Geopolymer based shaping of fine natural stone and sea sand

The use of fine natural stone sands, which were previously considered waste products of natural stone processing or at best used as aggregates, is becoming increasingly important for the development of valuable products in the construction industry (façade panels for façade greening, bricks) and climate and environmental protection (reef structures, cultivation panels for mussels, fish hotels, revitalization of damaged ecosystems in harbors). In this way, mineral raw material resources are conserved, and the CO2 footprint of the construction industry can be reduced, especially by using cement-free binding agents like geopolymers.
For marine applications, this approach helps to comply with the strict regulatory requirements against the introduction of foreign substances and make an additional contribution to biodiversity. Shapes and structures are specially designed for desired installation sites, but also for locally occurring species that are particularly worthy of protection and adapted for the production to develop species-specific and printable structures.
The extrusion process, which is known for the fabrication of bricks or honeycomb filter ceramic, was qualified for producing building materials based on geopolymers and natural stone sands. To bind the natural stone particles a climate friendly metakaolin-based geopolymer was used. It was selected due to its very good strength properties and the natural plasticity of metakaolin. Hardened extrudates were mechanically tested with resulting flexural strengths of 7.8 MPa and compressive strengths of 53.5 MPa. These values are in the range of a normal concrete of medium to high strength and make the material a promising candidate for use in the construction industry.