Effects of Al/Na and Si/Na Molar Ratios on the Alkalinity of Metakaolin-Based Geopolymer Pore Solutions
Abstract
:1. Introduction
2. Experimental Setup
2.1. Raw Materials
2.2. Mix Design
2.3. Specimen Manufacture
2.4. Test and Analysis Methods
2.4.1. Pore Solution Test
2.4.2. Microstructure Test
2.4.3. Phase Composition Analysis
3. Results and Discussion
3.1. The pH Analysis of the Pore Solutions
3.1.1. Effects of the Al/Na Ratio
3.1.2. Effects of the Si/Na Ratio
3.2. Analysis of Compressive Strength
3.2.1. Effects of the Al/Na Ratio
3.2.2. Effects of the Si/Na Ratio
3.3. Geopolymerization
3.3.1. Study of Reaction Levels under Changes in Al/Na Ratio
3.3.2. Study of Reaction Levels under Changes in Si/Na Ratio
3.4. Microstructure Analysis
3.4.1. SEM Diagrams and Pore Structures with Different Al/Na Ratios
3.4.2. SEM Diagrams and Pore Structures with Different Si/Na Ratios
3.5. Phase Composition Analysis
3.5.1. Changes in Phase Composition with Changes in Al/Na Ratio
3.5.2. Changes in Phase Composition with Changes in Si/Na Ratio
4. Conclusions
- With an increase in the Al/Na ratio, the Al contents of the systems increased and more OH− was consumed to generate AlO4 tetrahedrons, so the residual OH− contents after the reactions decreased and the pH of the pore solutions continued to decrease.
- With an increase in the Si/Na ratio, the alkalinity of the initiator became weaker, but the amount of excipient increased and the total OH− contents in the systems remained almost unchanged. The OH− concentrations on the surfaces of the raw material particles decreased, resulting in lower reaction levels and less OH− being consumed. Therefore, the residual OH− contents after the reactions increased and the pH of the pore solutions increased.
- The compressive strength of the geopolymers first increased and then decreased with an increase in the Al/Na ratio. The highly active Al increased the hydration reaction levels, which made the geopolymer structures become denser and demonstrate higher compressive strength. The Al components in the systems were excessive and the alkali contents gradually decreased when the Al/Na ratio was too high, which meant that the reaction levels and compressive strength of the geopolymers decreased.
- The compressive strength of the geopolymers gradually decreased with an increase in the Si/Na ratio. An increase in the Si/Na ratio led to a decrease in the alkali contents in the systems and the amount of metakaolin. Then, the reaction rates and levels of geopolymers decreased, so the compressive strength of the geopolymers also decreased.
- The exothermic reaction rates and the cumulative exothermic reactions of the geopolymers first increased and then gradually slowed down with an increase in the Al/Na ratio. This showed that an increase in the Al/Na ratio made the reaction levels first increase and then decrease. The exothermic reaction rates and the cumulative exothermic reaction of the geopolymers gradually decreased with an increase in the Si/Na ratio, which indicated that an increase in the Si/Na ratio made the reaction levels decrease.
- The SEM and MIP results showed that the smaller the pH value of a geopolymer pore solution, the denser the microstructure. Thus, the microstructures had good correlations with the changes in the pH values of the geopolymer pore solutions. The phase compositions after the hydration reactions were basically the same since the Al/Na and Si/Na ratios mainly affected the reaction levels of the geopolymers.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Raw Material | SiO2 | Al2O3 | Fe2O3 | MgO | Na2O | K2O | Others |
---|---|---|---|---|---|---|---|
Amount (%) | 54.5 | 43 | 1.0 | 0.8 | 0.1 | 0.4 | 0.2 |
Sample | Al/Na | Si/Na | Sodium Silicate Dosage (g) | NaOH Dosage (g) | Amount of Deionized Water (g) |
---|---|---|---|---|---|
A1 | 1.0 | 2.0 | 175.89 | 14.74 | 26.83 |
A2 | 1.1 | 141.23 | 15.42 | 28.19 | |
A3 | 1.2 | 112.36 | 15.98 | 29.32 | |
A4 | 1.3 | 87.93 | 16.45 | 30.28 | |
A5 | 1.4 | 66.93 | 16.86 | 31.10 | |
S1 | 1.3 | 1.8 | 58.61 | 19.62 | 36.25 |
S2 | 1.9 | 73.27 | 18.03 | 33.26 | |
S3 | 2.0 | 87.93 | 16.45 | 30.28 | |
S4 | 2.1 | 102.59 | 14.87 | 27.30 | |
S5 | 2.2 | 117.25 | 13.29 | 24.31 |
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Han, W.; Lv, Y.; Wang, S.; Qiao, J.; Zou, C.; Su, M.; Peng, H. Effects of Al/Na and Si/Na Molar Ratios on the Alkalinity of Metakaolin-Based Geopolymer Pore Solutions. Materials 2023, 16, 1929. https://doi.org/10.3390/ma16051929
Han W, Lv Y, Wang S, Qiao J, Zou C, Su M, Peng H. Effects of Al/Na and Si/Na Molar Ratios on the Alkalinity of Metakaolin-Based Geopolymer Pore Solutions. Materials. 2023; 16(5):1929. https://doi.org/10.3390/ma16051929
Chicago/Turabian StyleHan, Weiwei, Yigang Lv, Shiyu Wang, Jie Qiao, Chaosheng Zou, Miao Su, and Hui Peng. 2023. "Effects of Al/Na and Si/Na Molar Ratios on the Alkalinity of Metakaolin-Based Geopolymer Pore Solutions" Materials 16, no. 5: 1929. https://doi.org/10.3390/ma16051929