Fracture properties and microstructure formation of hardened alkali-activated slag/fly ash pastes

S. Zhang, Z. Li, B. Ghiassi, S. Yin, G. Ye

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This study presents a comprehensive experimental investigation on the fracture properties of hardened alkali-activated slag/fly ash (AASF) pastes in relation to the microstructure formation and reaction product composition. The main reaction product in AASF is C-(N-)A-S-H gel along with minor hydrotalcite phase, with the polymerization of C-(N-)A-S-H gel substantially governed by its Ca/Si ratio. Strong positive correlations are identified between the Ca/Si ratios of C-(N-)A-S-H gel and the fracture properties KIc (Jtip), whereas, the compressive strength of AASF pastes is primarily determined by its capillary porosity (>0.01 μm). The disagreements between the Ca/Si ratios and corresponding intrinsic mechanical properties of C-(N-)A-S-H gel as proof by contradiction indicate that the fracture properties KIc (Jtip) of AASF pastes could be dominated by a cohesion/adhesion-based mechanism. These findings provide promising guidance for fine-tuning the fracture properties of AASF and also advise on the tailoring strategies for high-performance composite such as strain-hardening geopolymer composite.
Original languageEnglish
Article number106447
Number of pages15
JournalCement and Concrete Research
Early online date8 Apr 2021
Publication statusPublished - Jun 2021


  • Fracture toughness
  • Alkali-activation
  • Slag
  • Fly ash
  • Microstructure
  • Ca/Si


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