayer bond strength in the middle interface of the printed element is higher than that of the upper and bottom interfaces, especially the bond strength in the bottom interface is the least. Such result is also reflected in the results of the MIP test: the lower total pore volume and total pore surface area existed in the middle interfaces. The X-CT results showed that a large number of elongated and flat pores present in the interlayer zone, the pores in the bottom interface tend to be interconnected or continuous due to the pressure of upper printed layers. An empirical model was proposed to account for the formation of the irregular pore and the change of bond strengths between the vertical neighbored layers of 3D printed element. [ABSTRACT FROM AUTHOR]