High temperature exposure of alkali-activated coal fly ashes

• Published in: Journal of Building Engineering 2022-11, Vol.59, p.105081, Article 105081
• Main Authors: Seyedian Choubi, Sepehr, Meral Akgul, Cagla
• Format: Article
• Language: English
• Subjects: Alkali-activated fly ash; Mechanical performance; Microstructure; Thermal conductivity; Thermal exposure
• ISSN: 2352-7102; 2352-7102
• DOI: 10.1016/j.jobe.2022.105081

This study systematically investigates the impact of heat exposure on the performance of a wide range of alkali-activated coal fly ashes (AAF). Three low-Ca and three high-Ca coal fly ashes (CFAs) were activated with 10 M NaOH at an activator-to-CFA ratio of 0.5. Prepared pastes were cast into 5 × 5 × 5 cm cubes (for mechanical tests) and Φ6 × 4 cm cylinders (for thermal constant tests), cured at 80 °C for 24 h, and then stored in the fog room for 28 days. Samples were then exposed to 400, 700, and 1000 °C for 1 h and cooled in the furnace. The morphological and mineralogical changes due to heat exposure were studied through X-ray diffraction (XRD), thermogravimetric analysis (TGA/DTA), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR). The performances of the AAF samples before and after heat exposure were evaluated by measuring thermal conductivity (λ), volumetric specific capacity (cvol) and compressive strength. Mechanical performance varied considerably after exposure to elevated temperatures depending on the exposure temperature and intrinsic properties of the activated CFA, low-Ca AAFs being more stable than high-Ca AAFs, whereas exposure significantly reduced λ and cvol values for all AAFs. •Wide range of CFAs were alkali-activated and exposed to high temperatures.•Detailed mineralogical and morphological characterization after thermal exposure.•Mechanical performance varied depending on exposure temperature and intrinsic properties of activated CFA.•Exposure to elevated temperatures significantly reduced λ and cvol.