Mitigating early age cracking in 3D printed concrete using fibres, superabsorbent polymers, shrinkage reducing admixtures, B-CSA cement and curing measures

3D printed concrete is vulnerable to severe early age shrinkage-related cracking due to the absence of formwork and coarse aggregates. To address this, several potential mitigation measures are compared based on their ability to reduce free shrinkage and cracking severity at dosages which do not adversely affect the printability or buildability of a well-developed 3DPC mixture. The results show that a low dosage of short polypropylene microfibres eliminates early age cracking. The external application of a curing agent and multiple applications of misting water are less effective. Calcium sulfoaluminate-belite cement is used to accelerate structuration and proves beneficial in crack mitigation while enhancing buildability. Internal curing, with superabsorbent polymers, is less effective in mitigating plastic cracks but reduces autogenous shrinkage and increases the rate of stiffening. At the dosage used in this study, the shrinkage reducing admixture is relatively ineffective in crack mitigation, with higher dosages adversely affecting the buildability.

Automated summary

3D printed concrete is prone to early age cracking, but several mitigation measures, including the addition of polypropylene fibers, application of curing agents and misting water, and the use of special cement, can reduce the severity of cracking. Among these measures, polypropylene fibers have the best effect.