# Geopolymer Materials for Additive Manufacturing: Chemical Stability, Leaching Behaviour, and Radiological Safety

## TL;DR

This paper studies geopolymer materials for 3D printing, focusing on their chemical stability, leaching behavior, and safety in underwater construction.

## Contribution

The study introduces two metakaolin-based geopolymer formulations optimized for underwater additive manufacturing and evaluates their environmental safety.

## Key findings

- Leaching tests showed stable leachates with most ions immobilized and within regulatory thresholds.
- Radioactivity screening confirmed low radionuclide activity, well below regulatory limits.
- Minor leaching issues were identified, indicating areas for mix improvement.

## Abstract

Geopolymers are inorganic aluminosilicate binders formed by alkali activation of reactive powders, offering a sustainable, low-carbon alternative to Portland cement. Their rapid setting and chemical durability make them well-suited for additive manufacturing (AM) in demanding environments, including underwater construction, where chemical stability is essential for both structural integrity and environmental safety. This study evaluates two metakaolin-based formulations designed for underwater extrusion, differing in activator chemistry and rheology control. Standardized leaching tests revealed alkaline but stable leachates with strong immobilization of most ions; major anions and total dissolved solids remained within regulatory thresholds. Limited exceedances were observed—soluble organic carbon in the NaOH-activated mix and arsenic/selenium in the waterglass–sand system—highlighting specific areas for mix improvement rather than fundamental limitations of the material. Complementary radioactivity screening confirmed activity concentration indices well below the regulatory limit, with measured radionuclide activities falling comfortably within exemption ranges. Together, the leaching and radioactivity results demonstrate that both formulations provide robust matrix integrity and environmental compatibility, while highlighting clear opportunities for mix design improvements to further minimize ecological risks.