Low-carbon Microwave-assisted activation of coal gasification slag as supplementary cementitious materials

This study aims to investigate a new type of low-carbon activation technology: microwave activation, and its potential influence on the volcanic ash activity of coal gasification slag (CGS) when used as a supplementary cementing material.Mechanically ground coal gasification slag (CGS-30) was subjected to microwave activation at varying power levels (500 W, 800 W, and 1000 W). The pozzolanic activity was assessed through activity index testing and the compressive strength of Portland cement (PC) paste containing 30% slag. Simultaneously, microstructural changes were analyzed using a range of advanced characterization techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), inductively coupled plasma optical emission spectrometry (ICP), nuclear magnetic resonance (NMR), backscattered electron (BSE) imaging, and thermogravimetric analysis (TG). The results demonstrate that microwave treatment substantially enhances the reactivity of CGS. An optimal microwave power of 800 W was identified, at which the activity index of CGS-30 reached 94.31% after 28 days, and the compressive strength of the blended cement paste increased by 22.51% compared to untreated samples after 7 days. Microwave activation facilitates the transformation of crystalline SiO₂ into an amorphous phase, reduces the degree of polymerization within the silicon-oxygen network, and enhances the leaching rate of Al³⁺ ions, thereby increasing the availability of surface-active components. This research offers valuable insights into the development and application of microwave-activated CGS as a supplementary cementitious material.