Lao et al. (2023b) — Seawater Sea-Sand Engineered Geopolymer Composites (EGC) with High Strength and High Ductility

Citation

Lao, J.-C., Huang, B.-T., Xu, L.-Y., Khan, M., Fang, Y., & Dai, J.-G. (2023). Seawater sea-sand Engineered Geopolymer Composites (EGC) with high strength and high ductility. Cement and Concrete Composites, 138, 104998.

DOI: 10.1016/j.cemconcomp.2023.104998
Atlas layer: core
Related Victor Li book chapter: Chapter 4: Pseudo Strain-Hardening Criteria & Chapter 9: Green ECC (Seawater Sea-Sand Systems) & Chapter 10: Long-Term Marine Durability
Source PDF: lao-2023-seawater-sea-sand.pdf
Extracted text: full_text/lao-2023-seawater-sea-sand_full_text.md
Source note: source_notes/lao-2023-seawater-sea-sand_source_note.md

Why this paper matters

The definitive Cement and Concrete Composites publication establishing high-strength, high-ductility Seawater Sea-Sand EGC (SS-EGC), achieving compressive strengths $> 140\text{ MPa}$ and direct tensile ductility ~8.0 % with unwashed sea-sand, raw seawater, and 18 mm PE fibers, while cutting embodied carbon by $> 60\%$ vs. cementitious UHS-ECC.

Main contribution

Develops ambient-cured Seawater Sea-Sand EGC (SS-EGC) across FA-dominated (FA/Slag = 8:2) and Slag-dominated (FA/Slag = 2:8) matrices utilizing unwashed marine sea-sand ($D_{max} = 1.18\text{ mm}$), artificial seawater (36 g/L salinity), and 18 mm PE fibers ($V_f = 2.0\text{ vol. \%}$).
Achieves 28-day compressive strengths of 68.4 to 142.5 MPa, ultimate tensile strengths of 7.4 to 13.2 MPa, and direct tensile strain capacities of 7.85 % to 8.42 %.
Employs Digital Image Correlation (DIC), statistical nanoindentation, and isothermal calorimetry to quantify the physical-chemical influence of seawater on reaction kinetics and micro-mechanical properties.
Discovers that seawater magnesium and chloride ions promote the formation of hydrotalcite ($\text{Mg}6\text{Al}_2\text{CO}_3(\text{OH})$) and Friedel's salt phases, increasing matrix nanoindentation modulus and fiber-matrix frictional bond strength.}\cdot 4\text{H}_2\text{O
Proves that SS-EGC possesses superior cracking resistance and substantially lower carbon footprints compared to conventional cement-based SS-ECC.

Evidence summary

Material Proportions:
Precursors: Class F Fly Ash + GGBFS (8:2 and 2:8) + 10 wt% Silica Fume.
Activator: Solid anhydrous $\text{Na}_2\text{SiO}_3$ + liquid waterglass ($M_s = 1.20\text{--}1.50$), borax retarder.
Marine materials: Unwashed sea-sand ($D_{max} = 1.18\text{ mm}, S/B = 0.36$), artificial seawater ($w/b = 0.22\text{--}0.25$).
Fiber Specifications: 2.0 vol. % UHMWPE fibers ($l_f = 18\text{ mm}, d_f = 24\ \mu\text{m}, \sigma_f = 3000\text{ MPa}, E_f = 100\text{ GPa}$).
Mechanical Properties (28 days):
Slag-dominated SS-EGC: Compressive strength $f_c = 142.5 \pm 4.2\text{ MPa}$, Tensile strength $\sigma_u = 13.2 \pm 0.8\text{ MPa}$, Tensile strain capacity $\epsilon_u = 7.85 \pm 0.62\%$.
FA-dominated SS-EGC: Compressive strength $f_c = 68.4 \pm 3.1\text{ MPa}$, Tensile strength $\sigma_u = 7.4 \pm 0.5\text{ MPa}$, Tensile strain capacity $\epsilon_u = 8.42 \pm 0.75\%$.
DIC strain mapping: Saturated multi-cracking with average crack width $w_m < 60\ \mu\text{m}$.
Nanomechanical & Phase Evolution:
Seawater increased mean matrix nanoindentation modulus from 18.5 GPa to 21.2 GPa.
TGA/XRD confirmed higher bound water and hydrotalcite phase formation in seawater mixes.

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/pe_ecc.md
04_material_systems/seawater_sea_sand_ecc.md
05_experiments/direct_tensile_test.md
02_concepts/life_cycle_analysis.md

Relationship to Victor Li book

Extends Victor Li (2019) Chapter 4: PSH Criteria, Chapter 9: Green ECC, and Chapter 10: Marine Durability.
Provides comprehensive experimental proof that replacing fresh water, river sand, and Portland cement with raw seawater, sea-sand, and geopolymer binders preserves the fundamental micromechanical fiber bridging conditions required for high tensile ductility ($\epsilon_u \approx 8\%$) and extreme compressive strength ($f_c > 140\text{ MPa}$).

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/seawater_sea_sand_ecc.md`	SS-EGC achieves compressive strength $> 140\text{ MPa}$ and direct tensile ductility ~8.0 % using unwashed sea-sand and raw seawater	JSCE direct uniaxial tensile testing (DIC-verified) and ASTM compression tests	Section 3.1 & 3.2, Fig. 4-8, Table 3	verified_from_pdf
`02_concepts/strain_hardening_criteria.md`	Marine salts in seawater induce hydrotalcite formation and increase matrix nanoindentation modulus and fiber frictional bond	Statistical nanoindentation, TGA, XRD, and single-fiber pullout test correlation	Section 3.3 & 3.4, Fig. 9-14, Table 4	verified_from_pdf

Verification status

PDF preserved: yes (lao-2023-seawater-sea-sand.pdf)
Text extracted: yes (full_text/lao-2023-seawater-sea-sand_full_text.md)
DOI verified: yes (10.1016/j.cemconcomp.2023.104998)
Metadata verified: yes (Cement and Concrete Composites, Vol. 138, 104998, 2023)
Claim-evidence matrix ready: yes

Cautions

Must be paired with non-corrosive reinforcement (FRP rebar, stainless steel) due to internal chloride content.
Slag-rich mixes require borax retarders to maintain workability for casting.