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Investigation of Mode I/III Fracture Toughness of Alkali-activated Concrete at Elevated Temperatures

Mahmoudi, Mohammad Reza | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58507 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ghaemian, Mohsen; Toufigh, Vahab
  7. Abstract:
  8. This study investigates the post-fire fracture behavior of alkali-activated slag-based geopolymer concrete (GPC) under Mode I, Mode III, and mixed-mode I/III loading using edge-notched disc bend (ENDB) test with varying water-to-binder ratios. Fracture performance was assessed before and after exposure to elevated temperatures ranging from 25 °C to 800 °C. The degradation of fracture toughness was evaluated by visual inspection, mass loss quantification, and ultrasonic pulse velocity (UPV) measurements. Results revealed that fracture toughness remained relatively stable up to 250 °C due to enhanced slag-activator reaction kinetics, followed by a marked decline at higher temperatures—particularly beyond 600 °C—linked to microstructural degradation. Notably, Mode III (tearing) fractures exhibited superior thermal resistance compared to Mode I (tensile), attributed to the compressive-tolerant behavior of inclined microcracks under shear loading. Among the tested mixes, specimens with low water-to-binder ratios demonstrated the greatest fracture resistance, likely due to their denser matrices and improved thermal stability. A Random Forest (RF) model, trained on nondestructive parameters, achieved excellent predictive accuracy (R² = 0.9639) for fracture toughness. SHAP analysis further highlighted fracture mode and UPV as the most influential features, aligning well with experimental observations
  9. Keywords:
  10. Geopolymer Concrete ; Fracture Mechanics ; Fracture Toughness ; High Temperature ; Mechanical Properties ; Machine Learning ; Post-Fire Damage

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