Wet joint performance of 3D printed concrete beam segments under flexural loading

Abstract

A segmented 3D-printed concrete (3DPC) beam is designed whose structural reliability depends on a rebar that can withstand tensile stress at the joints between segments under bending moments. In this study, a new approach is for the first time presented on rebar placement after concrete hardening. It details an innovative testing procedure of joint behavior and bonding strength through the use of 3DCP beam segments assembled to form T-shaped beams with an underside groove into which a rebar is inserted. The bonding strength of the rebar embedded in mortar within the semi-circular groove and the wet joints between segments are characterized and validated. Different variables are considered in the modularization of the 3DPC beam segments and bonding stresses between rebar and concrete are studied. To do so, the beam test procedure was adapted to 3DPC beam segments with 3 rebar diameters and 2 segment lengths subjected to 3-point and 4-point bending flexural tests. As a main finding, the results of this research indicated that both rebar and matrix, when properly designed, underwent bonding failure at loads above their theoretical ultimate limit design values, at the yield point of the rebar steel, demonstrating that placement of rebars after hardening of the 3DPC segments can therefore form a structurally reliable joint.