Long-Term Durability and Degradation Mechanisms of 3D Printed Geopolymers (3DPG) With/Without Healing Agents in Marine Environments (2025-12)¶

The degradation performance and mechanisms of 3D printed geopolymers (3DPG) under atmospheric (atmospheric zone, AZ), seawater submerged (submerged zone, SZ), intertidal (tidal zone, TZ) conditions over 12 months exposure were evaluated by monitoring their large-scale properties (apparent morphology, mass change, mechanical behavior), combined with microstructural analysis of pore structure and reaction product distribution, aggressive ions' penetration depth and distribution. AZ samples showed minimal mass change and steadily increasing strength over time. SZ samples' mass increased due to salt absorption, but surface aggregate precipitates; the mechanical strength first increased and then decreased. TZ samples' mass continuously losses, the mechanical strength first increased and then decreased. Notably, adding healing agent significantly enhanced the mechanical properties of 3DPG. 3DPG exhibited vertical layering pore distribution characteristics and had no high interlayer porosity defects after seawater erosion. With increasing erosion time, porosity increased in AZ samples; both SZ and TZ samples experienced decreasing porosity and reduced pore throat number and length. After seawater erosion, AZ samples formed geopolymer gel, Ca(OH)2, CaCO3, with minimal Cl− or SO42− penetration. SZ samples have geopolymer gel with deeper Cl− penetration (6.0 mm) and SO42− intrusion (2.0 mm). TZ samples contained gel and CaSO4, showing the deepest Cl− infiltration (>10.0 mm) and an SO42− enrichment peak at 2.0 mm depth. Prolonged erosion progressively leached Ca2+ from SZ and TZ samples, causing geopolymer decalcification, increasing the Na/Ca ratio, disrupting the gel's change balance and structural integrity, distorting the 3D network, reducing stability, with salt recrystallization caused by tidal action exacerbating damage.