Reaction kinetics and microstructure evolution of tuff-based geopolymers with feature properties

This work proposes a multi-scale composition design strategy to investigate reaction kinetics, microstructure control, and performance optimization of tuff-based geopolymers in both high- and low-calcium systems. We evaluated the leaching of Al and Si from tuff in alkaline solutions, employing in-situ Raman mapping spectroscopy to track phase structure transitions during leaching. The reaction process of tuff-based geopolymers was assessed using ¹H low-field NMR and ICC. Notably, high-calcium systems showed excellent workability (flowability and setting time) and compressive strength, while low-calcium systems exhibited superior flexural strength. Microstructure characterization via SEM-EDS, XRD, MIP, and TGA elucidated the mechanisms underlying physical property changes. In-situ FTIR further revealed reaction mechanisms and stability within the geopolymer matrix. For high calcium system, some gel nucleus part occurs in the solution with the other part using GGBS and tuff as crystallization nucleus to generate C(N)-A-S-H gels on the surface. For low calcium system, three-dimensional amorphous network structures of N-A-S-(H) gels become the main products, and the tuff particles as crystallization nucleus become the main structure aggregate. This composition design strategy offers valuable insights for the diversified design of tuff-based geopolymers.