Nguyễn et al. (2023) — Micromechanical and Mineralogy Analyses on Extremely Ductile Engineered Geopolymer Composites with Different Activator Pretreatments

Citation

Nguyễn, H. H., Lương, Q.-H., Nguyễn, P. H., Kim, H.-K., Kim, Y., & Lee, B. Y. (2023). Micromechanical and mineralogy analyses on extremely ductile engineered geopolymer composites with different activator pretreatments. Journal of Building Engineering, 80, 108093.

• DOI: 10.1016/j.jobe.2023.108093
• Atlas layer: core
• Related Victor Li book chapter: Chapter 4: Pseudo Strain-Hardening Criteria (PSH Performance Indices) & Chapter 7: Alternative Reinforcing Fibers (PE Fibers) & Chapter 9: Green ECC (Fly Ash Geopolymers, pp. 307–342)
• Source PDF: nguyen-2023-micromechanical-and-mineralogy-analyses-on.pdf
• Extracted text: full_text/nguyen-2023-micromechanical-and-mineralogy-analyses-on_full_text.md
• Source note: source_notes/nguyen-2023-micromechanical-and-mineralogy-analyses-on_source_note.md

Why this paper matters

A breakthrough study from Chonnam National University discovering that alkaline activator thermal pretreatment controls early geopolymerization kinetics, where pre-cooling the activator to 10 °C lowers matrix fracture toughness ($K_m = 0.35\text{ MPa}\cdot\text{m}^{1/2}$) and boosts direct tensile strain capacity to an extraordinary 18.6 % with low composite density ($\rho < 1.7\text{ g/cm}^3$).

Main contribution

• Develops Extremely Ductile Engineered Geopolymer Composites (ED-EGC) combining Class F fly ash, pretreated hybrid activators (SMP + SH), and 2.0 vol. % PE fibers.
• Discovers that activator thermal pretreatment directly governs matrix fracture toughness and fiber bridging kinetics:
• Cooling Pretreatment (CP at 10 °C) suppresses early silicate polymerization, lowering matrix crack tip toughness ($J_{tip} = 12.1\text{ J/m}^2$) and driving the PSH energy index to $J_b'/J_{tip} = 14.8$.
• Warming Pretreatment (WP at 50 °C) accelerates geopolymeric cross-linking, elevating compressive strength ($f_c = 28.5\text{ MPa}$) with $\epsilon_u = 11.2\%$.
• Establishes an unprecedented direct tensile strain capacity of 18.6 % in the CP-EGC mixture under uniaxial dogbone tension, with saturated multiple microcracking (average crack width $< 150\ \mu\text{m}$).
• Analyzes N-A-S-H gel nanostructure and fiber-matrix interfacial morphology via SEM-EDS and Backscattered Electron (BSE) imaging.

Evidence summary

• Material Matrix: 100 % Class F Fly Ash, sodium metasilicate pentahydrate ($\text{Na}_2\text{SiO}_3\cdot 5\text{H}_2\text{O}$, SMP) + $\text{NaOH}$ (SH), $w/b = 0.33$, density $\rho < 1.70\text{ g/cm}^3$.
• Fiber Specifications: 2.0 vol. % UHMWPE fibers ($l_f = 12\text{ mm}, d_f = 24\ \mu\text{m}, \sigma_f = 3000\text{ MPa}, E_f = 100\text{ GPa}$).
• Micromechanical & Fracture Parameters:
• CP-EGC (Cooling 10 °C): $K_m = 0.35\text{ MPa}\cdot\text{m}^{1/2}$, $E_m = 10.1\text{ GPa}$, $J_{tip} = 12.1\text{ J/m}^2$, $J_b'/J_{tip} = 14.8$, $\sigma_0/\sigma_{fc} = 1.85$.
• WP-EGC (Warming 50 °C): $K_m = 0.44\text{ MPa}\cdot\text{m}^{1/2}$, $E_m = 13.8\text{ GPa}$, $J_{tip} = 14.0\text{ J/m}^2$, $J_b'/J_{tip} = 10.2$, $\sigma_0/\sigma_{fc} = 1.62$.
• Macroscopic Mechanical Properties:
• CP-EGC: Compressive strength $f_c = 21.4\text{ MPa}$, Ultimate tensile strength $\sigma_u = 4.80\text{ MPa}$, Tensile strain capacity $\epsilon_u = \mathbf{18.60\%}$.
• WP-EGC: Compressive strength $f_c = 28.5\text{ MPa}$, Ultimate tensile strength $\sigma_u = 5.60\text{ MPa}$, Tensile strain capacity $\epsilon_u = \mathbf{11.20\%}$.
• Mineralogy: SEM-EDS confirms that pure 3D N-A-S-H gel forms the continuous binding skeleton, providing stable frictional pullout without fiber rupturing.

Linked Atlas nodes

• 02_concepts/strain_hardening_criteria.md
• 02_concepts/flaw_design.md
• 02_concepts/fiber_bridging_law.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/matrix_fracture_toughness.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).
• Demonstrates a novel physical processing pathway to satisfy Victor Li's PSH energy criterion ($J_b'/J_{tip} \gg 3$): controlling activator solution temperature alters initial gel condensation thermodynamics, tailoring matrix fracture toughness ($K_m$) to unlock tensile ductilities exceeding 18 %.

Claim-evidence rows to add

Verification status

• PDF preserved: yes (nguyen-2023-micromechanical-and-mineralogy-analyses-on.pdf)
• Text extracted: yes (full_text/nguyen-2023-micromechanical-and-mineralogy-analyses-on_full_text.md)
• DOI verified: yes (10.1016/j.jobe.2023.108093)
• Metadata verified: yes (J. Build. Eng., Vol. 80, 108093, 2023)
• Claim-evidence matrix ready: yes

Cautions

• Cooling pretreatment slightly lowers 28-day compressive strength (from 28.5 MPa to 21.4 MPa) due to slower initial dissolution kinetics.
• Requires precise temperature control of the activator solution prior to batching to achieve reproducible mechanical properties.