Kamal et al. (2008) — Crack Opening of SHCC Repair Material

Citation

Kamal, Ahmed, Kunieda, Minoru, Ueda, Naoshi, & Nakamura, Hikaru (2008). Evaluation of crack opening performance of a repair material with strain hardening behavior. Cement and Concrete Composites, 30(10), 863-871.

DOI: 10.1016/j.cemconcomp.2008.08.003
Atlas layer: extension
Related Victor Li book chapter: Chapter 8 (Durability and Infrastructure Applications), Chapter 9 (Repair and Retrofit)
Source PDF: kamal-2008-evaluation-of-crack-opening-performance.pdf
Extracted text: atlas/full_text/kamal-2008-evaluation-of-crack-opening-performance_full_text.md
Source note: atlas/source_notes/kamal-2008-evaluation-of-crack-opening-performance_source_note.md

Why this paper matters

This paper investigates the performance of Ultra-High Performance Strain-Hardening Cementitious Composites (UHP-SHCC, $f_c \approx 95\text{ MPa}$, $\sigma_t \approx 10\text{ MPa}$) as concrete surface repair materials. It reveals that in real repair applications, multiple cracking is restrained and localizes into a narrow zone ($12.8\text{--}20\text{ mm}$) directly over existing substrate cracks. It establishes the Zero-Span Tensile Test as an indispensable design methodology to replace misleading free uniaxial tensile elongation in repair specifications.

Main contribution

UHP-SHCC Formulation & Performance: Developed high-strength, high-ductility SHCC ($W/B = 0.18$, 20% silica fume, $12\ \mu\text{m}\times 6\text{ mm}$ PE fibers) achieving compressive strength $94\text{--}96\text{ MPa}$, tensile strength $3.8\text{--}10\text{ MPa}$, and tensile ductility $0.58\text{--}2.80\%$ ($V_f = 0.5\text{--}1.5\%$).
Zero-Span Tensile Test Methodology: Validated a novel testing method evaluating the localized crack opening capacity of thin repair layers ($10\text{ mm}$) bonded over an artificial crack.
Restrained Cracking Boundary Effects: Demonstrated that free dogbone tensile tests overestimate allowable substrate crack movement by 2.3 to 5.0 times, and proved that zero-span crack opening capacity ($0.124\text{--}0.297\text{ mm}$) matches actual repaired RC beam flexural cracking.

Evidence summary

Material properties (14 days): UHP-SHCC(1.5%) achieved compressive strength $96\text{ MPa}$, tensile strength $10\text{ MPa}$, and tensile strain capacity $2.80\%$ (Page 865, Table 2, Fig. 3).
Zero-span crack opening capacity: $0.124\text{ mm}$ ($V_f=0.5\%$), $0.237\text{ mm}$ ($V_f=1.0\%$), and $0.297\text{ mm}$ ($V_f=1.5\%$) (Page 867, Table 3, Fig. 8).
Cracked zone width in repaired RC beams: Measured at $12.8\text{ mm}$ for $V_f=1.0\%$ and $20\text{ mm}$ for $V_f=1.5\%$, mirroring zero-span cracked width of $16.5\text{ mm}$ and $20\text{ mm}$ (Page 870, Table 4, Figs. 9, 13).
Uniaxial vs zero-span comparison: Tensile deformation capacity in free uniaxial tension was 2.3 to 5.0 times higher than zero-span opening (Pages 870-871, Fig. 15).

Linked Atlas nodes

02_concepts/strain_hardening_criteria.md
05_experiments/direct_tensile_test.md
05_experiments/crack_width_distribution.md

Relationship to Victor Li book

Extends Chapters 8 & 9 by providing critical experimental boundary condition insight for patch repair and overlay engineering.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`05_experiments/direct_tensile_test.md`	Multiple cracking in bonded SHCC repair overlays is constrained to a 12.8-20 mm band over existing substrate cracks.	Flexural testing on repaired pre-cracked RC beams.	Pages 869-870, Table 4, Fig. 13	verified_from_pdf
`05_experiments/direct_tensile_test.md`	Free uniaxial tensile strain capacity overestimates bonded overlay crack opening capacity by 2.3-5.0×.	Comparison of zero-span tensile test and uniaxial tension results.	Pages 870-871, Table 3, Fig. 15	verified_from_pdf
`02_concepts/strain_hardening_criteria.md`	UHP-SHCC with W/B = 0.18 and fine PE fibers achieves compressive strength ~95 MPa and tensile strength 10 MPa with 2.8% strain capacity.	Mechanical property characterization at 14 days.	Page 865, Table 2, Fig. 3	verified_from_pdf

Verification status

PDF preserved: yes (kamal-2008-evaluation-of-crack-opening-performance.pdf)
Text extracted: yes (atlas/full_text/kamal-2008-evaluation-of-crack-opening-performance_full_text.md)
DOI verified: yes (10.1016/j.cemconcomp.2008.08.003)
Page/figure/table verified: yes (Pages 863-871, Tables 1-4, Figs. 1-15 verified from PDF)
Claim-evidence matrix ready: yes

Cautions

Do not use free uniaxial tensile elongation as the allowable crack opening specification in concrete repair; use zero-span crack opening capacity.