Development of novel concave and convex trowels for higher interlayer strength of 3D printed cement paste

Past experimental results have shown that the use of nozzle trowels can enhance the interlayer strength of 3D printed cement paste. In this study, the design is further optimized by introducing concave and convex shapes onto the nozzle trowel design. A technique for accurate simulation of the interlayer stresses with the influence of nozzle trowels is established, and it is found that the nozzle trowels double the maximum shear stress and increase the maximum pressure by about 114 %. Moreover, the concave and convex nozzle trowels with removal of interlayer notch further increase the interlayer strength by 35 %. A theoretical model is also proposed to predict the interface geometry and then validated by the experimental observations on the concave and convex trowels. These findings not only result in 3D printed cement paste with much higher interlayer strength, but also emphasize the importance of nozzle designing with optimal interlayer stresses and interface geometries in the application of 3D concrete printing (3DCP).