Optimizing calcination temperature to improve the compressive strength of coal gasification slag-based alkali-activated materials by reducing carbon content and adjusting polymerization degree

Abstract

The efficient utilization of coal gasification slag (CGS) to prepare alkali-activated materials (AAMs) presents a significant opportunity for addressing the challenges associated with solid waste accumulation and environmental degradation. However, the aluminosilicate glass in CGS is highly polymerized, rendering it challenging to stimulate its potential reactivity. Additionally, the presence of residual carbon impedes the hydration process in AAMs, thereby limiting its applicability. This study focuses on the residual carbon content and polymerization degree of CGS after calcination treatment to overcome these challenges and improve the reactivity of CGS. Results revealed that residual carbon in CGS underwent thermal decomposition, increasing the proportion of aluminosilicate glass components. The degree of polymerization of CGS was reduced by 25 % under calcined conditions at 550°C, whereas at 700°C, CGS recrystallized, and the aluminosilicates were again highly polymerized. The highest reactivity of CGS was observed after calcination at 550°C. The 28 days compressive strength of the prepared AAM paste reached 47.5 MPa, representing an increase of 18.45 % compared to the control. This study innovatively elucidates the physicochemical properties of calcined CGS. It highlights the critical importance of controlling calcination conditions to manage the polymerization degree and phase transformations during carbon removal, thereby enhancing the reactivity and performance of AAMs.