In-situ X-ray tomographic imaging of microstructure evolution of fly ash and slag particles in alkali-activated fly ash-slag paste

Abstract This paper presents an in-situ investigation of the microstructure evolution of fly ash and slag particles in alkali-activated fly ash-slag paste using X-ray microcomputed tomography. Results indicate that the dissolution of fly ash and slag particles is not uniform especially for the particles with large size due to the heterogeneous distribution of chemical composition and initial defects. The dissolution of the particles with small size is faster than that of large particles owing to the relatively high specific area. The formation of reaction products (i.e., inner products) is mostly accumulated within the boundary of original particles, which become a barrier to prevent the further dissolution of unreacted particles. The fly ash-slag interaction in terms of microstructure evolution is not obvious at early ages (1–3 d) but becomes apparent at later ages (7–28 d), which can be attributed to the continuous transport of dissolved ions between fly ash and slag.