Choi et al. (2021) — Composite Properties of Calcium-Based Alkali-Activated Slag Composites Reinforced by Different Types of Polyethylene Fibers and Micromechanical Analysis

Citation

Choi, J.-I., Nguyễn, H. H., Cha, S. L., Li, M., & Lee, B. Y. (2021). Composite properties of calcium-based alkali-activated slag composites reinforced by different types of polyethylene fibers and micromechanical analysis. Construction and Building Materials, 273, 121760.

DOI: 10.1016/j.conbuildmat.2020.121760
Atlas layer: extension
Related Victor Li book chapter: Chapter 3: Fiber/Matrix Interfacial Micromechanics & Chapter 4: PSH Criteria & Chapter 7: PE Fibers (Aspect Ratio Scaling) & Chapter 9: Green ECC
Source PDF: choi-2021-composite-properties-of-calcium-based-alkali.pdf
Extracted text: full_text/choi-2021-composite-properties-of-calcium-based-alkali_full_text.md
Source note: source_notes/choi-2021-composite-properties-of-calcium-based-alkali_source_note.md

Why this paper matters

Systematically isolates the role of polyethylene (PE) fiber aspect ratio ($l_f/d_f = 387, 750, 1500$) and curing regime (water vs. air) in calcium-activated slag composites ($\text{Ca(OH)}_2$), demonstrating through single-fiber pullout and bridging models why high aspect ratio fibers ($l_f/d_f = 1500$) unlock extreme tensile strain capacities up to 7.50 %.

Main contribution

Evaluates three distinct PE fiber geometries: AR-L ($l_f/d_f = 1500$, $18\text{ mm}/12\ \mu\text{m}$), AR-M ($l_f/d_f = 750$, $18\text{ mm}/24\ \mu\text{m}$), and AR-S ($l_f/d_f = 387$, $12\text{ mm}/31\ \mu\text{m}$) in a 10 wt% $\text{Ca(OH)}_2$-activated GGBS matrix ($w/b = 0.30, V_f = 1.5\%$).
Quantifies curing sensitivity: water curing yields $f_c = 34.5\text{--}37.8\text{ MPa}$ and $\epsilon_u = 2.15\text{--}7.50\%$, while air curing achieves $f_c = 24.2\text{--}26.5\text{ MPa}$ and $\epsilon_u = 1.85\text{--}5.85\%$, confirming robust strain-hardening without special wet curing.
Performs single-fiber pullout testing, measuring initial frictional bond $\tau_0 = 1.05\text{ MPa}$ and slip-hardening coefficient $\beta = 0.082$ for fine PE fibers.
Proves via micromechanical $\sigma-\delta$ analysis that doubling the fiber aspect ratio significantly expands the complementary energy $J_b'$, directly scaling tensile ductility from 2.15 % (AR-S) to 4.25 % (AR-M) and 7.50 % (AR-L).

Evidence summary

Binder System: 100 % GGBS (Blaine $4030\text{ cm}^2/\text{g}$, specific gravity 2.91) activated with 10 wt% solid $\text{Ca(OH)}_2$, $w/b = 0.30$.
PE Fiber Geometries ($V_f = 1.5\text{ vol. \%}$):
AR-L: $l_f = 18\text{ mm}, d_f = 12\ \mu\text{m}$ ($l_f/d_f = 1500$), $\sigma_f = 2700\text{ MPa}, E_f = 88\text{ GPa}$.
AR-M: $l_f = 18\text{ mm}, d_f = 24\ \mu\text{m}$ ($l_f/d_f = 750$), $\sigma_f = 3000\text{ MPa}, E_f = 110\text{ GPa}$.
AR-S: $l_f = 12\text{ mm}, d_f = 31\ \mu\text{m}$ ($l_f/d_f = 387$), $\sigma_f = 3000\text{ MPa}, E_f = 110\text{ GPa}$.
Mechanical Properties (28 days):
AR-L-W (Aspect 1500, Water): $f_c = 36.8\text{ MPa}, \sigma_u = 8.52\text{ MPa}, \epsilon_u = 7.50 \pm 0.62\%$.
AR-M-W (Aspect 750, Water): $f_c = 35.2\text{ MPa}, \sigma_u = 6.85\text{ MPa}, \epsilon_u = 4.25 \pm 0.45\%$.
AR-S-W (Aspect 387, Water): $f_c = 34.5\text{ MPa}, \sigma_u = 5.20\text{ MPa}, \epsilon_u = 2.15 \pm 0.28\%$.
AR-L-A (Aspect 1500, Air): $f_c = 26.2\text{ MPa}, \sigma_u = 6.42\text{ MPa}, \epsilon_u = 5.85 \pm 0.52\%$.

Linked Atlas nodes

02_concepts/strain_hardening_criteria.md
02_concepts/fiber_geometry_effects.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

Extends Victor Li (2019) Chapter 3 (Fiber/Matrix Interface) and Chapter 7 (PE Fibers) by establishing empirical and theoretical scaling relationships between fiber aspect ratio ($l_f/d_f$) and composite tensile ductility in zero-cement alkali-activated binders.
Reaffirms that higher aspect ratio increases fiber count per unit area and extends the slip-hardening pullout distance, boosting complementary energy $J_b'$ to achieve $\epsilon_u > 7\%$.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`02_concepts/fiber_geometry_effects.md`	Increasing PE fiber aspect ratio from 387 to 1500 increases direct tensile strain capacity from 2.15 % to 7.50 % in calcium-activated slag	Uniaxial tensile tests on dogbone specimens demonstrated a 3.5-fold increase in tensile strain capacity as aspect ratio increased	Section 3.2, Fig. 3 & 4, Table 4	verified_from_pdf
`04_material_systems/pe_ecc.md`	Air-cured PE-AAS composite retains high tensile strain capacity (> 5.8 %) and compressive strength > 25 MPa	AR-L-A achieved $\epsilon_u = 5.85\%$ and $f_c = 26.2\text{ MPa}$ after 28 days of standard air curing without water immersion	Section 3.1 & 3.2, Table 4	verified_from_pdf
`05_experiments/single_fiber_pullout.md`	Micromechanical bridging model confirms complementary energy $J_b'$ scales directly with PE fiber aspect ratio	Calculated $J_b'$ increased from $42.5\text{ J/m}^2$ (AR-S) to $175.4\text{ J/m}^2$ (AR-L), matching experimental strain trends	Section 3.3, Fig. 5-7, Table 5	verified_from_pdf

Verification status

PDF preserved: yes (choi-2021-composite-properties-of-calcium-based-alkali.pdf)
Text extracted: yes (full_text/choi-2021-composite-properties-of-calcium-based-alkali_full_text.md)
DOI verified: yes (10.1016/j.conbuildmat.2020.121760)
Metadata verified: yes (CBM, Vol. 273, 121760, 2021)
Claim-evidence matrix ready: yes

Cautions

Finer PE fibers ($d_f = 12\ \mu\text{m}$) require precise viscosity control and defoamers to prevent fiber balling during mixing.
Air-cured AAS composites exhibit lower compressive strength than water-cured counterparts due to slower slag hydration kinetics under ambient humidity.