Effects of K+ and CO32− on the performance of slag–ceramic blended geopolymers

Abstract

Binders developed by using activation technology have received considerable attention as alternatives to Portland cement. The aim of this study was to investigate the effect of introducing K+ and CO32− into geopolymer samples on the properties of alkali-activated slag cement (AASC) composed of blast furnace slag (BFS) and ceramic waste powder (CWP). The CWP replaced 20% of the BFS in the AASC. The activator solutions used were Na2SiO3–NaOH (NSNH), Na2SiO3–KOH (NSKH), and K2CO3–NaOH (KCNH) hybrid solutions. Parameters for evaluating the samples included the heat of hydration, thermogravimetric and differential thermogravimeric curves, ultrasonic pulse velocity, compressive strength, attenuated total reflectance–Fourier transform infrared spectra, X-ray diffraction patterns, and resistivity. The results showed that after K+ was introduced into the geopolymer (NSNH to NSKH), the compressive strength of the NSKH sample was increased. Consequently, the formation of a hydrotalcite phase was promoted and that of a calcium aluminosilicate hydrate (CASH) gel was inhibited. After K+ and CO32− were introduced simultaneously (NSNH to KCNH), the compressive strength of the KCNH sample decreased, and the surface resistivity increased significantly. Moreover, the peak of the exothermic hydration rate moved forward. The accumulated hydration heat increased and carbonates were formed, thereby altering the composition of the three-dimensional network structure of the CASH gel, which significantly contributed to its strength.