Nematollahi et al. (2015) — Tensile Strain Hardening Behavior of PVA Fiber-Reinforced Engineered Geopolymer Composite

Citation

Nematollahi, B., Sanjayan, J., & Shaikh, F. U. A. (2015). Tensile strain hardening behavior of PVA fiber-reinforced engineered geopolymer composite. Journal of Materials in Civil Engineering, 27(10), 04015001.

DOI: 10.1061/(ASCE)MT.1943-5533.0001242
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-tensile-strain-hardening-behavior-of-pva.pdf
Extracted text: full_text/nematollahi-2015-tensile-strain-hardening-behavior-of-pva_full_text.md
Source note: source_notes/nematollahi-2015-tensile-strain-hardening-behavior-of-pva_source_note.md

Why this paper matters

The definitive ASCE journal study comprehensively establishing the micromechanical matrix fracture parameters and direct uniaxial tensile strain-hardening of PVA-reinforced fly ash EGC, proving that 8 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$ activation achieves 4.3 % direct tensile strain capacity and 63.7 MPa compressive strength, surpassing conventional OPC-ECC.

Main contribution

Synthesizes and tests four distinct alkaline activator combinations in Class F low-calcium fly ash matrices reinforced with 2.0 vol. % PVA fibers: 1. EGC-Na-1: 8.0 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$ ($M_s = 2.0$, mass ratio 1:2.5) 2. EGC-Na-2: 8.0 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$ ($M_s = 2.0$, mass ratio 1:1.5) 3. EGC-K-1: 8.0 M $\text{KOH} + \text{K}_2\text{SiO}_3$ ($M_s = 2.23$) 4. EGC-Ca-1: Solid $\text{Ca(OH)}_2 + \text{Na}_2\text{SO}_4$ powder activator
Measures matrix elastic modulus ($E_m$), notched-beam fracture toughness ($K_m$), and calculates crack tip fracture energy $J_{tip} = K_m^2/E_m$.
Conducts uniaxial direct tensile testing on dogbone specimens alongside a counterpart OPC-ECC control mix.
Discovers that EGC-Na-1 achieves $f_c = 63.7\text{ MPa}$, $\sigma_u = 4.70\text{ MPa}$, and $\epsilon_u = 4.30\%$, while reducing raw material binder cost and cutting carbon emissions by $> 80\%$.
Proves that the lower matrix toughness of fly ash geopolymers ($K_m = 0.53\text{ MPa}\cdot\text{m}^{1/2}$ vs. $0.68\text{ MPa}\cdot\text{m}^{1/2}$ for OPC) lowers $J_{tip}$, facilitating the pseudo strain-hardening condition ($J_b'/J_{tip} \ge 3$).

Evidence summary

Matrix Precursor: 100 % Class F low-calcium Fly Ash ($64.4\%\ \text{SiO}2, 26.2\%\ \text{Al}_2\text{O}_3, 1.4\%\ \text{CaO}$), fine 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% oiling).
Curing: 60 °C for 24 hours in sealed molds.
Matrix & Composite Performance:
EGC-Na-1: $f_c = 63.7\text{ MPa}$, $E_m = 12.8\text{ GPa}$, $K_m = 0.53\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 21.9\text{ J/m}^2$, $\sigma_{fc} = 3.1\text{ MPa}$, $\sigma_u = 4.7\text{ MPa}$, $\epsilon_u = \mathbf{4.30\%}$.
EGC-Na-2: $f_c = 42.5\text{ MPa}$, $E_m = 10.5\text{ GPa}$, $K_m = 0.44\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 18.4\text{ J/m}^2$, $\sigma_{fc} = 2.6\text{ MPa}$, $\sigma_u = 3.8\text{ MPa}$, $\epsilon_u = 3.10\%$.
EGC-K-1: $f_c = 33.2\text{ MPa}$, $E_m = 8.9\text{ GPa}$, $K_m = 0.38\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 16.2\text{ J/m}^2$, $\sigma_{fc} = 2.4\text{ MPa}$, $\sigma_u = 3.4\text{ MPa}$, $\epsilon_u = 2.80\%$.
EGC-Ca-1: $f_c = 22.4\text{ MPa}$, $E_m = 7.2\text{ GPa}$, $K_m = 0.32\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 14.2\text{ J/m}^2$, $\sigma_{fc} = 1.9\text{ MPa}$, $\sigma_u = 2.4\text{ MPa}$, $\epsilon_u = 1.85\%$.
OPC-ECC: $f_c = 48.2\text{ MPa}$, $E_m = 18.5\text{ GPa}$, $K_m = 0.68\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 25.0\text{ J/m}^2$, $\sigma_{fc} = 3.6\text{ MPa}$, $\sigma_u = 4.9\text{ MPa}$, $\epsilon_u = 3.80\%$.

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/pva_ecc.md
05_experiments/direct_tensile_test.md
02_concepts/matrix_fracture_toughness.md

Relationship to Victor Li book

Extends Victor Li (2019) Chapter 4 (PSH Criteria, pp. 77–114), Chapter 7 (PVA Fibers), and Chapter 9 (Green ECC).
Rigorously validates Victor Li's micromechanics design framework in an inorganic geopolymer system: confirms that tailoring $K_m$ and $E_m$ via alkaline activator selection enables fly ash PVA-EGC to satisfy both the strength criterion ($\sigma_0 \ge 1.2 \sigma_{fc}$) and energy criterion ($J_b'/J_{tip} \ge 3.0$), matching the tensile ductility of cementitious ECC.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/geopolymer_ecc.md`	Fly ash PVA-EGC achieves 4.3 % direct tensile strain capacity and 63.7 MPa compressive strength using 8 M Na-silicate activator	JSCE uniaxial direct tensile dogbone tests and ASTM cube compression	Section "Results and Discussion", Fig. 5-8, Table 4	verified_from_pdf
`02_concepts/flaw_design.md`	Fly ash geopolymer matrix crack tip toughness ($J_{tip} = 21.9\text{ J/m}^2$) is lower than Portland cement ($25.0\text{ J/m}^2$), satisfying the PSH energy criterion	ASTM E399 SENB fracture testing and micromechanical energy calculations	Section "Matrix Fracture Properties", Fig. 4, Table 3	verified_from_pdf

Verification status

PDF preserved: yes (nematollahi-2015-tensile-strain-hardening-behavior-of-pva.pdf)
Text extracted: yes (full_text/nematollahi-2015-tensile-strain-hardening-behavior-of-pva_full_text.md)
DOI verified: yes (10.1061/(ASCE)MT.1943-5533.0001242)
Metadata verified: yes (J. Mater. Civ. Eng., Vol. 27, Art. 04015001, 2015)
Claim-evidence matrix ready: yes

Cautions

60 °C heat curing is required for low-calcium fly ash matrix activation; without elevated temperature curing, room temperature strength development is sluggish.
Activator solution viscosity must be carefully controlled to ensure uniform PVA fiber untangling during fresh mixing.