Initial plastic shrinkage of 3D-printed concrete incorporating recycled brick fine aggregates: Insights from water transport and structural evolution

Due to factors such as low water-to-cement ratio, high cement content, absence of formwork, and high surface area-to-volume ratio, 3D-printed concrete (3DPC) is prone to early plastic shrinkage and cracking, posing risks to mechanical properties and long-term durability. This paper investigated the influence of substituting natural river sand with recycled brick fine aggregates (RBFA) on the performance of 3DPC during plastic phase of hydration. In this study, two different strategies for incorporating RBFA were evaluated: dry RBFA-D and water-saturated RBFA-W. The water absorption-release characteristics of RBFA impact water evaporation rate, the growth of capillary pressure and the evolution of elastic modulus, thereby influencing the plastic shrinkage of 3DPC. RBFA-W continuously releases water into the paste, offsetting water evaporation, decreasing the rise in capillary pressure, and thereby reducing plastic shrinkage. Conversely, adding RBFA-D speeds up capillary pressure growth, yet its rapid increase in elastic modulus strengthens its capacity to resist plastic shrinkage. Based on the water transport, structural development, and plastic shrinkage evolution, three clear stages were distinguished in this research. This study presents a new strategy to mitigate plastic shrinkage of 3DPC using RBFA.