Study on the influence mechanism of micro-mechanical properties of heterogeneous geopolymer gels

Geopolymers are inorganic, environmentally friendly cementing materials, and they exhibit broad application prospects in geotechnical engineering. These are formed by alkali activation and solidification with silicon- and aluminum-rich minerals or wastes as raw materials. Previous studies have revealed that the physical and mechanical properties of geopolymers from various raw materials differ significantly, which is closely aligned with those of geopolymer gels produced by alkali-activated hydration. However, no current systematic theory can explain these differences, so the design of mix proportions of raw materials and activators is particularly blind when preparing geopolymers. To solve this problem, this paper studies the composition and mechanical properties of the slag geopolymer by nano-indentation tests. On this basis, Raman mapping and SEM-EDS tests revealed the information of the polymerization degree and elemental composition of calcium silicoaluminate hydrate (CASH) in the heterogeneous gel phase. Finally, we carried out a verification test combined with ion implantation technology. The results revealed that the direct source of the difference in the mechanical properties of gel phases was the polymerization degree of CASH, and a secondary reason was the atomic ratio of active silicon to aluminum in CASH. Furthermore, the micro-mechanical properties of the gels could be improved by appropriately increasing the concentration of Al element. The results demonstrated the influence mechanism of mechanical properties of heterogeneous gel phases on the molecular scale, which helped evaluate the potential of raw materials to form specific gel phases and thus guided the scientific preparation of high-performance geopolymer materials.