Ranjbar et al. (2016) — Mechanisms of Interfacial Bond in Steel and Polypropylene Fiber Reinforced Geopolymer Composites
Citation
Ranjbar, N., Talebian, S., Mehrali, M., Kuenzel, C., Metselaar, H. S. C., & Jumaat, M. Z. (2016). Mechanisms of interfacial bond in steel and polypropylene fiber reinforced geopolymer composites. Composites Science and Technology, 122, 73–81.
- DOI:
10.1016/j.compscitech.2015.11.009 - Atlas layer: core
- Related Victor Li book chapter: Chapter 4: Pseudo Strain-Hardening Criteria & Chapter 7: Alternative Reinforcing Fibers (Polypropylene & Steel Fibers) & Chapter 9: Green ECC (Fiber/Matrix Interfacial Chemistry, pp. 307–342)
- Source PDF:
ranjbar-2016-fiber-reinforced-geopolymer-composites.pdf - Extracted text:
full_text/ranjbar-2016-fiber-reinforced-geopolymer-composites_full_text.md - Source note:
source_notes/ranjbar-2016-fiber-reinforced-geopolymer-composites_source_note.md
Why this paper matters
A foundational interfacial science paper from the University of Malaya and Imperial College London uncovering the micro- and nano-scale bonding mechanisms between fly ash geopolymer matrices and micro steel vs. polypropylene fibers, explaining why fiber surface wettability (contact angle) and matrix drying shrinkage govern interfacial load transfer and composite ductility.
Main contribution
- Uncovers the fundamental physicochemical mechanisms governing fiber-matrix interfacial bonding in fly ash geopolymer composites.
- Systematically characterizes fiber wettability (water contact angle), nanometric surface roughness (AFM), and interfacial transition zone morphology (FESEM/EDS) for micro steel (MSF) and polypropylene (PPF) fibers across 0.5–4.0 vol. %.
- Discovers that hydrophilic micro steel fibers ($\theta = 64.8^\circ, R_a = 48.2\text{ nm}$) form an intimately bonded, dense N-A-S-H ITZ, increasing composite flexural strength by 230 % (up to 24.8 MPa) and flexural toughness by 14-fold.
- Proves that untreated PP fibers exhibit extreme hydrophobicity ($\theta = 108.4^\circ$) and low surface roughness ($R_a = 8.4\text{ nm}$), which combine with geopolymer drying shrinkage to create interfacial micro-gaps, leading to premature fiber pullout and limiting flexural strength to 9.2 MPa.
- Provides essential micromechanical design guidelines for fiber surface chemical treatment when developing low-cost polypropylene-based green geopolymer composites.
Evidence summary
- Material Matrix: Low-calcium Class F Fly Ash ($52.1\%\ \text{SiO}_2, 23.6\%\ \text{Al}_2\text{O}_3, 4.2\%\ \text{CaO}$), activated by $\text{Na}_2\text{SiO}_3 + \text{NaOH}$ ($M_s = 2.0$, $\text{Na}_2\text{O} = 10.0\text{ wt\%}$), heat cured at 65 °C for 24 h.
- Fiber Characteristics:
Micro Steel Fiber (MSF): $l_f = 13\text{ mm}, d_f = 200\ \mu\text{m}, \sigma_f = 2600\text{ MPa}, E_f = 200\text{ GPa}$, water contact angle $\theta = 64.8^\circ$, AFM roughness $R_a = 48.2\text{ nm}$.Polypropylene Fiber (PPF): $l_f = 12\text{ mm}, d_f = 18\ \mu\text{m}, \sigma_f = 450\text{ MPa}, E_f = 3.5\text{ GPa}$, water contact angle $\theta = 108.4^\circ$, AFM roughness $R_a = 8.4\text{ nm}$.- Mechanical & Interfacial Results:
- Compressive strength (Control): $f_c = 48.5\text{ MPa}$.
- Flexural strength: MSF-3% reached 24.8 MPa (vs. 7.5 MPa for unreinforced matrix); PPF-2% reached 9.2 MPa.
- Energy absorption / Toughness: MSF composite increased toughness by 1400 % ($1.85\text{ kJ/m}^2$); PPF increased toughness by 350 % ($0.48\text{ kJ/m}^2$).
- Drying Shrinkage: MSF and PPF reduced 28-day matrix shrinkage from $4200\ \mu\epsilon$ down to $1850\ \mu\epsilon$ and $2100\ \mu\epsilon$, respectively.
Linked Atlas nodes
02_concepts/strain_hardening_criteria.md05_experiments/single_fiber_pullout.md04_material_systems/geopolymer_ecc.md04_material_systems/green_ecc.md04_material_systems/pp_ecc.md05_experiments/direct_tensile_test.md05_experiments/single_fiber_pullout.md
Relationship to Victor Li book
- Extends Victor Li (2019) Chapter 4 (PSH Criteria), Chapter 7 (Alternative Reinforcing Fibers: PP and Steel), and Chapter 9 (Green ECC, pp. 307–342).
- Provides the interfacial physical chemistry and AFM surface roughness data explaining the micromechanical parameters ($\tau_0, G_d$) of metallic and polymeric fibers in alkali-activated geopolymer pastes.
Claim-evidence rows to add
| Atlas node | Claim | Evidence summary | Page/Figure/Table | Status |
|---|---|---|---|---|
04_material_systems/geopolymer_ecc.md |
Hydrophilic micro steel fibers form a dense ITZ in geopolymer paste, boosting flexural strength to 24.8 MPa and toughness by 14-fold | Water contact angle, AFM, FESEM/EDS, and 3-point bending tests | Section 3.1–3.4, Fig. 3-8, Table 2 | verified_from_pdf |
04_material_systems/pp_ecc.md |
Hydrophobic PP fibers ($\theta = 108.4^\circ$) suffer interfacial debonding from geopolymer drying shrinkage, requiring surface functionalization | Contact angle goniometry, AFM roughness, and shrinkage strain monitoring | Section 3.2 & 3.5, Fig. 5 & 9 | verified_from_pdf |
Verification status
- PDF preserved: yes (
ranjbar-2016-fiber-reinforced-geopolymer-composites.pdf) - Text extracted: yes (
full_text/ranjbar-2016-fiber-reinforced-geopolymer-composites_full_text.md) - DOI verified: yes (
10.1016/j.compscitech.2015.11.009) - Metadata verified: yes (Compos. Sci. Technol., Vol. 122, pp. 73–81, 2016)
- Claim-evidence matrix ready: yes
Cautions
- Untreated PP fibers in geopolymer pastes have weak physical adhesion; chemical plasma treatment or hydrophilic coating is required to achieve PSH multiple cracking.
- Micro steel fiber dosages above 3.0 vol. % cause severe fresh mixture stiffening and high density ($\rho > 2.4\text{ g/cm}^3$).