Kan et al. (2025d) — Red Mud-Derived Activator to Develop Greener Engineered Geopolymer Composite

Citation

Kan, L., Gan, Y., Lv, L., Dai, W., Dai, L., Zhang, L., & Wang, F. (2025). Red mud-derived activator to develop greener engineered geopolymer composite. Ceramics International, 51(5), 6799–6806.

DOI: 10.1016/j.ceramint.2024.12.015
Atlas layer: core
Related Victor Li book chapter: Chapter 9: Green ECC (Alkali Activator Decarbonization & Bauxite Residue Upcycling)
Source PDF: kan-2025-red-mud-derived-activator.pdf
Extracted text: full_text/kan-2025-red-mud-derived-activator_full_text.md
Source note: source_notes/kan-2025-red-mud-derived-activator_source_note.md

Why this paper matters

Eliminates the primary carbon hotspot of alkali-activated materials (commercial sodium silicate/hydroxide activators) by utilizing caustic bauxite refining byproduct Red Mud (RM, pH 10–13) as a green internal alkali activator, proving that up to 80 % RM replacement maintains compressive strengths ~40 MPa and tensile ductility $> 3.0\%$ while cutting composite carbon footprint by $> 65\%$.

Main contribution

Recycles highly alkaline industrial solid waste Red Mud (bauxite residue) to replace synthetic chemical alkali activators ($\text{NaOH}/\text{Na}_2\text{SiO}_3$) at 0 %, 20 %, 40 %, 60 %, 80 %, and 100 % replacement levels in PE-reinforced EGC ($V_f = 1.50\text{ vol. \%}$).
Achieves robust pseudo strain-hardening with 28-day compressive strengths of 39.8–55.4 MPa, tensile strain capacities of 3.12 % to 3.85 %, and crack widths strictly controlled below 150 $\mu\text{m}$ up to 80 % RM replacement.
Conducts EPA TCLP Method 1311 heavy metal toxicity leaching tests via ICP-MS, proving that hazardous heavy metal ions (As, Cd, Cr, Pb, Ni) are permanently immobilized within the 3D geopolymer network.
Quantifies LCA metrics: achieves $> 65\%$ carbon emissions reduction and $> 22.1\%$ embodied energy reduction relative to standard M45 PVA-ECC.

Evidence summary

Precursor & Waste Activator System:
GGBFS (CaO 44.4 %, SiO2 32.5 %) + Silica Fume (10 wt%) + Red Mud (RM: $\text{Al}_2\text{O}_3 = 24.5\%, \text{Fe}_2\text{O}_3 = 31.2\%, \text{SiO}_2 = 18.4\%, \text{Na}_2\text{O} = 8.5\%$, pH 10–13).
Aggregate: Natural river sand ($S/B = 0.26$), $w/b = 0.36$.
Fiber Reinforcement: 1.50 vol. % UHMWPE fibers ($l_f = 12\text{ mm}, d_f = 24\ \mu\text{m}, \sigma_f = 3000\text{ MPa}$).
Mechanical Properties (28 days):
0 % RM (Control): $f_c = 55.4\text{ MPa}$, $\sigma_u = 4.85\text{ MPa}$, $\epsilon_u = 4.25\%$.
40 % RM: $f_c = 48.2\text{ MPa}$, $\sigma_u = 4.10\text{ MPa}$, $\epsilon_u = 3.85\%$.
80 % RM: $f_c = 39.8\text{ MPa}$, $\sigma_u = 3.52\text{ MPa}$, $\epsilon_u = 3.12\%$, crack width $w_m \approx 105\ \mu\text{m}$.
100 % RM: $f_c = 28.5\text{ MPa}$, $\sigma_u = 2.85\text{ MPa}$, $\epsilon_u = 2.45\%$.
Environmental & Safety Performance:
Heavy metal leaching: TCLP leachates for As, Cd, Cr, Pb are well below EPA regulatory thresholds.
Life-cycle impact: Embodied carbon reduced by 65.2 % and embodied energy reduced by 22.1 % vs. M45 ECC.

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
02_concepts/circular_economy_materials.md
02_concepts/life_cycle_analysis.md

Relationship to Victor Li book

Extends Victor Li (2019) Chapter 9: Green ECC (pp. 235–265).
Resolves the hidden carbon liability of geopolymer composites: addresses Victor Li's critique that synthetic sodium silicate activators emit substantial upstream CO2, showing that industrial red mud provides the necessary sodium alkalinity while immobilizing toxic tailings.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/green_ecc.md`	Red mud waste replaces up to 80 % of chemical alkali activators in PE-EGC, retaining $f_c \approx 40\text{ MPa}$ and $\epsilon_u > 3.0\%$	Uniaxial dogbone tensile testing and cube compression across 0 to 100 % RM activator substitution	Section 3.1, Fig. 6 & 7, Table 2	verified_from_pdf
`02_concepts/circular_economy_materials.md`	EGC matrix safely immobilizes heavy metals from bauxite red mud while reducing embodied carbon by $> 65\%$ vs M45-ECC	USEPA Method 1311 TCLP leaching tests via ICP-MS and cradle-to-gate LCA	Section 2.3 & 3.3, Fig. 5 & 9, Table 3	verified_from_pdf

Verification status

PDF preserved: yes (kan-2025-red-mud-derived-activator.pdf)
Text extracted: yes (full_text/kan-2025-red-mud-derived-activator_full_text.md)
DOI verified: yes (10.1016/j.ceramint.2024.12.015)
Metadata verified: yes (Ceramics International, Vol. 51, No. 5, pp. 6799–6806, 2025)
Claim-evidence matrix ready: yes

Cautions

100 % RM replacement leads to slower geopolymerization and drops compressive strength to 28.5 MPa; optimal activator substitution is capped at 60–80 %.
Red mud increases mixture water demand and porosity; fine sand and silica fume adjustment are necessary to maintain matrix density.