New insights into the early-age reaction kinetics of metakaolin geopolymer by 1H low-field NMR and isothermal calorimetry

Abstract

Early-age reaction kinetics of geopolymers is one of the challenging issues associated to their mechanical performances and durability. In this work, the early-age reaction of metakaolin geopolymer prepared by activators with various silicate moduli was studied. Compared to conventional methods, a novel approach was firstly proposed to evaluate the early-age reaction of geopolymer by using 1H low-field nuclear magnetic resonance (NMR) and isothermal calorimetry. The state and relative quantity of water in geopolymer pastes were detected by NMR during reaction process. While in this timescale, the heat release of pastes was recorded by isothermal calorimetry. A good consistency to the measurement of reaction process between these two testing methods can be observed. Activator with low silicate modulus (i.e., high alkalinity) deepens the reaction degree at the same timescale and the gel pore volume is increased with the alkalinity of activator. This method is useful to monitor the early-age reaction process of geopolymer, which is expected to offer new insights into the early-age reaction kinetics of geopolymer.