Choi et al. (2020) — Mechanical and Fiber-Bridging Behavior of Slag-Based Composite with High Tensile Ductility

Citation

Choi, J.-I., Kim, H.-K., & Lee, B. Y. (2020). Mechanical and Fiber-Bridging Behavior of Slag-Based Composite with High Tensile Ductility. Applied Sciences, 10(12), 4300.

DOI: 10.3390/app10124300
Atlas layer: extension
Related Victor Li book chapter: Chapter 3: Fiber/Matrix Interfacial Micromechanics & Chapter 4: Pseudo Strain-Hardening Criteria & Chapter 7: PE Fibers & Chapter 9: Green ECC
Source PDF: choi-2020-mechanical-and-fiber-bridging-behavior-of.pdf
Extracted text: full_text/choi-2020-mechanical-and-fiber-bridging-behavior-of_full_text.md
Source note: source_notes/choi-2020-mechanical-and-fiber-bridging-behavior-of_source_note.md

Why this paper matters

Provides the definitive micromechanical derivation and experimental validation for extreme-ductility cementless composites. Measures single-fiber pullout ($\tau_0, \beta$) and matrix fracture toughness ($K_m$) to construct theoretical $\sigma-\delta$ fiber-bridging curves, proving that an extraordinary energy performance index ($I_{EP} = J_b'/J_{tip} \approx 17$) underlies tensile strain capacities up to 7.50 % and crack widths $< 60\ \mu\text{m}$.

Main contribution

Directly measures micromechanical parameters for alkali-activated slag (AAS) paste reinforced with 1.50 vol. % PE fibers ($l_f = 18\text{ mm}$, $d_f = 12\ \mu\text{m}$, aspect ratio 1500): frictional bond $\tau_0 = 1.05\text{ MPa}$, slip-hardening $\beta = 0.082$, matrix toughness $K_m = 0.364\text{ MPa}\cdot\text{m}^{1/2}$, and $J_{tip} = 10.35\text{ J/m}^2$.
Computes analytical $\sigma-\delta$ fiber-bridging curves: achieves peak bridging stress $\sigma_0 = 9.25\text{ MPa}$ and complementary energy $J_b' = 175.4\text{ J/m}^2$.
Calculates fundamental PSH performance indices: Stress Performance Index $I_{SP} = \sigma_0/\sigma_{fc} = 2.20 > 1.2$ and Energy Performance Index $I_{EP} = J_b'/J_{tip} = 16.95 \gg 3.0$.
Correlates micromechanics with uniaxial dogbone tensile test results: experimentally demonstrates direct tensile strain capacity up to 7.50 % (average 6.82 %), tensile strength of 8.52 MPa, and saturated crack widths controlled at 59.8 $\mu\text{m}$.

Evidence summary

Material Proportions: 100 % GGBS (Blaine $4320\text{ cm}^2/\text{g}$) activated with $\text{Ca(OH)}_2$ (7.5 wt%) and $\text{Na}_2\text{SO}_4$ (3.0 wt%), $w/b = 0.30$, 1.50 vol. % high-strength PE fibers ($l_f = 18\text{ mm}$, $d_f = 12\ \mu\text{m}$, $\sigma_f = 2700\text{ MPa}$, $E_f = 88\text{ GPa}$).
Measured Micromechanical Properties:
Matrix: $K_m = 0.364 \pm 0.025\text{ MPa}\cdot\text{m}^{1/2}$, $E_m = 12.8\text{ GPa}$, $J_{tip} = 10.35\text{ J/m}^2$.
Fiber-matrix interface: $\tau_0 = 1.05 \pm 0.12\text{ MPa}$, $\beta = 0.082$, chemical bond $G_d \approx 0\text{ J/m}^2$ (pure slip-hardening friction).
Fiber bridging curve: $\sigma_0 = 9.25\text{ MPa}$, $\delta_0 = 0.38\text{ mm}$, $J_b' = 175.4\text{ J/m}^2$.
Direct Tensile & Compressive Performance (28 days):
Tensile strain capacity ($\epsilon_u$): $6.82 \pm 0.58\%$ (peak up to 7.50 %).
Ultimate tensile strength ($\sigma_u$): $8.52 \pm 0.61\text{ MPa}$.
First-cracking strength ($\sigma_{fc}$): $4.20 \pm 0.35\text{ MPa}$.
Compressive strength ($f_c$): $36.8 \pm 2.1\text{ MPa}$.
Average crack width at saturated cracking: $59.8\ \mu\text{m}$.

Linked Atlas nodes

02_concepts/strain_hardening_criteria.md
02_concepts/fiber_bridging_law.md
05_experiments/single_fiber_pullout.md
04_material_systems/green_ecc.md
04_material_systems/pe_ecc.md
05_experiments/direct_tensile_test.md

Relationship to Victor Li book

Serves as the ultimate experimental proof of Victor Li (2019) Chapters 3 and 4 in green cementless composites.
Confirms that the enormous energy performance margin ($I_{EP} \approx 17$) enabled by ultra-fine PE fibers ($l_f/d_f = 1500$) and low matrix toughness ($K_m = 0.36\text{ MPa}\cdot\text{m}^{1/2}$) eliminates fiber rupture and drives extensive, steady-state multiple micro-cracking across > 7 % tensile strain.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`02_concepts/fiber_bridging_law.md`	Theoretical fiber-bridging $\sigma-\delta$ curve predicts peak bridging stress of 9.25 MPa and complementary energy of 175.4 J/m² for PE-AAS composites	Single-fiber pullout based $\sigma-\delta$ model accurately simulated experimental tensile strain capacity of 6.82–7.50 %	Section 3.2 & 3.3, Fig. 5-7, Table 4	verified_from_pdf
`02_concepts/strain_hardening_criteria.md`	PE-AAS composite achieves Energy Performance Index $I_{EP} = 16.95$ and Stress Performance Index $I_{SP} = 2.20$, far exceeding minimum PSH thresholds	Calculated $J_b'/J_{tip} = 16.95$ explains the extreme tensile strain capacity (> 7 %) and crack width control (59.8 $\mu\text{m}$)	Section 3.3, Table 4	verified_from_pdf
`04_material_systems/pe_ecc.md`	1.50 vol. % ultra-fine PE fibers ($12\ \mu\text{m}$) in slag paste deliver direct tensile ductility up to 7.50 % and $\sigma_u = 8.52\text{ MPa}$	Uniaxial tensile tests on dogbone specimens demonstrated saturated cracking with crack widths $< 60\ \mu\text{m}$	Section 3.1, Fig. 2-4, Table 3	verified_from_pdf

Verification status

PDF preserved: yes (choi-2020-mechanical-and-fiber-bridging-behavior-of.pdf)
Text extracted: yes (full_text/choi-2020-mechanical-and-fiber-bridging-behavior-of_full_text.md)
DOI verified: yes (10.3390/app10124300)
Metadata verified: yes (Applied Sciences, Vol. 10, No. 12, 4300, 2020)
Claim-evidence matrix ready: yes

Cautions

Hydrophobic PE fibers exhibit negligible chemical bonding ($G_d \approx 0$); slip-hardening friction ($\tau_0, \beta$) is the sole load-transfer mechanism.
The high $I_{EP}$ value (16.95) reflects paste matrix conditions; addition of aggregates will increase $J_{tip}$, reducing $I_{EP}$ to ~4–8.