Lap Joint Reinforcement for 3D Concrete Printing

Extrusion three-dimensional (3D) concrete printing (3DcP) is an automated construction technology that involves the layer-by-layer deposition of stiff concrete to build a structure without formworks. The interlayer strength is compromised by weak bonds and lack of vertical reinforcements. The bar-penetration technique is a 3DcP reinforcement method where reinforcing bar is inserted vertically through freshly printed layers. Application of a cement paste to the bar during penetration has proven to increase the bar to matrix bond. To be effective as continuous reinforcement, a sequential vertical lapping of bars is considered. For this method to be effective, an understanding of minimum lap length in 3DcP requirements is crucial. This study investigates center- and off-center-lapped samples with lap lengths of 20, 17, 14, and 11 times the bar diameter, subjected to three-point bending tests. Failure modes and crack patterns were recorded and compared with single-bar-penetrated samples. Results and findings were further validated by the printing and testing of a large-scale wall section. Comparisons with small scale results and design calculations showed promising structural performance.