Kumar et al. (2022) — Effect of Sand Content on Bond Performance of Engineered Geopolymer Composites (EGC) Repair Material

Citation

Kumar, S., Das, C. S., Lao, J., Alrefaei, Y., & Dai, J.-G. (2022). Effect of sand content on bond performance of engineered geopolymer composites (EGC) repair material. Construction and Building Materials, 328, 127080.

• DOI: 10.1016/j.conbuildmat.2022.127080
• Atlas layer: core
• Related Victor Li book chapter: Chapter 4: Matrix Flaw Size and Sand Tailoring & Chapter 11: Concrete Repair and Structural Retrofitting (pp. 307–335)
• Source PDF: kumar-2022-effect-of-sand-content-on-bond.pdf
• Extracted text: full_text/kumar-2022-effect-of-sand-content-on-bond_full_text.md
• Source note: source_notes/kumar-2022-effect-of-sand-content-on-bond_source_note.md

Why this paper matters

Systematically demonstrates that increasing the sand-to-binder ($S/B$) ratio from 0.3 to 1.0 in ambient-cured PE-EGC suppresses interface shrinkage microcracking, elevates composite elastic modulus (up to 22.8 GPa), and boosts substrate concrete bond strength above the 1.5 MPa BS EN structural threshold while retaining $> 3.5\%$ direct tensile ductility.

Main contribution

• Investigates the parametric effect of sand-to-binder ($S/B = 0.3, 0.45, 0.6, 0.8, 1.0$) on the mechanical, physical, and bond properties of ambient-cured FA/GGBFS PE-EGC ($V_f = 1.50\text{ vol. \%}$).
• Evaluates substrate concrete bond performance using direct pull-off tests, slant shear tests, and steel rebar pullout bond tests.
• Proves that higher sand content mitigates high geopolymer paste shrinkage, eliminating interfacial shear micro-defects and increasing concrete bond strength directly with composite elastic modulus.
• Shows that $S/B \ge 0.8$ satisfies the BS EN 1504-3 structural repair requirement ($f_{bond} \ge 1.5\text{ MPa}$), while achieving 28-day tensile strain capacities of 3.5 % to 7.8 %.
• Achieves significant economic and sustainability benefits by reducing binder and chemical activator content per cubic meter.

Evidence summary

• Material Matrix: Class F Fly Ash + GGBFS (50:50) activated with liquid $\text{NaOH} + \text{Na}2\text{SiO}_3$ ($M_s = 1.2$), micro-silica sand ($D1.0$), $w/b = 0.36$.} = 300\ \mu\text{m}$, $S/B = 0.3\text{--
• Fiber Specifications: 1.50 vol. % UHMWPE fibers ($l_f = 12\text{ mm}, d_f = 24\ \mu\text{m}, \sigma_f = 3000\text{ MPa}, E_f = 100\text{ GPa}$).
• Mechanical & Bond Properties (28 days):
• Compressive strength: 42.5 to 56.4 MPa.
• Elastic modulus ($E_c$): Increased from 14.5 GPa ($S/B = 0.3$) to 22.8 GPa ($S/B = 1.0$).
• Direct tensile ductility ($\epsilon_u$): 7.8 % at $S/B = 0.3$; 5.4 % at $S/B = 0.6$; 3.5 % at $S/B = 1.0$.
• Tensile strength ($\sigma_u$): 4.5 to 8.2 MPa.
• Substrate pull-off bond strength: Increased from 0.85 MPa ($S/B = 0.3$) to 1.72 MPa ($S/B = 1.0$), exceeding the 1.5 MPa code limit.
• Steel rebar pullout bond strength: Peaked at 18.5 MPa for $S/B = 0.6$.

Linked Atlas nodes

• 02_concepts/strain_hardening_criteria.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
• 05_experiments/slant_shear_test.md
• 02_concepts/circular_economy_materials.md

Relationship to Victor Li book

• Extends Victor Li (2019) Chapter 4 (Matrix Flaw Size and Sand Content, pp. 77–114) and Chapter 11 (Concrete Repair, pp. 307–335).
• Resolves the structural overlay paradox: while high sand content slightly reduces ultimate tensile ductility (from 7.8 % to 3.5 %), it significantly restrains paste shrinkage and stiffens the overlay, preventing edge delamination and maximizing interface adhesion to existing concrete structures.

Claim-evidence rows to add

Verification status

• PDF preserved: yes (kumar-2022-effect-of-sand-content-on-bond.pdf)
• Text extracted: yes (full_text/kumar-2022-effect-of-sand-content-on-bond_full_text.md)
• DOI verified: yes (10.1016/j.conbuildmat.2022.127080)
• Metadata verified: yes (CBM, Vol. 328, 127080, 2022)
• Claim-evidence matrix ready: yes

Cautions

• At $S/B = 1.0$, tensile strain capacity drops to 3.5 % due to larger aggregate-induced flaw sizes and higher matrix toughness; however, multiple cracking remains saturated.
• Rebar bond strength plateaus above $S/B = 0.6$; further sand increases do not enhance steel-matrix interlock.