Humur & Çevik (2022) — Mechanical Characterization of Lightweight Engineered Geopolymer Composites Exposed to Elevated Temperatures

Citation

Humur, G., & Çevik, A. (2022). Mechanical characterization of lightweight engineered geopolymer composites exposed to elevated temperatures. Ceramics International, 48(9), 13634–13650.

DOI: 10.1016/j.ceramint.2022.01.243
Atlas layer: extension
Related Victor Li book chapter: Chapter 8: Lightweight ECC & High-Temperature Behavior & Chapter 9: Green ECC (Fly Ash/Slag Geopolymers)
Source PDF: humur-2022-mechanical-characterization-of-lightweight.pdf
Extracted text: full_text/humur-2022-mechanical-characterization-of-lightweight_full_text.md
Source note: source_notes/humur-2022-mechanical-characterization-of-lightweight_source_note.md

Why this paper matters

Investigates Lightweight Engineered Geopolymer Composites (LEGC) incorporating expanded glass granules and 2.0 vol. % PVA fibers exposed to elevated temperatures up to 800 °C, demonstrating that LEGC achieves densities $< 1880\text{ kg/m}^3$, tensile strain capacities up to 3.33 % at ambient temperature, and retains multiple cracking ductility up to 300 °C while preventing explosive spalling up to 800 °C.

Main contribution

Formulates Lightweight Engineered Geopolymer Composites (LEGC) using fly ash, slag, and 50:50 FA/slag precursors combined with hollow expanded glass granules (EGG) and 2.0 vol. % PVA fibers.
Benchmarks ambient performance against Lightweight Cementitious Composites (LECC): dry density ranges from 1703 to 1883 kg/m³, compressive strength spans 16.7 to 64.1 MPa, and direct tensile strain capacity reaches 2.40 % to 3.33 %.
Exposes specimens to 200 °C, 300 °C, 400 °C, 600 °C, and 800 °C, tracking residual compressive, tensile, flexural, and microstructural changes.
Discovers that strain-hardening and deflection-hardening are preserved up to 300 °C; beyond 300 °C, PVA fiber vaporization creates interconnected micro-channels that release internal pore steam pressure, completely preventing explosive spalling up to 800 °C.

Evidence summary

Precursors & Activator: Class F Fly Ash, GGBFS Slag, and 50:50 FA/Slag blend activated with liquid $\text{NaOH} + \text{Na}_2\text{SiO}_3$.
Lightweight Aggregate: Expanded Glass Granules (EGG, bulk density $300\text{ kg/m}^3$, $D_{max} = 2.0\text{ mm}$).
Fiber Specifications: 2.0 vol. % PVA fibers ($l_f = 12\text{ mm}$, $d_f = 39\ \mu\text{m}$, $\sigma_f = 1600\text{ MPa}$, $E_f = 42\text{ GPa}$).
Ambient Mechanical Performance (20 °C):
Dry density: 1703 to 1883 kg/m³.
Compressive strength ($f_c$): 16.66 to 64.11 MPa (50:50 FA/Slag achieved 48.5 MPa).
Uniaxial tensile strain capacity ($\epsilon_u$): $2.40\%\text{ to }3.33\%$.
Tensile bridging strength: 2.66 to 4.97 MPa.
Residual Performance after Thermal Exposure:
Up to 300 °C: Retains pseudo strain-hardening with multiple micro-cracking.
400–800 °C: PVA fibers melt ($T_m \approx 230\ ^\circ\text{C}$), transitioning to softening behavior; however, geopolymer matrix sintering provides residual compressive strength (15–35 MPa) without spalling.

Linked Atlas nodes

02_concepts/strain_hardening_criteria.md
04_material_systems/geopolymer_ecc.md
04_material_systems/green_ecc.md
04_material_systems/lightweight_ecc.md
04_material_systems/pva_ecc.md
05_experiments/thermal_testing.md

Relationship to Victor Li book

Extends Victor Li (2019) Chapter 8 (Lightweight ECC and Fire Resistance, pp. 205–234) and Chapter 9 (Green ECC).
Validates the sacrificial polymer fiber spalling mitigation mechanism in geopolymer matrices: polymer fiber melting relieves vapor pressure, preventing explosive brittle blowout during fire exposure while the ceramic aluminosilicate matrix undergoes beneficial sintering.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/lightweight_ecc.md`	LEGC utilizing expanded glass granules achieves dry density of 1700–1880 kg/m³ and direct tensile ductility of 2.4–3.3 %	Uniaxial tension and compression testing on lightweight geopolymer composites	Section 3.1 & 3.2, Fig. 5-7, Table 5	verified_from_pdf
`05_experiments/thermal_testing.md`	PVA-LEGC retains pseudo strain-hardening ductility up to 300 °C and avoids explosive spalling up to 800 °C via fiber channel pressure release	Thermal furnace exposure from 200 °C to 800 °C with residual mechanical and SEM microstructural analysis	Section 3.3 & 3.4, Fig. 8-14, Table 6	verified_from_pdf

Verification status

PDF preserved: yes (humur-2022-mechanical-characterization-of-lightweight.pdf)
Text extracted: yes (full_text/humur-2022-mechanical-characterization-of-lightweight_full_text.md)
DOI verified: yes (10.1016/j.ceramint.2022.01.243)
Metadata verified: yes (Ceramics International, Vol. 48, No. 9, pp. 13634–13650, 2022)
Claim-evidence matrix ready: yes

Cautions

Beyond 300 °C, direct tensile ductility is lost due to complete PVA fiber thermal decomposition; structural fire designs must account for reduced post-fire tensile capacity.
Expanded glass granules are crushable under high shear mixing; gentle mixing speeds are required to preserve granule hollow integrity.