Lao et al. (2023) — Strain-Hardening Alkali-Activated Fly Ash/Slag Composites with Ultra-High Compressive Strength and Ultra-High Tensile Ductility

Citation

Lao, J.-C., Huang, B.-T., Fang, Y., Xu, L.-Y., Dai, J.-G., & Shah, S. P. (2023). Strain-hardening alkali-activated fly ash/slag composites with ultra-high compressive strength and ultra-high tensile ductility. Cement and Concrete Research, 165, 107075.

• DOI: 10.1016/j.cemconres.2022.107075
• Atlas layer: core
• Related Victor Li book chapter: Chapter 4: Pseudo Strain-Hardening Criteria (Ultra-High Strength Matrix Design) & Chapter 9: Green ECC (Alkali-Activated Fly Ash/Slag)
• Source PDF: lao-2022-strain-hardening-alkali-activated-fly-ashslag.pdf
• Extracted text: full_text/lao-2022-strain-hardening-alkali-activated-fly-ashslag_full_text.md
• Source note: source_notes/lao-2022-strain-hardening-alkali-activated-fly-ashslag_source_note.md

Why this paper matters

A landmark Cement and Concrete Research study by HK PolyU and Surendra P. Shah establishing a global record for alkali-activated composites: simultaneously achieving ultra-high compressive strength (up to 180.7 MPa) and ultra-high direct tensile ductility (8.1 % to 9.9 %, $\sigma_u$ up to 18.2 MPa) with zero Portland cement clinker.

Main contribution

• Synthesizes Strain-Hardening Alkali-Activated Fly Ash/Slag Composites (SH-AAFSC) using high-reactivity GGBFS, Class F fly ash, and silica fume with 2.0 vol. % PE fibers.
• Pushes the global performance envelope of zero-cement materials, demonstrating compressive strengths of 94.4 to 180.7 MPa and direct tensile strain capacities of 8.1 % to 9.9 % ($\sigma_u = 12.5\text{--}18.2\text{ MPa}$).
• Conducts multi-scale experimental characterization: statistical grid nanoindentation, single-fiber pullout testing, BSE-SEM, MIP, XRD, and 29Si/27Al MAS-NMR.
• Uncovers a strong linear relationship between composite fiber-bridging strength ($\sigma_0$) and the mean matrix indentation modulus ($M_{matrix}$).
• Proves that elevating GGBS content increases the Ca/Si ratio of C-(N)-A-S-H gels, eliminating capillary pores ($< 10\text{ nm}$) to achieve 180+ MPa compressive strength while maintaining slip-hardening fiber pullout without filament rupture.

Evidence summary

• Material Matrix: Class F Fly Ash + GGBFS (FA/GGBS = 8:2, 5:5, 2:8, 0:10) + 10 wt% Silica Fume activated with solid anhydrous $\text{Na}2\text{SiO}_3$ and liquid waterglass ($M_s = 1.10\text{--}1.35$), fine silica sand ($D, S/B = 0.36$), $w/p = 0.22, 0.25, 0.27$.} < 300\ \mu\text{m
• Fiber Specifications: 2.0 vol. % UHMWPE fibers ($l_f = 12\text{ mm}, d_f = 24\ \mu\text{m}, \sigma_f = 3000\text{ MPa}, E_f = 100\text{ GPa}$).
• Mechanical Properties (28 days):
• Compressive strength ($f_c$): 94.4 MPa ($w/p = 0.27$, FA/GGBS 8:2) to 180.7 MPa ($w/p = 0.22$, 100 % GGBS).
• Uniaxial tensile ductility ($\epsilon_u$): $8.1\%\text{ to }9.9\%$ across all mixture series.
• Ultimate tensile strength ($\sigma_u$): 12.5 to 18.2 MPa.
• Saturated crack pattern: Over 80 micro-cracks along the gauge length with average crack width $w_m \approx 30\text{--}55\ \mu\text{m}$.
• Multi-Scale Nanomechanics:
• Grid nanoindentation revealed high-density C-(N)-A-S-H phase fractions with indentation modulus $M = 22\text{--}38\text{ GPa}$.
• Frictional bond strength $\tau_0$ scaled linearly with matrix elastic modulus ($R^2 = 0.94$).

Linked Atlas nodes

• 02_concepts/strain_hardening_criteria.md
• 02_concepts/fiber_bridging_law.md
• 05_experiments/single_fiber_pullout.md
• 04_material_systems/geopolymer_ecc.md
• 04_material_systems/green_ecc.md
• 04_material_systems/pe_ecc.md
• 05_experiments/direct_tensile_test.md
• 02_concepts/interface_properties.md

Relationship to Victor Li book

• Extends Victor Li (2019) Chapter 4: PSH Criteria (pp. 77–114) and Chapter 9: Green ECC (pp. 235–265).
• Completely shatters the classical trade-off between strength and ductility: proves that micromechanical fiber tailoring enables zero-clinker geopolymer systems to match or exceed the highest mechanical performance metrics of cementitious UHPC ($f_c > 180\text{ MPa}$) while providing unmatched tensile strain capacity ($\epsilon_u \approx 10\%$).

Claim-evidence rows to add

Verification status

• PDF preserved: yes (lao-2022-strain-hardening-alkali-activated-fly-ashslag.pdf)
• Text extracted: yes (full_text/lao-2022-strain-hardening-alkali-activated-fly-ashslag_full_text.md)
• DOI verified: yes (10.1016/j.cemconres.2022.107075)
• Metadata verified: yes (Cement and Concrete Research, Vol. 165, 107075, 2023)
• Claim-evidence matrix ready: yes

Cautions

• Formulations with $f_c > 150\text{ MPa}$ ($w/p = 0.22$) require high-shear planetary mixing and polycarboxylate superplasticizers to control severe rheological viscosity.
• Rapid setting occurs in 100 % slag matrices; activator modulus and liquid/solid blending must be tightly controlled.