Preparation of coal gasification coarse slag-based alkaline activator and its activation mechanism in alkali-activated slag

Abstract

The good performance and durability of alkali-activated slag (AAS) make it to be a potential alternative to ordinary Portland cement. However, the preparation of activators such as water-glass is energy-intensive. In this paper, the feasibility of using a novel activator derived from coal gasification coarse slag (CGCS) for the preparation of AAS was investigated. The CGCS-based activators were the filtrates of CGCS and NaOH compound solution at 150 °C with different CGCS/NaOH ratios. By comparison with water glass-activated slag and NaOH-activated slag, the hydration reaction activity, mechanical property, hydrates composition, and microstructure of the CGCS-activated slag were studied. The results indicate that the compressive strength of CGCS-activated slag reached to 55.25 MPa at 28 d, much higher than NaOH-activated slag (43.08 MPa). CGCS-activated slag also performed the similar hydration dynamic to water glass-activated slag in terms of early heat release and hydrates assemblage. The amorphous silicon from CGCS dissolved in the filtrate played a crucial role in the activation effect of CGCS-based activator, which promoted the early hydration of CGCS-activated slag and contributed to the C-(A)-S-H with longer chain length. These findings proposed the mechanism of slag activated by CGCS-based activator, and provided an eco-friendly strategy for AAS production.