Alemu et al. (2025) — Chloride Diffusion Threshold and Electrochemical Corrosion in Self-Healing ECC

Citation

Abel Shiferaw Alemu, Gebremicael Liyew, Bang Yeon Lee, Hyeong-Ki Kim (2025). Effect of self-healing of cracks in chloride ion diffusion and corrosion of engineered cementitious composites. Journal of Materials Research and Technology, 35, 1054–1071.

• DOI: 10.1016/j.jmrt.2025.01.037
• Atlas layer: supporting
• Related Victor Li book chapter: Chapter 8: Self-Healing and Durability & Chapter 10: Durability Design
• Source PDF: primary_data/alemu-2025-effect-of-self-healing-of-cracks.pdfIJP08225E_Effect of self-healing of cracks chloride_JMRT.pdf`
• Extracted text: secondary_data/full_texts/alemu-2025-effect-of-self-healing-of-cracks_full_text.mdsecondary_data/full_texts/IJP08225E_Effect of self-healing of cracks chloride_JMRT_full_text.md`
• Source note: secondary_data/source_notes/alemu-2025-effect-of-self-healing-of-cracks_source_note.mdsecondary_data/source_notes/IJP08225E_Effect of self-healing of cracks chloride_JMRT_source_note.md`

Why this paper matters

Provides critical fundamental insight into the boundary between water-tightness and chloride ion impermeability in self-healing ECC (slag-cement hybrid with PE/PVA fibers and SAP). Proves that a 100 % healed fraction in water permeability tests does NOT prevent chloride penetration unless crack widths are kept below $0.15\text{ mm}$ ($150\ \mu\text{m}$). Demonstrates via 91-day electrochemical tracking (OCP, LPR, EIS) that while chloride ingress depassivates embedded rebar within 1–3 days ($E_{corr} = -400\text{--}-550\text{ mV}$), autogenous self-healing chokes oxygen and ion diffusion to suppress corrosion currents from peak levels ($5.9\text{--}9.0\ \mu\text{A/cm}^2$) back to uncracked baseline levels ($2.3\ \mu\text{A/cm}^2$) within 1–2 months.

Main contribution

• Water-Tightness vs Chloride Impermeability Threshold: Established that water-tightness (healed fraction = 1.0) is not sufficient to prevent chloride penetration; effective chloride diffusion resistance strictly requires crack widths below $0.15\text{ mm}$.
• Self-Healing Corrosion Propagation Mitigation: Direct immersion in 3.5 wt% NaCl caused rebar depassivation within 1–3 days (5x spike in $i_{corr}$), but autogenous healing products choked mass transport, returning corrosion current to pre-crack baseline levels ($2.3\ \mu\text{A/cm}^2$) within 4–9 weeks.
• EIS Monitoring of Interfacial Healing: EIS bulk resistance ($R_b$) captured a 70–95 % drop upon cracking and subsequent 30–120 % recovery during 91 days of self-healing, validating EIS as a non-destructive monitoring technique for crack self-healing.

Evidence summary

• Chloride Penetration vs Crack Width (28d water self-healing + 35d NaCl exposure):
• Healed fraction in permeability test: 0.95–1.00 for all M1 and M2 specimens (Table 3, Page 6).
• Uncracked penetration depth: $3.5\text{ mm}$ (M1) and $3.2\text{ mm}$ (M2) (Page 7).
• Cracked self-healed specimens:
  • $w_c < \mathbf{0.15\text{ mm}}$: Shallow penetration ($4.3\text{--}15.5\text{ mm}$) (Table 4 & Fig. 8, Pages 6–7).
  • $w_c > \mathbf{0.15\text{ mm}}$: Deep to full penetration ($25.7\text{--}50.0\text{ mm}$), despite complete water-tightness.
  • Unhealed control: Full 50 mm penetration.
• Electrochemical Corrosion Monitoring (91 Days):
• Depassivation phase (Days 1–3): $E_{corr}$ dropped to $-400\text{--}-550\text{ mV}$, $i_{corr}$ spiked from $2.3\ \mu\text{A/cm}^2$ to $5.9\ \mu\text{A/cm}^2$ (M1) and $9.0\ \mu\text{A/cm}^2$ (M2), $R_b$ dropped by 70–95 % (Figs. 10–13, Pages 8–11).
• Healing suppression phase (Weeks 4–9): $i_{corr}$ decayed back to pre-crack baseline ($2.3\ \mu\text{A/cm}^2$), and $R_b$ recovered by 30–120 % (Figs. 14–15, Pages 12–13).

Linked Atlas nodes

• 04_material_systems/self_healing_ecc.md
• 02_concepts/transport_properties.md
• 05_experiments/crack_width_distribution.md
• 04_material_systems/green_ecc.md

Relationship to Victor Li book

• Primary book anchor remains Victor Li (2019), Engineered Cementitious Composites (ECC).
• Directly supports and refines Chapter 8 (Self-Healing) and Chapter 10 (Durability Design) by demonstrating that water-tightness does not equal chloride impermeability, establishing the $0.15\text{ mm}$ crack width limit for chloride diffusion resistance, and proving via in-situ OCP/LPR/EIS that self-healing suppresses steel corrosion propagation rates ($i_{corr} \rightarrow 2.3\ \mu\text{A/cm}^2$) even after depassivation has occurred.

Claim-evidence rows to add

Verification status

• PDF preserved: yes (in primary_data/IJP08225E_Effect of self-healing of cracks chloride_JMRT.pdf)
• Text extracted: yes (PyMuPDF, 18 pages)
• DOI verified: yes (10.1016/j.jmrt.2025.01.037)
• Page/figure/table verified: yes (all checked in PDF text)
• Claim-evidence matrix ready: yes

Cautions

• Rebar passive film does not regenerate in 3.5 wt% NaCl solution; corrosion suppression is governed by diffusion resistance.
• Cracks above $0.15\text{ mm}$ allow deep chloride ingress despite reaching 100 % water-tightness in permeability tests.