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

Abstract

One-part geopolymers are a low-carbon alternative to Portland cement, and are more suitable in engineering applications compared to two-part geopolymers. In this paper, the effects of mechanical activation on the properties of one-part fly ash/slag-based geopolymer paste and the mechanism of the pozzolanic reaction are studied. Simple mixing was established as the control group, and the effect of mechanical activation on the macroscopic properties of geopolymers was studied through testing compressive strength, fluidity and setting time. The effect of mechanical activation on the pozzolanic reaction of geopolymers was assessed using isothermal calorimetry, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TG-DTG). The results showed that the 28-day compressive strength of geopolymer formed by mechanical activation was 26% higher than that by simple mixing. Workability and fluidity were also enhanced. The reactivity of the precursor was improved by mechanical activation, particularly with fly ash. Mechanically activated fly ash experienced a pozzolanic reaction within 7 days, while undisturbed fly ash produced pozzolanic activity after 14–28 days. The implications of these results in terms of the influence of mechanical activation on pozzolanic activity are subsequently discussed. Highlights · Mechanical activation improved the setting time, fluidity, and compressive strength of one-part fly ash/slag-based geopolymer. · Mechanical activation significantly improved the pozzolanic activity of fly ash. · Mechanical activation lessened the carbonization of one-part fly ash/slag-based geopolymer.