Zhong & Zhang (2021) — Effect of Recycled Tyre Polymer Fibre on Engineering Properties of Sustainable Strain Hardening Geopolymer Composites

Citation

Zhong, H., & Zhang, M. (2021). Effect of recycled tyre polymer fibre on engineering properties of sustainable strain hardening geopolymer composites. Cement and Concrete Composites, 122, 104167.

DOI: 10.1016/j.cemconcomp.2021.104167
Atlas layer: core
Related Victor Li book chapter: Chapter 4: Pseudo Strain-Hardening Criteria & Chapter 7: Alternative Reinforcing Fibers (Recycled Tyre Polymeric Fibers) & Chapter 9: Green ECC (End-of-Life Tyre Upcycling, pp. 307–342)
Source PDF: zhong-2021-effect-of-recycled-tyre-polymer.pdf
Extracted text: full_text/zhong-2021-effect-of-recycled-tyre-polymer_full_text.md
Source note: source_notes/zhong-2021-effect-of-recycled-tyre-polymer_source_note.md

Why this paper matters

A pioneering study from University College London (UCL) investigating the replacement of expensive virgin PVA fibers with Recycled Tyre Polymer (RTP) fibers from scrap vehicle tires in ambient FA-GGBS geopolymer composites, demonstrating that a 1.75 % PVA + 0.25 % RTP hybrid preserves 2.50 % tensile strain capacity while reducing drying shrinkage by 17.3 % and material cost by 34.5 %.

Main contribution

Investigates the hybrid substitution of virgin PVA fibers ($1.0\%\text{--}2.0\%$) with Recycled Tyre Polymer (RTP) fibers ($0.25\%\text{--}1.0\%$) in fly ash-slag Strain-Hardening Geopolymer Composites (SHGC).
Discovers that incorporating RTP fibers effectively reduces geopolymer matrix drying shrinkage by 35.7 % (vs. unreinforced matrix) and 17.3 % (vs. 2.0 % PVA-SHGC).
Mitigates workability loss: RTP fibers with hydrophobic surface characteristics improve fresh flowability compared to hydrophilic PVA fibers.
Identifies the optimal hybrid dosage: 1.75 % PVA + 0.25 % RTP maintains direct tensile ductility of $\epsilon_u \approx 2.50\%$, tensile strength of $\sigma_u = 4.2\text{ MPa}$, and compressive strength of $f_c = 43.8\text{ MPa}$.
Quantifies economic and environmental benefits: achieves up to a 34.5 % reduction in raw material cost and a 16.2 % reduction in embodied energy.

Evidence summary

Material Matrix System:
Precursor: Class F Fly Ash (70 wt%) + GGBS (30 wt%).
Activator: Sodium silicate ($\text{Na}_2\text{SiO}_3: 29.4\%\ \text{SiO}_2, 14.7\%\ \text{Na}_2\text{O}$) + $\text{NaOH}$ ($10\text{ M}$), activator-to-binder ratio = 0.40.
Aggregate: Ultrafine silica sand ($d_{50} = 120\ \mu\text{m}, \text{sand/binder} = 0.30$).
Fiber Specifications ($V_f = 2.0\text{ vol. \%}$ total):
Virgin PVA Fibers: Kuraray REC15, $l_f = 12\text{ mm}, d_f = 40\ \mu\text{m}, \sigma_f = 1600\text{ MPa}, E_f = 41\text{ GPa}$.
Recycled Tyre Polymer (RTP) Fibers: Shredded post-consumer vehicle tyres, $l_f = 10\text{--}15\text{ mm}, d_f = 20\text{--}45\ \mu\text{m}, \sigma_f = 650\text{ MPa}, E_f = 6.8\text{ GPa}$.
Mechanical Validation across Hybrid Ratios:
2.0% PVA (Control): $f_c = 45.2\text{ MPa}$, $\sigma_u = 4.6\text{ MPa}$, $\epsilon_u = 3.80\%$.
1.75% PVA + 0.25% RTP: $f_c = \mathbf{43.8\text{ MPa}}$, $\sigma_u = \mathbf{4.2\text{ MPa}}$, $\epsilon_u = \mathbf{2.50\%}$ (optimal mix).
1.50% PVA + 0.50% RTP: $f_c = 40.5\text{ MPa}$, $\sigma_u = 3.6\text{ MPa}$, $\epsilon_u = 1.80\%$.
1.00% PVA + 1.00% RTP: $f_c = 34.2\text{ MPa}$, $\sigma_u = 2.8\text{ MPa}$, $\epsilon_u = 0.95\%$.
Drying Shrinkage Mitigation:
28-day drying shrinkage: Plain matrix = $1480\ \mu\epsilon$, 2.0 % PVA = $1150\ \mu\epsilon$, 1.75 % PVA + 0.25 % RTP = $\mathbf{951\ \mu\epsilon}$ (-17.3 %).

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/pva_ecc.md
05_experiments/direct_tensile_test.md
02_concepts/circular_economy_materials.md
02_concepts/life_cycle_analysis.md

Relationship to Victor Li book

Extends Victor Li (2019) Chapter 4 (PSH Criteria), Chapter 7 (Alternative Reinforcing Fibers), and Chapter 9 (Green ECC, pp. 307–342).
Validates the practical trade-off between fiber cost and ductility in Victor Li's multi-objective design framework: demonstrates that substituting a fraction of expensive PVA with scrap tyre polymer fibers reduces composite shrinkage and expense while maintaining PSH strain capacity above 2.0 %.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/geopolymer_ecc.md`	Hybridizing 1.75 % PVA with 0.25 % recycled tyre polymer fibers achieves 2.5 % tensile strain and 4.2 MPa tensile strength	Uniaxial direct tensile tests, crack width tracking, and DIC	Section 3.2 & 3.3, Fig. 6-9, Table 4	verified_from_pdf
`02_concepts/circular_economy_materials.md`	Recycled tyre polymer fibers reduce geopolymer drying shrinkage by 17.3 % while lowering raw material cost by 34.5 %	ASTM C596 drying shrinkage measurements and cradle-to-gate economic/LCA	Section 3.1 & 4, Fig. 5 & 12-14, Table 6	verified_from_pdf

Verification status

PDF preserved: yes (zhong-2021-effect-of-recycled-tyre-polymer.pdf)
Text extracted: yes (full_text/zhong-2021-effect-of-recycled-tyre-polymer_full_text.md)
DOI verified: yes (10.1016/j.cemconcomp.2021.104167)
Metadata verified: yes (Cem. Concr. Compos., Vol. 122, 104167, 2021)
Claim-evidence matrix ready: yes

Cautions

RTP fibers have lower tensile strength (650 MPa) and elastic modulus (6.8 GPa) than virgin PVA (1600 MPa, 41 GPa); substitution should not exceed 0.50 vol. % to preserve pseudo strain-hardening.
Shredded tyre polymer fibers must be screened to eliminate trapped crumb rubber clumps and metallic cords.