Pore Structure Characterization of Sodium Hydroxide Activated Slag Using Mercury Intrusion Porosimetry, Nitrogen Adsorption, and Image Analysis
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials and Mixtures
2.2. Methods
2.2.1. MIP
2.2.2. N2 Adsorption
2.2.3. SEM-Image Analysis
2.2.4. Solid Phase Growth
3. Results
3.1. Morphology of Hardened Sodium Hydroxide Activated Slag Samples
3.2. Degree of Reaction of Slag
3.3. Pore Structure of Sodium Hydroxide Activated Slag Pastes Determined by MIP
3.3.1. Total Porosity Derived from MIP
3.3.2. Pore Size Distribution Derived from MIP
3.3.3. Ink-Bottle Pore and Pore Connectivity Derived from MIP
3.4. Pore Structure of Sodium Hydroxide Activated Slag Pastes Determined by N2 Adsorption
3.5. Pore Structure of Sodium Hydroxide Activated Slag Pastes Characterized by Image Analysis
4. Discussion
4.1. Comparison of Pore Structure Determined by MIP and N2 Adsorption
4.2. Comparison of Pore Structure Derived from MIP and Image Analysis
4.3. A Brief Summary of MIP, N2 Adsorption, and Image Analysis in Characterizing the Pore Structure of Sodium Hydroxide Activated Slag
4.4. Microstructure Formation of Sodium Hydroxide Activated Slag Paste
4.5. Pore Space Filling Capacity
5. Conclusions
- MIP: The total porosity, from an initial value of 54.2%, drops about 70% within the first day and then decreases slowly with time to 7–10% at 360 days. The ink-bottle porosity decreases continuously with time, while the pore connectivity increases with time at early stages up to 28 days and then decreases until 360 days. For all the samples from 1 to 360 days, at most one peak that corresponds to gel pores was identified in the differential curves. As the Na2O content and curing age increase, the identified peak shifts to a smaller pore diameter.
- N2 adsorption: The porosity of small pores (<0.25 μm) increases with time at early stage, for example, up to 28 days for AAS4, and then decreases till 360 days. An increase of Na2O content leads to a lower porosity of small pores. In general, the differential curves show two peaks, and the trend that pore diameters of those two peaks vary with curing age depends on the content of Na2O.
- SEM-image analysis: The degree of reaction of slag is higher for samples with longer curing time and higher content of Na2O. About 50% of slag was reacted within the first day. The peak identified in the differential curves is found at about 1.6 μm, and it shows little change with increasing curing age and Na2O content.
- MIP vs. N2 adsorption: The comparison between differential curves at pore sizes smaller than 0.01 μm reveals damage resulting from high pressure during MIP measurement. The “ink-bottle” effect may lead to the absence of the second peak that corresponds to the capillary pores in the MIP results.
- Microstructure formation: The increase of Na2O content and curing age led to a reduced porosity and a refined microstructure. Conceptual models are proposed to describe the microstructure formation process, during which two layers of reaction products, e.g., outer C–(N–)A–S–H and inner C–(N)–A–S–H, grow successively around the reacting slag grains, while the secondary reaction products, such as the hydrotalcite phase, are formed in the empty coarse pore space.
- Pore space filling capacity: Sodium hydroxide activated slag has a higher pore space filling capacity than Portland cement. Along with the increases of Na2O content and curing age, the pore space filling capacity of sodium hydroxide activated slag decreases.
Supplementary Materials
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Oxide | SiO2 | CaO | Al2O3 | MgO | Fe2O3 | SO3 | K2O | TiO2 | L.I. * |
---|---|---|---|---|---|---|---|---|---|
Weight (%) | 32.91 | 40.96 | 11.85 | 9.23 | 0.46 | 1.61 | 0.33 | 1.00 | 1.15 |
Mix | Slag (g) | Na2O (g) | Water (g) |
---|---|---|---|
AAS4 | 100 | 4 | 40 |
AAS6 | 100 | 6 | 40 |
AAS8 | 100 | 8 | 40 |
Samples | 1 Day | 7 Days | 28 Days | 180 Days | 360 Days |
---|---|---|---|---|---|
AAS4 | 5.98 | 6.89 | 7.19 | 6.50 | 4.87 |
AAS6 | 3.85 | 3.46 | 2.45 | 1.57 | 1.81 |
AAS8 | 2.82 | 3.22 | 2.50 | 1.07 | 1.19 |
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Zuo, Y.; Ye, G. Pore Structure Characterization of Sodium Hydroxide Activated Slag Using Mercury Intrusion Porosimetry, Nitrogen Adsorption, and Image Analysis. Materials 2018, 11, 1035. https://doi.org/10.3390/ma11061035
Zuo Y, Ye G. Pore Structure Characterization of Sodium Hydroxide Activated Slag Using Mercury Intrusion Porosimetry, Nitrogen Adsorption, and Image Analysis. Materials. 2018; 11(6):1035. https://doi.org/10.3390/ma11061035
Chicago/Turabian StyleZuo, Yibing, and Guang Ye. 2018. "Pore Structure Characterization of Sodium Hydroxide Activated Slag Using Mercury Intrusion Porosimetry, Nitrogen Adsorption, and Image Analysis" Materials 11, no. 6: 1035. https://doi.org/10.3390/ma11061035
APA StyleZuo, Y., & Ye, G. (2018). Pore Structure Characterization of Sodium Hydroxide Activated Slag Using Mercury Intrusion Porosimetry, Nitrogen Adsorption, and Image Analysis. Materials, 11(6), 1035. https://doi.org/10.3390/ma11061035