Mitigating Early-Age Cracking in 3D Printed Concrete Using Fibers, Superabsorbent Polymers, Shrinkage Reducing Admixtures, B-CSA Cement and Curing Measures (2022-06)¶

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.