Yuan et al. (2024) — Feasibility Study of Engineered Geopolymer Composites Based High-Calcium Fly Ash and Micromechanics Analysis

Citation

Yuan, Z., Pang, Z., Lu, C., & Yao, Y. (2024). Feasibility study of engineered geopolymer composites based high-calcium fly ash and micromechanics analysis. Case Studies in Construction Materials, 20, e02701.

• DOI: 10.1016/j.cscm.2023.e02701
• Atlas layer: core
• Related Victor Li book chapter: Chapter 4: Pseudo Strain-Hardening Criteria & Chapter 7: Alternative Reinforcing Fibers (PE Fibers) & Chapter 9: Green ECC (High-Calcium Fly Ash Binders, pp. 307–342)
• Source PDF: yuan-2024-feasibility-study-of-engineered-geopolymer-composites.pdf
• Extracted text: full_text/yuan-2024-feasibility-study-of-engineered-geopolymer-composites_full_text.md
• Source note: source_notes/yuan-2024-feasibility-study-of-engineered-geopolymer-composites_source_note.md

Why this paper matters

A comprehensive experimental and micromechanical study from Southeast University demonstrating that High-Calcium Fly Ash (HFA, 11.2 % CaO) resolves the prolonged ambient setting and low early strength of low-calcium geopolymers, achieving 41.8 MPa compressive strength and 6.20 % direct tensile ductility at room temperature without steam curing.

Main contribution

• Overcomes the engineering bottleneck of slow ambient setting in low-calcium fly ash (LFA) geopolymers by formulating High-Calcium Fly Ash EGC (HFA-EGC: 80 % HFA + 20 % GGBS).
• Investigates the influence of activator sodium silicate-to-sodium hydroxide (SS/SH) ratio (2:1 vs. 1:1) on reaction kinetics, gel structure, and micromechanical parameters.
• Discloses the hybrid hydration mechanism: reactive $\text{Ca}^{2+}$ in HFA accelerates aluminosilicate dissolution, forming co-existing C-(N)-A-S-H and N-A-S-H gels that allow demolding within 24 hours at 20 °C.
• Measures single-fiber pullout and SENB fracture toughness, proving that the 1:1 SS/SH activator (H-Na1) limits matrix toughness ($J_{tip} = 8.6\text{ J/m}^2$) while maximizing complementary bridging energy ($J_b' = 34.2\text{ J/m}^2$), achieving a PSH index of $J_b'/J_{tip} = 3.98$.
• Demonstrates that HFA-EGC achieves a compressive strength of 41.8 MPa (+58 % vs. LFA-EGC), ultimate tensile strength of 5.8 MPa, and direct tensile strain capacity of 6.20 %.

Evidence summary

• Material Matrix Formulations:
• Precursors: High-calcium fly ash (HFA: $44.0\%\ \text{SiO}_2, 28.6\%\ \text{Al}_2\text{O}_3, 11.2\%\ \text{CaO}$) vs. Low-calcium fly ash (LFA: $54.0\%\ \text{SiO}_2, 31.2\%\ \text{Al}_2\text{O}_3, 4.0\%\ \text{CaO}$), blended with 20 % GGBS.
• Activator: $8\text{ M NaOH} + \text{Na}_2\text{SiO}_3$ ($M_s = 3.3$); SS/SH ratios of 2:1 (Na2) and 1:1 (Na1).
• Aggregate: Ultrafine silica sand ($125\text{--}180\ \mu\text{m}, \text{sand/binder} = 0.20$), cured at $20\ ^\circ\text{C}$ ambient room temperature.
• Fiber Specifications: UHMWPE fibers ($V_f = 2.0\text{ vol. \%}, l_f = 12\text{ mm}, d_f = 24\ \mu\text{m}, \sigma_f = 3000\text{ MPa}, E_f = 100\text{ GPa}$).
• Mechanical Results across Systems (28 Days):
• LFA-Na1 (Low-Ca FA, SS/SH = 1:1): $f_c = 26.5\text{ MPa}$, $\sigma_u = 3.8\text{ MPa}$, $\epsilon_u = 4.10\%$.
• HFA-Na2 (High-Ca FA, SS/SH = 2:1): $f_c = 48.6\text{ MPa}$, $\sigma_u = 6.4\text{ MPa}$, $\epsilon_u = 3.80\%$ (higher matrix stiffness).
• HFA-Na1 (High-Ca FA, SS/SH = 1:1): $f_c = \mathbf{41.8\text{ MPa}}$, $\sigma_u = \mathbf{5.8\text{ MPa}}$, $\epsilon_u = \mathbf{6.20\%}$ (optimal strain-hardening).
• Micromechanical PSH Metrics:
• HFA-Na1: Matrix toughness $K_m = 0.32\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 8.6\text{ J/m}^2$, $J_b' = 34.2\text{ J/m}^2$, PSH Energy Index $J_b'/J_{tip} = \mathbf{3.98} \ge 3.0$.

Linked Atlas nodes

• 02_concepts/strain_hardening_criteria.md
• 05_experiments/single_fiber_pullout.md
• 02_concepts/flaw_design.md
• 04_material_systems/geopolymer_ecc.md
• 04_material_systems/green_ecc.md
• 04_material_systems/pe_ecc.md
• 05_experiments/direct_tensile_test.md
• 02_concepts/circular_economy_materials.md

Relationship to Victor Li book

• Extends Victor Li (2019) Chapter 4 (PSH Criteria), Chapter 7 (PE Fibers), and Chapter 9 (Green ECC, pp. 307–342).
• Validates the precursor reactivity micromechanics model: demonstrates how calcium content in industrial pozzolans governs dissolution kinetics and $K_m$, proving that activator stoichiometry (SS/SH ratio) must be tuned to keep $J_{tip}$ low and ensure robust multiple cracking in high-calcium systems.

Claim-evidence rows to add

Verification status

• PDF preserved: yes (yuan-2024-feasibility-study-of-engineered-geopolymer-composites.pdf)
• Text extracted: yes (full_text/yuan-2024-feasibility-study-of-engineered-geopolymer-composites_full_text.md)
• DOI verified: yes (10.1016/j.cscm.2023.e02701)
• Metadata verified: yes (Case Stud. Constr. Mater., Vol. 20, e02701, 2024)
• Claim-evidence matrix ready: yes

Cautions

• High SS/SH ratios ($> 2:1$) in high-calcium systems cause excessive matrix densification, raising $K_m$ and lowering tensile strain capacity; SS/SH should be maintained near 1:1.
• High-calcium fly ash sources exhibit varying free CaO contents; chemical batch testing is recommended to ensure consistent setting times.