Quantitative analysis of reaction degrees and factors influencing alkali-activated metakaolin-GGBFS blend

Abstract

The mechanical properties and durability of an alkali-activated metakaolin (MK)- ground granulated blast furnace slag (GGBFS) blend depend on its reaction degree during the alkali activation process. In the present study, the dissolution ratios of MK and GGBFS and their reaction products in hydrochloric acid with different pH values were investigated. The hydrochloric-acid-insoluble matter of MK and its geopolymers were analysed using an X-ray fluorescence spectrometer, X-ray diffractometry, and Fourier transform infrared spectroscopy. It was found that the MK was mostly insoluble and that the MK-based geopolymer was dissolved completely in the hydrochloric acid solution at a pH of 0, and the GGBFS and alkali-activated GGBFS were completely dissolved in the hydrochloric acid solution at a pH of 0–2. Based on the solubility of the raw materials and the alkali activated products, a quantitative analysis approach for the geopolymerisation degree of MK and an MK-slag blend was developed, and the degrees of reaction of the MK and MK-slag blend under alkali activation conditions were studied. It was found that the degree of geopolymerisation reaction of pure MK increases with the increase in the liquid–solid ratio and decreases with the increase in the activator modulus (molar ratio of SiO2 to Na2O) with an activator concentration of 35%. The addition of GGBFS enhanced the degree of reaction of the MK in the MK-GGBFS blend in most cases, particularly under conditions of a low liquid–solid ratio, a high activator modulus, and a low activator concentration. The degree of reaction of the MK in the blend usually first increases and then decreases with the increase in the GGBFS content, and the 40% and 60% GGBFS contents often correspond to the highest degree of geopolymerisation reaction of the MK. However, the degree of the reaction of the MK will continue increasing with the increase in the GGBFS content when activated by an activator with a low concentration.