Study on the nucleation process of reaction products in geopolymer by in situ test using Raman microscopy

Abstract

This study investigates the growth process of reaction products in geopolymer by in situ test using Raman microscopy and the new analysis procedure. Geopolymer is a new cementitious material which solidifies by the dehydration-polycondensation reaction of alumina-silica precursors. It has been proposed as a replacement for ordinary Portland cement as the primary construction material, and as one of the construction materials used in space. In addition, the application of geopolymer has also shown the potential to reduce radio interference caused by concrete structures. However, the reaction mechanism is not yet clear and a method for controlling its performance has not been established. This study focuses on the visualization of growth process of reaction products in order to clarify the nucleation mechanism, which is the main factor influencing the microstructure and mechanical properties of geopolymer. The system was constructed for in situ Raman microscopy while samples were cured at a high temperature to accelerate the reaction, and the same area scans were repeated for fly ash-based geopolymer up to 24 hours after mixing. The Raman spectrum of reaction products was defined as the difference between the average spectrum of the first and last scans, because the Raman spectrum of reaction products of geopolymer has not been clarified due to their amorphous structure. Finally, the obtained Raman mapping images at each time step are the first visualization of the growth of reaction products in geopolymer.