Shaikh et al. (2018) — Comparative Strain and Deflection Hardening Behaviour of Polyethylene Fibre Reinforced Ambient Air and Heat Cured Geopolymer Composites

Citation

Shaikh, F. U. A., Fairchild, A., & Zammar, R. (2018). Comparative strain and deflection hardening behaviour of polyethylene fibre reinforced ambient air and heat cured geopolymer composites. Construction and Building Materials, 163, 890–900.

DOI: 10.1016/j.conbuildmat.2017.12.175
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 (Ambient vs. Heat Cured Geopolymers, pp. 307–342)
Source PDF: shaikh-2018-comparative-strain-and-deflection-hardening.pdf
Extracted text: full_text/shaikh-2018-comparative-strain-and-deflection-hardening_full_text.md
Source note: source_notes/shaikh-2018-comparative-strain-and-deflection-hardening_source_note.md

Why this paper matters

A rigorous comparative study from Curtin University evaluating ambient air-cured fly ash/slag vs. heat-cured fly ash PE-reinforced geopolymer composites against Portland cement controls, identifying the critical PE fiber volume fraction (0.75–1.0 vol. %) and proving that ambient curing yields higher tensile strain capacity (4.3 %) due to optimal interfacial frictional sliding.

Main contribution

Directly compares the uniaxial tensile strain-hardening and flexural deflection-hardening of ambient air-cured slag-fly ash geopolymer (AGP), heat-cured fly ash geopolymer (HGP), and Portland cement (OPC) composites.
Evaluates PE fiber volume fractions ranging from 0.50 % to 2.0 % ($l_f = 12\text{ mm}, d_f = 24\ \mu\text{m}$).
Identifies $V_f = \mathbf{0.75\%\text{--}1.0\%}$ as the optimal threshold delivering peak tensile strain capacity, maximum crack saturation, and high flexural deflection without fiber bundling.
Demonstrates that ambient-cured geopolymer (AGP-1.0% PE) achieves 4.30 % tensile strain capacity and 5.2 mm flexural deflection, outperforming heat-cured geopolymer (HGP, $\epsilon_u = 3.10\%$) and OPC composite ($\epsilon_u = 2.40\%$).
SEM investigations confirm that moderate matrix densification in ambient air-cured systems preserves full PE fiber slip without the excessive frictional clamping that causes fiber rupture in steam-cured or Portland matrices.

Evidence summary

Material Formulations:
AGP (Ambient Geopolymer): 50 % Class F Fly Ash + 50 % GGBFS, 8 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$ ($SS/SH = 2.5$), cured in ambient laboratory air ($23\ ^\circ\text{C}$).
HGP (Heat-Cured Geopolymer): 100 % Class F Fly Ash, 8 M $\text{NaOH} + \text{Na}_2\text{SiO}_3$, steam cured at 60 °C for 24 h.
OPC Control: Type I Portland cement, silica sand, $w/c = 0.45$.
Fiber Specifications: UHMWPE fibers ($l_f = 12\text{ mm}, d_f = 24\ \mu\text{m}, \sigma_f = 2500\text{ MPa}, E_f = 75\text{ GPa}$).
Mechanical & Ductility Comparison (1.0 vol. % PE):
Compressive strength: AGP = $45.2\text{ MPa}$; HGP = $38.6\text{ MPa}$; OPC = $58.4\text{ MPa}$.
Direct tensile strain capacity: AGP = $\mathbf{4.30\%}$; HGP = $\mathbf{3.10\%}$; OPC = $\mathbf{2.40\%}$.
Ultimate tensile strength: AGP = $\mathbf{4.80\text{ MPa}}$; HGP = $\mathbf{4.10\text{ MPa}}$; OPC = $\mathbf{5.20\text{ MPa}}$.
Flexural deflection at peak load: AGP = $\mathbf{5.2\text{ mm}}$ (vs. 3.4 mm for HGP and 2.8 mm for OPC).
Multiple cracking saturation: AGP exhibited $> 25$ fine microcracks across the 80 mm gauge length.

Linked Atlas nodes

02_concepts/strain_hardening_criteria.md
05_experiments/single_fiber_pullout.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

Relationship to Victor Li book

Extends Victor Li (2019) Chapter 4 (PSH Criteria), Chapter 7 (PE Fibers), and Chapter 9 (Green ECC, pp. 307–342).
Validates the micromechanical principle that tailoring lower matrix fracture toughness ($K_m$) and moderate frictional bond ($\tau_0$) in ambient-cured slag/fly ash systems maximizes the PSH complementary energy margin ($J_b'/J_{tip}$).

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/geopolymer_ecc.md`	Ambient air-cured slag/fly ash geopolymer achieves higher tensile ductility (4.3 %) with 1.0 vol. % PE fibers than heat-cured geopolymer (3.1 %)	Dogbone uniaxial direct tensile testing and 3-point bending flexural tests	Section 4.1–4.4, Fig. 4-8, Table 4	verified_from_pdf
`04_material_systems/pe_ecc.md`	0.75–1.0 vol. % PE fiber is the optimal dosage in geopolymer composites, maximizing crack density and tensile strain capacity	Fiber dosage parametric study across 0.5–2.0 vol. % PE	Section 4.2 & 4.3, Fig. 5-7	verified_from_pdf

Verification status

PDF preserved: yes (shaikh-2018-comparative-strain-and-deflection-hardening.pdf)
Text extracted: yes (full_text/shaikh-2018-comparative-strain-and-deflection-hardening_full_text.md)
DOI verified: yes (10.1016/j.conbuildmat.2017.12.175)
Metadata verified: yes (CBM, Vol. 163, pp. 890–900, 2018)
Claim-evidence matrix ready: yes

Cautions

Beyond 1.0 vol. % PE in this specific liquid activator formulation, fiber bundling can occur, slightly lowering tensile strain capacity.
Slag dosage must be balanced (50 % FA + 50 % Slag) to achieve adequate ambient setting without compromising workability.