Does early age creep influence buildability of 3D printed concrete? Insights from numerical simulations

Cementitious materials may exhibit significant creep at very early age. This is potentially important for concrete 3D printing, where the material is progressively loaded even before it sets. However, does creep actually affect the buildability of 3D printed concrete? Herein, the influence of early-age creep on the buildability of 3D printed concrete is studied numerically. Creep is considered using the "local-force method", which was developed in our previous work. This 3D printing model be used to quantify the influence of early-age creep on typical failure modes, i.e., structural instability due to buckling and plastic collapse resulting from material yielding. The green strength and early-age creep experiments are conducted to characterize early-age visco-elastic-plastic behaviors. The model is then validated with the comparison to printing experiment about buildability quantification and failure mode prediction. Parametric analyses are subsequently performed to quantify the influence of early-age creep on various printing geometries in which different failure modes are dominant. The numerical results highlight the significance of initial printing time and material mix design for predicting the buildability of 3D printing of concrete. Finally, a discussion on how creep affects structural buildability is given from the perspective of localized damage and element strain.