Nematollahi et al. (2014) — Comparative Deflection Hardening Behavior of Short Fiber Reinforced Geopolymer Composites

Citation

Nematollahi, B., Sanjayan, J., & Shaikh, F. U. A. (2014). Comparative deflection hardening behavior of short fiber reinforced geopolymer composites. Construction and Building Materials, 70, 54–64.

DOI: 10.1016/j.conbuildmat.2014.07.085
Atlas layer: foundational
Related Victor Li book chapter: Chapter 4: Pseudo Strain-Hardening Criteria (Matrix Fracture Toughness $K_m$ and $J_{tip}$) & Chapter 7: PVA Fibers & Chapter 9: Green ECC (Fly Ash Geopolymer Systems)
Source PDF: nematollahi-2014-comparative-deflection-hardening-behavior-of-1.pdf
Extracted text: full_text/nematollahi-2014-comparative-deflection-hardening-behavior-of-1_full_text.md
Source note: source_notes/nematollahi-2014-comparative-deflection-hardening-behavior-of-1_source_note.md

Why this paper matters

A foundational study systematically comparing four alkali-activator combinations (Na-silicate, K-silicate, solid Ca-activator) in Class F fly ash matrices reinforced with 2.0 vol. % PVA fibers, establishing that 8 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$ ($M_s = 2.0$) produces the optimal matrix fracture toughness ($K_m = 0.53\text{ MPa}\cdot\text{m}^{1/2}$) and superior deflection-hardening ductility ($\delta_p = 4.2\text{ mm}$, MOR = 10.8 MPa).

Main contribution

Evaluates matrix and composite fracture properties across four distinct activator formulations: 1. Na-1: 8.0 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$ ($M_s = 2.0$, mass ratio 1:2.5) 2. Na-2: 8.0 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$ ($M_s = 2.0$, mass ratio 1:1.5) 3. K-1: 8.0 M $\text{KOH} + \text{K}_2\text{SiO}_3$ 4. Ca-1: Solid $\text{Ca(OH)}_2 + \text{Na}_2\text{SO}_4$ powder activator
Measures notched-beam fracture toughness ($K_m$), elastic modulus ($E_m$), and calculates crack tip fracture energy $J_{tip} = K_m^2/E_m$.
Investigates 4-point flexural deflection-hardening, crack multiplicity, and composite toughness in 2.0 vol. % PVA fiber composites alongside a counterpart OPC-DFRCC.
Proves that DFRGC-Na-1 delivers the optimal balance of compressive strength ($f_c = 44.8\text{ MPa}$), matrix toughness ($K_m = 0.53\text{ MPa}\cdot\text{m}^{1/2}$), modulus of rupture (MOR = 10.8 MPa), and midspan deflection capacity ($\delta_p = 4.2\text{ mm}$, deflection ductility index $\delta_p/\delta_{cr} = 9.8$).

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 ($l_f = 8\text{ mm}, d_f = 40\ \mu\text{m}, \sigma_f = 1600\text{ MPa}, E_f = 41\text{ GPa}$, oiling 1.2 wt%).
Curing: Heat cured at 60 °C for 24 hours, then ambient stored.
Matrix & Composite Properties:
DFRGC-Na-1: $f_c = 44.8\text{ MPa}$, $E_m = 12.8\text{ GPa}$, $K_m = 0.53\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 21.9\text{ J/m}^2$, $\text{MOR} = 10.8\text{ MPa}$, $\delta_p = 4.2\text{ mm}$.
DFRGC-Na-2: $f_c = 36.2\text{ MPa}$, $E_m = 10.5\text{ GPa}$, $K_m = 0.44\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 18.4\text{ J/m}^2$, $\text{MOR} = 8.5\text{ MPa}$, $\delta_p = 3.6\text{ mm}$.
DFRGC-K-1: $f_c = 28.5\text{ MPa}$, $E_m = 8.9\text{ GPa}$, $K_m = 0.38\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 16.2\text{ J/m}^2$, $\text{MOR} = 6.9\text{ MPa}$, $\delta_p = 2.8\text{ mm}$.
DFRGC-Ca-1: $f_c = 22.4\text{ MPa}$, $E_m = 7.2\text{ GPa}$, $K_m = 0.32\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 14.2\text{ J/m}^2$, $\text{MOR} = 5.4\text{ MPa}$, $\delta_p = 2.1\text{ mm}$.
OPC-DFRCC: $f_c = 48.2\text{ MPa}$, $E_m = 18.5\text{ GPa}$, $K_m = 0.68\text{ MPa}\cdot\text{m}^{1/2}$, $J_{tip} = 25.0\text{ J/m}^2$, $\text{MOR} = 9.2\text{ MPa}$, $\delta_p = 3.1\text{ mm}$.

Linked Atlas nodes

02_concepts/strain_hardening_criteria.md
02_concepts/flaw_design.md
04_material_systems/geopolymer_ecc.md
04_material_systems/green_ecc.md
04_material_systems/pva_ecc.md
02_concepts/matrix_fracture_toughness.md
05_experiments/flexural_testing.md

Relationship to Victor Li book

Extends Victor Li (2019) Chapter 4 (PSH Matrix Toughness Criteria) and Chapter 9 (Green ECC / Fly Ash Geopolymers).
Provides systematic experimental verification of how alkaline activator composition directly tunes matrix fracture toughness ($K_m$) and crack tip energy ($J_{tip}$), satisfying the $J_b'/J_{tip}$ condition for saturated deflection-hardening in cement-free geopolymer matrices.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/geopolymer_ecc.md`	Sodium silicate/hydroxide activated fly ash PVA composites achieve superior flexural MOR (10.8 MPa) and deflection ductility over K- and Ca-activated systems	Four-point bending tests across 4 activator formulations	Section 3.3, Fig. 6-9, Table 4	verified_from_pdf
`02_concepts/flaw_design.md`	Fly ash geopolymer matrix fracture toughness ($K_m = 0.32\text{--}0.53\text{ MPa}\cdot\text{m}^{1/2}$) is lower than Portland cement ($0.68\text{ MPa}\cdot\text{m}^{1/2}$), favoring the PSH energy criterion	ASTM E399 single-edge notched beam fracture testing	Section 3.2, Fig. 4 & 5, Table 3	verified_from_pdf

Verification status

PDF preserved: yes (nematollahi-2014-comparative-deflection-hardening-behavior-of-1.pdf)
Text extracted: yes (full_text/nematollahi-2014-comparative-deflection-hardening-behavior-of-1_full_text.md)
DOI verified: yes (10.1016/j.conbuildmat.2014.07.085)
Metadata verified: yes (CBM, Vol. 70, pp. 54–64, 2014)
Claim-evidence matrix ready: yes

Cautions

Low-calcium fly ash geopolymer systems in this paper require moderate heat activation ($60\ ^\circ\text{C}$ for 24 hours); ambient curing requires blending with slag or calcium-rich precursors.
K-based activators exhibit lower mechanical strength and lower fracture toughness than Na-based activators at identical molarity.