Shaikh (2013) — Deflection Hardening Behaviour of Short Fibre Reinforced Fly Ash Based Geopolymer Composites

Citation

Shaikh, F. U. A. (2013). Deflection hardening behaviour of short fibre reinforced fly ash based geopolymer composites. Materials & Design, 50, 674–682.

DOI: 10.1016/j.matdes.2013.03.063
Atlas layer: core
Related Victor Li book chapter: Chapter 4: Pseudo Strain-Hardening Criteria & Chapter 7: Alternative Reinforcing Fibers (PVA & Steel Hybrids) & Chapter 9: Green ECC (Deflection-Hardening Geopolymer Composites, pp. 307–342)
Source PDF: shaikh-2013-deflection-hardening-behaviour-of-short-fibre.pdf
Extracted text: full_text/shaikh-2013-deflection-hardening-behaviour-of-short-fibre_full_text.md
Source note: source_notes/shaikh-2013-deflection-hardening-behaviour-of-short-fibre_source_note.md

Why this paper matters

An early milestone paper from Curtin University demonstrating deflection-hardening and multiple cracking in 100 % fly ash-based ductile fiber-reinforced geopolymer composites (DFRGC), comparing mono-PVA, mono-steel, and hybrid steel-PVA systems against Portland cement controls under 4-point flexure.

Main contribution

Develops Ductile Fibre Reinforced Geopolymer Composites (DFRGC) utilizing Class F fly ash activated by 8 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$ solutions.
Evaluates mono-steel (2.0 vol. %), mono-PVA (2.0 vol. %), and hybrid steel-PVA (1.0 % + 1.0 %) fiber reinforcement.
Investigates the effects of maximum sand size ($0.60\text{ mm}$ vs. $1.18\text{ mm}$) and sand/binder ratios ($S/B = 0.50$ vs. 0.75) on flexural toughness.
Demonstrates that DFRGC achieves ASTM C1018 flexural toughness indices of $I_{20} > 20$ and modulus of rupture up to 14.8 MPa, matching or exceeding Portland-based DFRCC.
Confirms through SEM analysis that PVA fibers exhibit strong chemical/mechanical bonding in alkali-activated fly ash matrices without fiber deterioration.

Evidence summary

Material Matrix: Class F Fly Ash (Collie Power Station, WA), activated by $\text{Na}_2\text{SiO}_3$ ($14.7\%\ \text{Na}_2\text{O}, 29.4\%\ \text{SiO}_2$) + 8 M $\text{NaOH}$ solution ($\text{activator}/FA = 0.45, SS/SH = 2.5$), steam cured at 60 °C for 24 h.
Fiber Types:
PVA Fibers: Kuraray K-II REC15, $l_f = 8\text{ mm}, d_f = 40\ \mu\text{m}, \sigma_f = 1600\text{ MPa}, E_f = 41\text{ GPa}$.
Micro Steel Fibers: $l_f = 13\text{ mm}, d_f = 200\ \mu\text{m}, \sigma_f = 2200\text{ MPa}, E_f = 200\text{ GPa}$.
Total Fiber Volume: $V_f = 2.0\text{ vol. \%}$.
Four-Point Bending Results ($20 \times 75 \times 300\text{ mm}$ prisms):
PVA-DFRGC ($S/B = 0.50$, sand $< 0.6\text{ mm}$): Flexural strength $\text{MOR} = \mathbf{11.2\text{ MPa}}$, peak deflection $\delta_p = \mathbf{3.6\text{ mm}}$, ASTM toughness index $I_{20} = 24.5$.
Hybrid ST-PVA DFRGC: Peak flexural strength $\text{MOR} = \mathbf{14.8\text{ MPa}}$, peak deflection $\delta_p = 2.8\text{ mm}$.
Steel-DFRGC: Flexural strength $\text{MOR} = 13.5\text{ MPa}$, $\delta_p = 2.1\text{ mm}$.
Aggregate Optimization: Reducing sand particle size to $< 0.60\text{ mm}$ and limiting $S/B$ to 0.50 reduces matrix fracture energy ($J_{tip}$), significantly promoting saturated multiple cracking.

Linked Atlas nodes

02_concepts/strain_hardening_criteria.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), Chapter 7 (PVA and Steel Fibers), and Chapter 9 (Green ECC, pp. 307–342).
Validates that the PSH aggregate-size suppression rule (finer sand and lower sand-to-binder ratio lowers $K_m$) applies directly to alkali-activated geopolymer composites.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/geopolymer_ecc.md`	Fly ash-based PVA and hybrid ST-PVA geopolymer composites achieve deflection hardening with MOR up to 14.8 MPa and $I_{20} > 20$	4-point bending prism tests on 20x75x300 mm specimens	Section 4.1–4.3, Fig. 3-6, Table 4	verified_from_pdf
`02_concepts/strain_hardening_criteria.md`	Reducing maximum sand size to 0.60 mm and $S/B$ to 0.50 enhances multiple cracking and flexural ductility in geopolymer composites	Aggregate size comparison and flexural load-deflection curve analysis	Section 4.2, Fig. 4 & 5	verified_from_pdf

Verification status

PDF preserved: yes (shaikh-2013-deflection-hardening-behaviour-of-short-fibre.pdf)
Text extracted: yes (full_text/shaikh-2013-deflection-hardening-behaviour-of-short-fibre_full_text.md)
DOI verified: yes (10.1016/j.matdes.2013.03.063)
Metadata verified: yes (Mater. Des., Vol. 50, pp. 674–682, 2013)
Claim-evidence matrix ready: yes

Cautions

Coarse sand ($> 1.18\text{ mm}$) increases matrix flaw sizes and matrix toughness, suppressing multiple cracking in PVA geopolymer systems.
Heat curing (60 °C for 24 h) is necessary for Class F fly ash geopolymers without slag addition.