Effect of mechanical activation on reaction mechanism of one-part preparation fly ash/slag-based geopolymer

Abstract

One-part geopolymers are a greener alternative to Portland cement and are more suitable in engineering applications compared with two-part geopolymers. The effects of mechanical activation on the properties and the mechanism of the pozzolanic reaction of fly ash (FA)/slag-based geopolymer paste prepared using the one-part method were studied. Simple mixing was used for the control group and the effect of mechanical activation on the macroscopic properties of geopolymers was studied using tests for compressive strength, fluidity and setting times. The effect of mechanical activation on the pozzolanic reaction of geopolymers was assessed using isothermal calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. The results showed that the 28-day compressive strength of the geopolymer formed by mechanical activation was 26% higher than that of the geopolymer prepared using simple mixing. Workability and fluidity were also enhanced. The reactivity of the precursor was improved by mechanical activation, particularly for the FA. The mechanically activated FA experienced a pozzolanic reaction within 7 days, while the undisturbed FA produced pozzolanic activity after 14–28 days. In addition, mechanical activation lessened the carbonisation of the one-part FA/slag-based geopolymer The implications of these results in terms of the influence of mechanical activation on pozzolanic activity are discussed.