Influence of Mixture-Composition and Carbonation-Curing on Properties of Sustainable 3D Printable Mortars (2025-01)¶

With increasing coastal populations and loss of marine habitat, artificial structures are increasingly utilized to enhance marine biodiversity. However, conventional Portland cement (PC)-based concrete poses ecological concerns due to its elevated pH, hindering marine life colonization. Previous studies have focused on supplementary cementitious materials (SCMs), but the impact of high-volume SCM replacements on pH reduction and carbonation capacity remains underexplored. This study investigates the use of high-volume SCM replacements (60–75%), particularly silica fume (SF), in 3D-printed concrete for artificial reefs. Results showed that replacing 75% of PC with SCMs effectively reduced the pH from 12.9 to 10.9, while accelerated carbonation further decreased the pH to below 10 after 1-day curing. In these mixtures, a significant improvement in buildability was observed, with an increase of 210–340%, attributed to the enhanced static yield stress from higher SCM content. However, mechanical properties were negatively affected, with compressive strength decreasing by up to 14% and flexural strength by 36% as SCM content increased. These findings offer valuable insights for designing low-pH, eco-friendly concrete materials for marine biodiversity restoration, addressing both material performance and ecological sustainability.