Negahban et al. (2021) — Pore Gradation Effect on Portland Cement and Geopolymer Concretes

Citation

Negahban, E., Bagheri, A., & Sanjayan, J. (2021). Pore gradation effect on Portland cement and geopolymer concretes. Cement and Concrete Composites, 122, 104141.

DOI: 10.1016/j.cemconcomp.2021.104141
Atlas layer: extension
Related Victor Li book chapter: Chapter 4: Matrix Toughness and Flaw Distribution & Chapter 9: Green ECC (Pore Structure Evolution) & Chapter 10: Transport Properties and Durability
Source PDF: negahban-2021-pore-gradation-portland-geopolymer.pdf
Extracted text: full_text/negahban-2021-pore-gradation-portland-geopolymer_full_text.md
Source note: source_notes/negahban-2021-pore-gradation-portland-geopolymer_source_note.md

Why this paper matters

Provides a multi-scale experimental comparison of pore networks between ambient-cured geopolymer concrete and Portland cement concrete using Liquid Nitrogen Porosimetry (LNP) and image analysis, establishing that geopolymer matrices possess 50–66 % higher nano-scale specific surface area ($25\text{--}60\text{ m}^2/\text{g}$) and a distinct vertical depth-dependent pore gradation.

Main contribution

Characterizes the pore architecture of ambient-cured fly ash/slag/silica fume geopolymer concrete (GPC) versus ordinary Portland cement concrete (OPCC).
Employs a multi-scale analytical suite: Liquid Nitrogen Porosimetry (LNP), Pore Detection Image Analysis (PDIA), Apparent Volume of Permeable Voids (AVPV, ASTM C642), and Ultrasonic Pulse Velocity (UPV).
Discovers that geopolymer gel exhibits a specific surface area of $25\text{--}60\text{ m}^2/\text{g}$, which is 50 % to 66 % higher than OPC ($4.1\text{--}20.8\text{ m}^2/\text{g}$) due to ultra-fine nanometric N-A-S-H/C-A-S-H gel mesopores.
Identifies a vertical pore gradation in cast geopolymer sections, where permeable void volume decreases from top (up to 32 %) to bottom (down to 8 %) with a corresponding shift toward denser nanometric gel pores.
Demonstrates that hybridizing slag and silica fume refines capillary pore connectivity, directly correlating with enhanced compressive strength and durability.

Evidence summary

Material Formulations:
GPC: Class F Fly Ash + GGBFS (up to 30 %) + Silica Fume (up to 10 %) activated with sodium silicate + $\text{NaOH}$ ($M_s = 1.0\text{--}1.5$), ambient-cured ($23\ ^\circ\text{C}$).
OPCC: General Purpose Portland Cement concrete with varying $w/c$ (0.40–0.60).
Pore Network & Microstructural Findings:
Specific Surface Area (LNP): GPC = $25.4\text{--}62.1\text{ m}^2/\text{g}$; OPCC = $4.1\text{--}20.8\text{ m}^2/\text{g}$.
Void volume (PDIA / AVPV): OPCC = 7 % to 14 %; GPC = 8 % to 32 % (strong spatial variation).
Vertical Gradation: Top-layer porosity is 1.5–2.5x higher than bottom-layer porosity in ambient-cured GPC elements due to bleed-water migration and density stratification.
Compressive strength: GPC mixes achieved 35–65 MPa at 28 days, strongly governed by the fraction of pores $< 50\text{ nm}$.

Linked Atlas nodes

02_concepts/strain_hardening_criteria.md
04_material_systems/geopolymer_ecc.md
04_material_systems/green_ecc.md
02_concepts/matrix_fracture_toughness.md
02_concepts/circular_economy_materials.md

Relationship to Victor Li book

Extends Victor Li (2019) Chapter 4 (Matrix Toughness & Flaw Distributions) and Chapter 10 (Durability / Transport Properties).
Explains the micromechanical basis of geopolymer matrix fracture toughness ($K_m$): the high nano-scale surface area and refined gel pores reduce capillary water transport while altering interfacial bond development with reinforcing fibers.

Claim-evidence rows to add

Atlas node	Claim	Evidence summary	Page/Figure/Table	Status
`04_material_systems/geopolymer_ecc.md`	Geopolymer gel matrices possess 50–66 % higher nanometer specific surface area ($25\text{--}60\text{ m}^2/\text{g}$) than Portland cement	Liquid nitrogen porosimetry (LNP) and pore size distribution analysis	Section 3.2 & 3.3, Fig. 5-8, Table 4	verified_from_pdf
`02_concepts/strain_hardening_criteria.md`	Ambient-cured geopolymer elements exhibit vertical pore gradation with void volume decreasing from 32 % at the top to 8 % at the bottom	Pore detection image analysis (PDIA) and AVPV depth-profiling	Section 3.1 & 3.4, Fig. 9-12, Table 5	verified_from_pdf

Verification status

PDF preserved: yes (negahban-2021-pore-gradation-portland-geopolymer.pdf)
Text extracted: yes (full_text/negahban-2021-pore-gradation-portland-geopolymer_full_text.md)
DOI verified: yes (10.1016/j.cemconcomp.2021.104141)
Metadata verified: yes (Cem. Concr. Compos., Vol. 122, 104141, 2021)
Claim-evidence matrix ready: yes

Cautions

Top-layer pore coarsening in ambient-cured geopolymer members indicates that surface sealing or curing membranes are essential to prevent premature desiccation and surface carbonation.
High nano-porosity does not imply high permeability, because ink-bottle gel pores ($< 10\text{ nm}$) restrict fluid percolation.