Alemu et al. (2022) — Self-Healing in CFBC Bottom Ash Modified Slag Cements
Citation
Abel Shiferaw Alemu, Bang Yeon Lee, Solmoi Park, Hyeong-Ki Kim (2022). Self-healing of Portland and slag cement binder systems incorporating circulating fluidized bed combustion bottom ash. Construction and Building Materials, 314, 125571.
- DOI:
10.1016/j.conbuildmat.2021.125571 - Atlas layer: extension
- Related Victor Li book chapter: Chapter 8: Self-Healing and Durability
- Source PDF:
primary_data/alemu-2022-self-healing-of-portland-and-slag.pdfIJP06422E_Self healing CFBC_CBM.pdf` - Extracted text:
secondary_data/full_texts/alemu-2022-self-healing-of-portland-and-slag_full_text.mdsecondary_data/full_texts/IJP06422E_Self healing CFBC_CBM_full_text.md` - Source note:
secondary_data/source_notes/alemu-2022-self-healing-of-portland-and-slag_source_note.mdsecondary_data/source_notes/IJP06422E_Self healing CFBC_CBM_source_note.md`
Why this paper matters
Demonstrates that replacing 10–20 % of Portland and slag cement binders with circulating fluidized bed combustion (CFBC) bottom ash (rich in anhydrite and portlandite) improves water permeability reduction across 0.06–0.11 mm cracks. Formulates the "ideal crack width" ($b$) from Poiseuille-Darcy flow and proves that CFBC ash activates secondary slag hydration in sealed, carbonation-restricted conditions, boosting crack healing from 55 % to 75 %.
Main contribution
- Poiseuille-Darcy Ideal Crack Width Model: Formulated the hydraulic ideal crack width $b = (12 Q \mu / (L \cdot dP/dx))^{1/3}$ with roughness factor $\xi = 0.49$, capturing internal tortuosity and yielding superior correlation with permeability reduction over surface crack widths.
- Carbonation-Free Slag Activation: Proved that 20 % CFBC bottom ash replacement in slag cement (PCS_C20) elevated the 28-day seal-cured healing rate from 55 % to 75 %, reducing reliance on atmospheric $\text{CO}_2$.
- 0.20 mm Healing Boundary: Verified that crack healing occurs exclusively for crack widths under 0.20 mm, with zero permeability reduction observed for 0.30 mm cracks across all binder combinations.
Evidence summary
- Ideal Crack Width vs Flow Correlation: Strong polynomial correlation between ideal crack width ($0.06\text{--}0.11\text{ mm}$) and 28-day flow rate ($R^2$ much higher than surface crack width) (Figs. 6–7, Page 6).
- Self-Healing Permeability Reduction:
- Water-cured:
PCSachieved lowest permeability ($k = 5.5 \times 10^{-11}\text{ m}^2$) and $\approx 89\text{ \%}$ healing rate;PC_C20reached $>85\text{ \%}$ healing rate (Figs. 8–10, Pages 6–7). - Seal-cured:
PCS_C20reached $\approx 75\text{ \%}$ healing rate vs $55\text{ \%}$ for PCS (+20 %p increase). - Mineralogical Verification: SEM and XRD confirmed dense ettringite networks and portlandite-activated slag hydration products in healed crack zones (Figs. 11 & 12, Pages 8–9).
Linked Atlas nodes
04_material_systems/self_healing_ecc.md04_material_systems/green_ecc.md05_experiments/crack_width_distribution.md
Relationship to Victor Li book
- Primary book anchor remains Victor Li (2019), Engineered Cementitious Composites (ECC).
- Directly extends Chapter 8 (Self-Healing ECC) by introducing a fluid-mechanics Poiseuille flow framework for crack hydraulic conductivity and proving that CFBC bottom ash can stimulate autogenous healing via secondary slag hydration even in carbonation-restricted underwater environments.
Claim-evidence rows to add
| Atlas node | Claim | Evidence summary | Page/Figure/Table | Status |
|---|---|---|---|---|
04_material_systems/self_healing_ecc.md |
Flow-based ideal crack width ($b = (12 Q \mu / (L \cdot dP/dx))^{1/3}$) correlates more strongly with self-healing than surface optical crack width | Hydraulic permeability modeling verified superior correlation ($R^2$) for ideal crack width $b$ | Page 125571:1 & 5 / Eq. 4 / Figs. 4, 5, 7 | verified_from_pdf |
04_material_systems/self_healing_ecc.md |
Replacing 20 % slag cement with CFBC bottom ash increases seal-cured (carbonation-free) crack healing rate from 55 % to 75 % | Seal-cured permeability tests recorded 75 % healing for PCS_C20 vs 55 % for PCS | Page 125571:7 & 10 / Figs. 9, 10 | verified_from_pdf |
04_material_systems/self_healing_ecc.md |
Autogenous crack self-healing is strictly inactive for crack widths of 0.30 mm under 28-day water immersion | Zero permeability reduction observed across all binders at 0.30 mm crack width | Page 125571:4 & 9 / Section 3.1 | verified_from_pdf |
Verification status
- PDF preserved: yes (in
primary_data/IJP06422E_Self healing CFBC_CBM.pdf) - Text extracted: yes (PyMuPDF, 10 pages)
- DOI verified: yes (
10.1016/j.conbuildmat.2021.125571) - Page/figure/table verified: yes (all checked in PDF text)
- Claim-evidence matrix ready: yes
Cautions
- CFBC ash must be processed to control sulfur content and avoid excessive delayed expansion.