Early age shrinkage mitigation and quantitative study on water loss kinetics of 3D printed foam concrete modified with superabsorbent polymers

Due to direct exposure to the environment during the printing process and after printing and its own porous characteristics, 3D printed foam concrete (3DPFC) will inevitably have a large shrinkage at early age. In this study, the early age shrinkage of 3DPFC was modified by using various dosages of superabsorbent polymer (SAP). The water loss kinetics of 3DPFC at early age were elucidated, and the mechanism influencing early age shrinkage of 3DPFC was revealed. The 8-hour total shrinkage of 3DPFC with two foam contents was reduced by 23.1% and 24.3% at most, respectively. Based on low-field nuclear magnetic transverse relaxation time, liquids in bubble liquid film, capillary pores of the matrix, and inside SAP were quantified and tracked in real time. Under exposure conditions, there exists a quantitative relationship between internal water loss variations in 3DPFC and the matrix T₂₁ peak water (water adsorbed by binder particles and small capillary water between particles), bubble volume fraction, and surface tension of the matrix pore solution. The early age shrinkage of 3DPFC is indeed influenced by the combined effect of water loss and bubble volume fraction.