Bond Between Layers of Cementitious Mortars Developed for 3D Printing (2023-06)¶

Despite the recent technological advances, there are still no huge advances in the worldwide construction processes. With the Industrial Revolution 4.0, new possibilities emerged, being additive manufacturing, also called 3D printing, using cementitious materials, one of the most promising. This building process has numerous advantages, such as: automation of the construction processes with reduction of labour costs; productivity increase at the prefabrication plant; optimization of shapes and possibility to adopting complex geometries; reduction of raw materials and waste; no need for formwork; among others. Taking into account all the above-mentioned benefits, over the last few years, several research studies were dedicated to improving this building technique and significant progresses were made. However, there are still challenges to be considered, as for instance the reduced bond between layers. In fact, the overlapping of successive layers, printed at different instants, can result in weak bond and, in addition, the absence of formwork earlier exposes the material to the environment conditions and thus increases the time-dependent effects, resulting in higher differential shrinkage between layers. Most recent studies indicate that several parameters also contribute to reduce the bond strength between layers. For these reasons, it has been concluded that 3Dprinted elementsmaydevelop an anisotropic behaviour. This study is dedicated to evaluate the longitudinal shear strength between layers, using pre-selected mixtures. Results are discussed and major conclusions are drawn.