Synchronized concrete and bonding agent deposition system for interlayer bond strength enhancement in 3D concrete printing

A synchronized concrete and bonding agent deposition system is proposed to address the weak interlayer bond strength issue in extrusion-based 3D concrete printing (3DCP). In the proposed system, printable concrete and bonding agent are deposited concurrently via a rotatable nozzle with two outlets. Therefore, the interlayer bond strength is improved by the bonding agent deposited on the interface between printed filaments. Various bonding agents, including water, cement strengthener, polymer solution, and cement paste, were investigated. The results indicate that when the cement paste with a 0.26 water-to-cement mass ratio is adopted as the bonding agent, a relative bond strength as high as 267% can be obtained via the proposed system. Continuous printing was conducted to demonstrate that the proposed system has great potential for practical engineering applications. The proposed system has the potential to eliminate the weakness in interlayer bond strength of 3DCP processes and to widen 3DCP applications.