Understanding the Structural Build-Up-Rate of Cementitious Materials for 3D Printing (2021-09)¶

The concrete 3D-printing technology is highly dependent on the material’s rheology and on the deep understanding of how those properties evolve with time. This evolution occurs due to reversible structural build-up and irreversible chemical phenomena, like hydration reactions. To guarantee structural stability of the printing process, the material, as soon as it is deposited, needs to build-up an internal structure to withstand its weight and the weight of the following layers. Therefore, the static yield stress and how it increases over time at rest becomes of first interest. The concrete structural build-up happens due to both CSH bridge formation by nucleation of cement grains at their pseudo-contact points during the dormant period of hydration, and flocculation due to colloidal interactions. The currently accepted knowledge on the subject relates the yield stress growth with the structural build-up rate of the material through different models, as it also uses different measuring protocols and assumptions to its determination. The goal of this research is to summarize the literature on this topic, identifying the similarities and discrepancies in the available data to further propose a more suitable approach to evaluate this parameter. To do so, a systematic reviewwas carried out in theWeb of Science database with appropriate keywords. Then the data were organized and analyzed taking into account aspects such as the definition of structural build-up, the model used, simplifications/assumptions of the model, experimental protocol, mixture parameter and model limitations.