A thermo-hygro model to determine the factors dictating cold joint formation in 3D printed concrete

Cold joints in extruded concrete structures form once the exposed surface of a deposited filament dries prematurely and gets sequentially covered by a layer of fresh concrete. This creates a material heterogeneity which lowers the structural durability and shortens the designed service life. Many factors concurrently affect cold joint formation, yet a suitable tool for their categorization is missing. Here, we present a computational model that simulates the drying kinetics at the exposed structural surface, accounting for cement hydration and the resulting microstructural development. The model provides a time estimate for cold joint formation as a result. It allows us to assess the drying severity for a given geometry of the structure, its interaction with the environment, and ambient conditions. We evaluate the assessed factors and provide generalized recommendations for cold joint mitigation.