The Environment’s Effect on the Interlayer Bond Strength of 3D Printed Concrete

Estimating the bond strength between extruded concrete filaments is of paramount importance for the structural design of 3D printed concrete elements. This study investigates the effect of the environmental printing conditions at various pass times on the interlayer bond strength (IBS), elaborates on the underlying mechanism and investigates a possible mitigation measure. Elements are printed with seven different pass times ranging from 1 min to 30 min while exposed to a benign (indoor-like) and severe (site-like) evaporation rates. The IBS is quantified through flexure tests, with the interlayer aligned vertically, at a concrete age of 28 days. The experimental results show that increasing the pass time from 1 min to 30 min decreases the IBS by 107% for the benign condition. When the specimens were exposed to the severe evaporation rate for 30 min the IBS decreased an additional 35%. Applying a curing compound to the exposed filament surface, to reduce the moisture evaporation, weakened the bond strength.