Effects and Mechanisms of Modified Superabsorbent Polymers on Shrinkage Behavior of 3D-Printable Mortar (2026-04)¶

Three-dimensional printed mortar (3DPM) is prone to shrinkage and cracking, whereas conventional superabsorbent polymers (SAPs) often reduce mechanical strength. This study investigates nanosilica (NS)-modified SAPs incorporated at 0.3% by mass to enhance the performance of 3DPM. NS-modified SAPs enhanced workability retention, limiting the 2 h slump loss to below 10%, and significantly reduced plastic, autogenous, and drying shrinkage. The C3a mixture, incorporating NS with a particle size of 7 nm at 20% of the SAP mass, exhibited the best performance, achieving a 38.41% reduction in plastic cracking area. The NS-modified SAPs released water to offset early moisture loss and maintained internal humidity at later ages. The organic-inorganic composite membrane refined the pore structure and promoted secondary hydration, forming C-S-H gels that filled voids and strengthened interfaces. The 28 d compressive strength reached 93% of the control, approximately 20% higher than that of unmodified SAPs. Overall, this approach provided an effective balance between shrinkage mitigation and strength retention, thereby improving the durability of 3DPM.