Mix Design Optimization of 3D-Printed Cementitious Composites for Marine Applications (2025-06)¶

The rise in coastal development and the growing efforts to rehabilitate marine environments have increased the demand for underwater sustainable and durable construction materials. Concurrently, 3D concrete printing has gained attention as a promising technology for building artificial reefs, providing benefits in terms of design flexibility and customization compared to traditional construction methods. Despite previous efforts to develop low-pH, biocompatible 3D-printed mortars, the durability of these materials under aggressive marine conditions remains underexplored. This study addresses this gap by development and testing of fiber-reinforced, low-pH, 3D-printed mortars incorporating high-volume supplementary cementitious materials (SCMs), polyvinyl alcohol (PVA) fibers with the effect of early accelerated carbonation (AC) curing. The integration of extrusion-based 3D printing and optimized mix design improved matrix densification and fiber distribution, resulting in higher compressive and flexural strengths compared to cast specimens. Fiber addition, especially at 0.50 vol%, enhanced toughness, ductility, and freeze-thaw resistance by reducing mass loss and mitigating microstructural damage. Underwater abrasion resistance of 3D-printed specimens improved by up to 38 % with fibers, highlighting their role in resisting surface erosion. The presence of SCMs was found to significantly enhance the chloride resistance, while reducing penetration depth by up to 83 %, though AC curing resulted slight increase in porosity. Overall, the results underscore the performance of optimized 3D-printed mortars with improved mechanical and durability properties under harsh marine conditions, and open up new possibilities in sustainable 3D printing of artificial reef structures, and marine infrastructure.