Wang et al. (2021) — Effect of CNFs on the mechanical properties and microstructure...

Citation

Siyu Wang, Chenlong Lin, Shan Li, Miao Chen, Yiyan Lu (2021). Effect of CNFs on the mechanical properties and microstructure of early strength seawater sea-sand engineered cementitious composites. Construction and Building Materials, Vol. 307, Article 124961.

DOI: 10.1016/j.conbuildmat.2021.124961
Atlas layer: extension
Related Victor Li book chapter: Chapter 3: Micro-mechanics; Chapter 4: Sustainable/Marine ECC
Source PDF: wang-2021-effect-of-cnfs-on-the.pdf
Extracted text: atlas/full_text/wang-2021-effect-of-cnfs-on-the_full_text.md
Source note: atlas/source_notes/wang-2021-effect-of-cnfs-on-the_source_note.md

Why this paper matters

Pioneers multi-scale nano-reinforcement in marine ECC by incorporating 0.02 wt% carbon nanofibers (CNFs) with 1.6 vol% PVA fibers in rapid-hardening sulfoaluminate seawater sea-sand ECC, successfully doubling tensile ductility from 2.34% to 4.47% and narrowing crack widths to 83.4 μm.

Main contribution

Optimized surfactant-assisted ultrasonic dispersion of CNFs in seawater (CTAB surfactant at 1:2 CNF mass ratio with 30 min sonication).
Demonstrated that CNFs bridge nanoscale cracks and fill capillary pores, increasing 14d compressive strength by 21–24% and tensile strength to 5.02 MPa.
Doubled tensile strain capacity ($2.34\% \rightarrow 4.47\%$ in seawater SS-ECC) with crack density increasing from 14 to 38 and average crack width decreasing by >54%.

Evidence summary

Compressive strength: 14-day compressive strength increased by 21–24% with CTAB-dispersed CNFs (Fig. 13, page 9).
Direct tensile properties:
Control without CNFs (seawater): $\sigma_{tu} = 4.32\text{ MPa}$, $\varepsilon_{tu} = 2.34\%$, crack count = 14, crack width = $182.6\ \mu\text{m}$.
CNF + CTAB (seawater): $\sigma_{tu} = 5.02\text{ MPa}$, $\varepsilon_{tu} = 4.47\%$, crack count = 38, crack width = $83.4\ \mu\text{m}$.
CNF + CTAB (distilled water): $\sigma_{tu} = 4.94\text{ MPa}$, $\varepsilon_{tu} = 4.77\%$, crack count = 55, crack width = $62.3\ \mu\text{m}$ (Table 4, page 10).
Porosity: MIP proved harmful pores ($>100\text{ nm}$) were significantly eliminated.

Linked Atlas nodes

04_material_systems/green_ecc.md
02_concepts/extreme_ductility_ecc.md
02_concepts/strain_hardening_criteria.md
05_experiments/direct_tensile_test.md

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/green_ecc.md`	Adding 0.02 wt% CTAB-dispersed CNFs doubles tensile ductility of rapid-hardening SS-ECC from 2.34% to 4.47% and halves residual crack width.	Direct tensile tests showed strain capacity increased from 2.34% to 4.47% and crack width dropped from 182.6 to 83.4 μm.	Pages 1, 10, Section 3.2.1, Table 4, Fig. 15	verified_from_pdf
`02_concepts/strain_hardening_criteria.md`	CNFs refine pore structure and bridge sub-micron microcracks, increasing tensile multiple cracking density and compressive strength.	MIP porosity and FE-SEM imaging confirmed pore blocking and nano-bridging of cracks by dispersed CNFs.	Pages 10-12, Section 3.2.2 & 3.2.3, Figs. 17-19	verified_from_pdf

Verification status

PDF preserved: yes (wang-2021-effect-of-cnfs-on-the.pdf)
Text extracted: yes (atlas/full_text/wang-2021-effect-of-cnfs-on-the_full_text.md)
DOI verified: yes (10.1016/j.conbuildmat.2021.124961)
Page/figure/table verified: yes
Claim-evidence matrix ready: yes

Cautions

Avoid anionic surfactants (SDS) due to severe foam generation leading to 50% compressive strength loss.