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Geopolymers and alkali-activated materials have emerged as a complement, and partly as an alternative, to traditional materials in various applications, such as traditional ceramics, energy saving, waste management, building construction, and filtration. These new materials can play an important role in mitigating climate change and promoting a circular economy, which is one of the reasons why they are being actively researched in many laboratories around the world.
Open Ceramics, the official, peer-reviewed, Open Access journal of the European Ceramic Society, is dedicated to foster this research and is compiling a Special Issue with the title “Alkali-activated and geopolymer materials in ceramics and various applications”. The aim of this Special Issue is to promote new applications, the use of previously underused raw materials, and in particular a better understanding of the chemical and mechanical behavior of these materials.
The scope of the Special Issue includes, but is not limited to, research on the following topics:
- valorization of previously underused raw materials
- a better understanding of established raw materials
- detailed spectroscopic characterization of alkali-activated materials and geopolymers to elucidate their phase assemblage
- the mechanism of formation of the phase(s) that comprise these binders
- control of their mechanical properties
- the effect of fillers/aggregates on their mechanical properties
- their durability under various conditions and the underlying deterioration mechanisms
- special applications and recycling-related considerations.
Additive manufacturing (3D printing) of ceramics and other materials offers significant advantages compared to conventional production processes for several applications. While ceramics have been extensively investigated in this regard, additive manufacturing of geopolymers have received much less attention to date. In the present contribution we study a ‘standard’ metakaolin-based geopolymer, a fly ash-based geopolymer and a silica-based one-part geopolymer regarding their suitability for additive manufacturing via selective laser curing. Model geometries such as bars and cuboids could be produced by this route. After selective laser curing the specimens were additionally cured at 80 °C for 24 h. The specimens were studied by means of scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). SEM showed that the precursors in all geopolymers had reacted partially and geopolymeric gel had formed. XRD confirmed these results and additionally revealed that the crystalline byproducts (zeolites) in the one-part geopolymer differed from the byproducts observed in conventionally produced samples. This indicates that also the geopolymerization reactions differ between the two synthesis routes. The mechanical strength after selective laser curing and 80 °C-curing appeared to be highest for the metakaolin-based geopolymer. However, SEM also showed that a significant volume of macropores remained in most regions of all specimens, while some regions in the metakaolin-based geopolymer appeared to be significantly denser. These preliminary results demonstrate that selective laser curing offers potential for the production of geopolymers, but more research has to be undertaken to optimize the process.