Micromechanical analysis of alkali-activated fly ash-slag paste subjected to elevated temperatures

To advance the development of high-temperature/fire-resistant alkali-activated materials, it is vital to understand their behaviour subjected to elevated temperatures. This paper presents a systematic experimental study on microstructural characteristics and micromechanical properties of alkali-activated fly ash-slag paste (AAFS) after exposure to 20–800 °C. The microstructural evolution in terms of morphology, phase assemblage and gel compositions was examined using backscattered scanning electron microscope-energy dispersive spectrometry (BSEM-EDS), while atomic force microscopy (AFM) and nanoindentation tests were conducted to evaluate the micromechanical properties at elevated temperatures. Results indicate that the volume fraction of unreacted particles drops from 29.7 % to 4.0 %, whereas porosity in AAFS paste goes up from 4.1 % to 15.4 % at up to 800 °C. The average hardness and elastic modulus are in the ranges of 0.6–14.5 GPa and 27.0–104.2 GPa, respectively. Based on the obtained experimental results, the microstructure-micromechanical property relations and inherent damage mechanisms were then discussed in depth from a multiscale viewpoint.