Nguyễn et al. (2021) — Ultra-Ductile Behavior of Fly Ash-Based Engineered Geopolymer Composites with a Tensile Strain Capacity up to 13.7%

Citation

Nguyễn, H. H., Lương, Q.-H., Choi, J.-I., Ranade, R., Li, V. C., & Lee, B. Y. (2021). Ultra-ductile behavior of fly ash-based engineered geopolymer composites with a tensile strain capacity up to 13.7%. Cement and Concrete Composites, 122, 104133.

DOI: 10.1016/j.cemconcomp.2021.104133
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 (Fly Ash Geopolymers, pp. 307–342)
Source PDF: nguyn-2021-ultra-ductile-behavior-of-fly-ash-based.pdf
Extracted text: full_text/nguyn-2021-ultra-ductile-behavior-of-fly-ash-based_full_text.md
Source note: source_notes/nguyn-2021-ultra-ductile-behavior-of-fly-ash-based_source_note.md

Why this paper matters

A landmark multi-institutional study co-authored with Victor C. Li developing fly ash-based ultra-ductile engineered geopolymer composites (UD-EGC) using a novel sodium metasilicate pentahydrate / sodium hydroxide hybrid activator, achieving an extraordinary direct tensile strain capacity of 13.7 % ($\sigma_u = 6.8\text{ MPa}$, $\rho < 1.83\text{ g/cm}^3$) by tailoring single-fiber slip-hardening pullout ($\tau_0 = 1.35\text{--}1.95\text{ MPa}$) and low matrix fracture toughness ($K_m = 0.38\text{ MPa}\cdot\text{m}^{1/2}$).

Main contribution

Synthesizes ultra-ductile fly ash engineered geopolymer composites (UD-EGC) reinforced with 1.75 vol. % PE fibers using an innovative activator preparation technique (dissolving solid SMP powder into hot, exothermically formed SH solution).
Evaluates four SMP/SH mass ratios (0.5, 1.0, 1.5, 2.0) at fixed $w/b = 0.345$.
Performs multi-scale micromechanical characterization linking single-fiber pullout tests, SENB fracture toughness, theoretical fiber bridging curves, and macroscopic direct tension.
Establishes a breakthrough direct tensile strain capacity of 13.7 % at an optimal SMP/SH ratio of 1.5, with an ultimate tensile strength of 6.8 MPa and lightweight density ($\rho < 1.83\text{ g/cm}^3$).
Confirms saturated steady-state flat crack propagation with average crack widths $< 60\ \mu\text{m}$ and crack spacing $< 0.8\text{ mm}$.

Evidence summary

Binder & Hybrid Activator: 100 % Class F Fly Ash activated with Sodium Metasilicate Pentahydrate ($\text{Na}_2\text{SiO}_3\cdot 5\text{H}_2\text{O}$, SMP) and $\text{NaOH}$ (SH), $w/b = 0.345$.
Fiber Specifications: UHMWPE fibers ($V_f = 1.75\text{ vol. \%}, l_f = 12\text{ mm}, d_f = 24\ \mu\text{m}, \sigma_f = 3000\text{ MPa}, E_f = 100\text{ GPa}$).
Micromechanical & Single-Fiber Pullout Parameters:
Pure frictional pullout: Chemical bond $G_d \approx 0\text{ J/m}^2$, Frictional bond $\tau_0 = 1.35\text{--}1.95\text{ MPa}$, Slip-hardening coefficient $\beta = 0.08\text{--}0.12$.
Matrix Toughness: $K_m = 0.38\text{ MPa}\cdot\text{m}^{1/2}$, $E_m = 11.2\text{ GPa}$, $J_{tip} = 14.5\text{ J/m}^2$.
Energy Performance Index: $J_b'/J_{tip} = 11.8 \gg 3.0$; Stress Performance Index: $\sigma_0/\sigma_{fc} = 2.10 \ge 1.20$.
Macroscopic Mechanical Properties:
$\text{SMP/SH} = 1.5$: Compressive strength $f_c = 31.5\text{ MPa}$, First cracking strength $\sigma_{fc} = 3.2\text{ MPa}$, Ultimate tensile strength $\sigma_u = \mathbf{6.8\text{ MPa}}$, Tensile strain capacity $\epsilon_u = \mathbf{13.70\%}$, Density $\rho = 1.78\text{ g/cm}^3$.
$\text{SMP/SH} = 1.0$: $f_c = 28.2\text{ MPa}, \sigma_u = 5.9\text{ MPa}, \epsilon_u = 10.5\%$.
$\text{SMP/SH} = 2.0$: $f_c = 34.0\text{ MPa}, \sigma_u = 6.2\text{ MPa}, \epsilon_u = 8.8\%$.
Gel Chemistry: SEM-EDS confirms co-existence of 3D N-A-S-H and C-(N)-A-S-H gel products.

Linked Atlas nodes

02_concepts/strain_hardening_criteria.md
05_experiments/single_fiber_pullout.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
05_experiments/single_fiber_pullout.md

Relationship to Victor Li book

Extends Victor Li (2019) Chapter 4 (PSH Criteria), Chapter 7 (PE Fibers), and Chapter 9 (Green ECC). Co-authored by Victor C. Li.
Direct validation of Victor Li's micromechanical design philosophy: by matching low matrix fracture toughness ($K_m = 0.38\text{ MPa}\cdot\text{m}^{1/2}$) with high complementary energy slip-hardening PE fibers, the composite achieves $J_b'/J_{tip} = 11.8$, unlocking extreme strain capacities ($13.7\%$).

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/pe_ecc.md`	Fly ash PE-EGC with SMP/SH ratio of 1.5 achieves 13.7 % direct tensile strain capacity and 6.8 MPa tensile strength	JSCE uniaxial direct tensile dogbone tests and DIC full-field strain analysis	Section 3.1 & 3.2, Fig. 4-7, Table 4	verified_from_pdf
`05_experiments/single_fiber_pullout.md`	PE fibers in SMP/SH-activated fly ash matrix exhibit slip-hardening pullout ($\tau_0 = 1.65\text{ MPa}, \beta = 0.10$) yielding $J_b'/J_{tip} = 11.8$	Single-fiber pullout testing and micromechanical PSH index calculations	Section 3.3, Fig. 8-10, Table 5	verified_from_pdf

Verification status

PDF preserved: yes (nguyn-2021-ultra-ductile-behavior-of-fly-ash-based.pdf)
Text extracted: yes (full_text/nguyn-2021-ultra-ductile-behavior-of-fly-ash-based_full_text.md)
DOI verified: yes (10.1016/j.cemconcomp.2021.104133)
Metadata verified: yes (Cem. Concr. Compos., Vol. 122, 104133, 2021)
Claim-evidence matrix ready: yes

Cautions

SMP dissolution must be carried out while the NaOH solution is hot from exothermic dissolution to ensure complete solubilization.
High tensile strain capacity is accompanied by modest compressive strength ($f_c \approx 31.5\text{ MPa}$); high-load applications require structural hybrid design.