Nematollahi et al. (2015) — Strain Hardening Behavior of Engineered Geopolymer Composites: Effects of the Activator Combination
Citation
Nematollahi, B., Sanjayan, J., & Shaikh, F. U. A. (2015). Strain hardening behavior of engineered geopolymer composites: Effects of the activator combination. Journal of The Australian Ceramic Society, 51(1), 54–60.
- Atlas layer: core
- Related Victor Li book chapter: Chapter 4: Pseudo Strain-Hardening Criteria & Chapter 7: PVA Fibers & Chapter 9: Green ECC (Fly Ash Geopolymer Systems, pp. 307–342)
- Source PDF:
nematollahi-2015-strain-hardening-behavior-of-engineered-geopolymer.pdf - Extracted text:
full_text/nematollahi-2015-strain-hardening-behavior-of-engineered-geopolymer_full_text.md - Source note:
source_notes/nematollahi-2015-strain-hardening-behavior-of-engineered-geopolymer_source_note.md
Why this paper matters
A foundational study providing direct uniaxial tensile proof of pseudo strain-hardening in Class F fly ash EGC, establishing that sodium-based activators (8 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$) achieve 4.3 % direct tensile strain capacity and 50.5 MPa compressive strength, substantially outperforming potassium-based systems (2.8 % strain, 33.2 MPa).
Main contribution
- Synthesizes 100 % cement-free Engineered Geopolymer Composites (EGC) using Class F fly ash, fine silica sand, and 2.0 vol. % PVA fibers.
- Evaluates the effect of cation species ($\text{Na}^+$ vs. $\text{K}^+$) in liquid activator combinations on fresh workability, density, compressive strength, and uniaxial tensile strain-hardening.
- Discovers that
EGC-Na(8 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$, $M_s = 2.0$) develops superior direct tensile ductility ($\epsilon_u = 4.30\%$), ultimate tensile strength ($\sigma_u = 4.70\text{ MPa}$), and compressive strength ($f_c = 50.5\text{ MPa}$). - Contrasts this with
EGC-K(8 M $\text{KOH} + \text{K}_2\text{SiO}_3$, $M_s = 2.23$), which achieves lower ductility ($\epsilon_u = 2.80\%$) and compressive strength ($f_c = 33.2\text{ MPa}$) due to lower silicate dissolution and larger hydrated cation radius. - Confirms saturated multiple cracking with fine crack widths under uniaxial tension in zero-cement geopolymer matrices.
Evidence summary
- Matrix Composition: 100 % Class F Fly Ash ($64.4\%\ \text{SiO}2, 26.2\%\ \text{Al}_2\text{O}_3, 1.4\%\ \text{CaO}$), silica sand ($d, S/B = 0.30$).} = 150\ \mu\text{m
- Fiber: 2.0 vol. % oiled PVA fibers ($l_f = 8\text{ mm}, d_f = 40\ \mu\text{m}, \sigma_f = 1600\text{ MPa}, E_f = 41\text{ GPa}$, 1.2 wt% oil coating).
- Curing: 60 °C for 24 hours in sealed molds.
- Uniaxial Tensile & Compressive Benchmarks:
EGC-Na: Compressive strength $f_c = 50.5\text{ MPa}$; First crack tensile strength $\sigma_{fc} = 3.10\text{ MPa}$; Ultimate tensile strength $\sigma_u = 4.70\text{ MPa}$; Ultimate tensile strain $\epsilon_u = \mathbf{4.30\%}$.EGC-K: Compressive strength $f_c = 33.2\text{ MPa}$; First crack tensile strength $\sigma_{fc} = 2.40\text{ MPa}$; Ultimate tensile strength $\sigma_u = 3.40\text{ MPa}$; Ultimate tensile strain $\epsilon_u = \mathbf{2.80\%}$.
Linked Atlas nodes
02_concepts/strain_hardening_criteria.md02_concepts/fiber_bridging_law.md04_material_systems/geopolymer_ecc.md04_material_systems/green_ecc.md04_material_systems/pva_ecc.md05_experiments/direct_tensile_test.md02_concepts/circular_economy_materials.md
Relationship to Victor Li book
- Extends Victor Li (2019) Chapter 4 (PSH Criteria), Chapter 7 (PVA Fiber Mechanics), and Chapter 9 (Green ECC).
- Validates the feasibility of achieving Victor Li's PSH strain-hardening ($\epsilon_u > 4\%$) under pure uniaxial tension in 100 % cement-free, coal fly ash-based geopolymer matrices.
Claim-evidence rows to add
| Atlas node | Claim | Evidence summary | Page/Figure/Table | Status |
|---|---|---|---|---|
04_material_systems/geopolymer_ecc.md |
Sodium-activated fly ash PVA-EGC achieves 4.3 % direct tensile strain capacity and 50.5 MPa compressive strength | JSCE direct uniaxial dogbone tensile tests and ASTM cube compression | Section 3, Fig. 3 & 4, Table 2 | verified_from_pdf |
04_material_systems/pva_ecc.md |
Na-based activators deliver superior tensile strength and strain capacity compared to K-based activators in fly ash EGC | Comparative uniaxial tension testing of EGC-Na vs. EGC-K | Section 3.2, Fig. 4, Table 2 | verified_from_pdf |
Verification status
- PDF preserved: yes (
nematollahi-2015-strain-hardening-behavior-of-engineered-geopolymer.pdf) - Text extracted: yes (
full_text/nematollahi-2015-strain-hardening-behavior-of-engineered-geopolymer_full_text.md) - Metadata verified: yes (J. Aust. Ceram. Soc., Vol. 51, No. 1, pp. 54–60, 2015)
- Claim-evidence matrix ready: yes
Cautions
- Uniaxial dogbone alignment is critical; eccentric gripping can mask true strain-hardening capacity.
- Class F fly ash requires thermal activation ($60\ ^\circ\text{C}$); without heat curing, setting and strength gain are substantially delayed.