Mechanical Properties and Microstructural Characterization of Metakaolin Geopolymers Based on Orthogonal Tests
Abstract
:1. Introduction
2. Experimental Materials and Methods
2.1. Materials
2.1.1. Metakonlin (MK)
2.1.2. Alkali Activator
2.2. Orthogonal Experimental Design
2.3. Specimen Preparation
2.4. Test Methods
2.4.1. Mechanical Properties Testing
2.4.2. Microscopic Mechanism Analysis
2.5. Polar Difference Methodology
3. Results and Discussion
3.1. Mechanical Properties Analysis
3.2. Analysis of Influencing Factors
3.3. Microscopic Mechanism Analysis
3.3.1. XRD Analysis
3.3.2. SEM Analysis
3.3.3. FTIR Analysis
4. Conclusions
- (1)
- Both the Na-based and K-based geopolymers could achieve high compressive and flexural strengths. They all had early-strength properties, with mechanical strengths of up to 80% of the 28-day strength at 7 days, but the mechanical properties of the K-based geopolymers were better than those of the Na-based geopolymers.
- (2)
- For the compressive strength, the increase in alkaline solution concentration increased the compressive strength of the geopolymers, and the Na-based geopolymers always maintained a positive relationship, while the K-based showed an increasing and then decreasing trend. For the mass ratio of alkali activator to metakaolin and Na2SiO3/MOH, the compressive strength of both geopolymers showed an increasing and then decreasing trend.
- (3)
- For the flexural strength, the increase in the concentration of alkali solution had a positive correlation with the promotion effect on both Na-based and K-based geopolymers. With the increase in the Na2SiO3/MOH mass ratio, the flexural strength of both site geopolymers showed a trend of increasing and then decreasing. Increasing the mass of the alkali activator negatively affected the flexural strength of the K-based geopolymers, while it showed a trend of increasing and then decreasing for the Na-based geopolymers.
- (4)
- Microscopic analysis showed that increasing the concentration of the alkaline solution could promote the dissolution of silicon–aluminum raw materials and make the reaction more complete. Properly adjusting the ratio of Na2SiO3 to MOH and the mass ratio of alkali activator to metakaolin could produce more hydrated silicoaluminate gels and C-A-S-H, reduce unreacted metakaolin and microcracks, and cause the structure of the geopolymer to be denser.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Content | SiO2 | Al2O3 | CaO | K2O | SO3 | P2O5 | MgO | Na2O | Fe2O3 | Total |
---|---|---|---|---|---|---|---|---|---|---|
MK | 53.70 | 35.30 | 3.88 | 1.45 | 1.16 | 0.40 | 1.12 | 1.45 | 0.25 | 99.51 |
Levels | A: Alkaline Solution Concentration (mol/L) | B: Alkali Activator/Binding Material (Mass Ratio) | C: M2SiO3/MOH (Mass Ratio) |
---|---|---|---|
1 | 8 | 0.7 | 1.5 |
2 | 10 | 0.8 | 2 |
3 | 12 | 0.9 | 2.5 |
4 | 14 | 1.0 | 3 |
No. | Factors | Compressive Strength (MPa) | Flexural Strength (MPa) | ||||
---|---|---|---|---|---|---|---|
A | B | C | 7 Days | 28 Days | 7 Days | 28 Days | |
N1 | 8 M | 0.7 | 1.5 | 10.20 | 26.67 | 4.75 | 5.65 |
N2 | 8 M | 0.8 | 2 | 15.27 | 32.53 | 4.41 | 5.81 |
N3 | 8 M | 0.9 | 2.5 | 30.72 | 36.75 | 5.21 | 6.54 |
N4 | 8 M | 1 | 3 | 21.32 | 34.58 | 1.10 | 1.85 |
N5 | 10 M | 0.7 | 2 | 36.66 | 42.53 | 5.84 | 6.46 |
N6 | 10 M | 0.8 | 1.5 | 47.55 | 59.18 | 7.03 | 7.65 |
N7 | 10 M | 0.9 | 3 | 38.42 | 57.81 | 6.56 | 7.29 |
N8 | 10 M | 1 | 2.5 | 22.57 | 41.14 | 4.08 | 4.62 |
N9 | 12 M | 0.7 | 2.5 | 48.96 | 56.56 | 6.09 | 6.72 |
N10 | 12 M | 0.8 | 3 | 49.89 | 60.16 | 5.72 | 6.62 |
N11 | 12 M | 0.9 | 1.5 | 55.25 | 63.7 | 5.42 | 6.17 |
N12 | 12 M | 1 | 2 | 41.40 | 50.88 | 5.34 | 6.05 |
N13 | 14 M | 0.7 | 3 | 45.17 | 51.73 | 4.85 | 5.76 |
N14 | 14 M | 0.8 | 2.5 | 49.48 | 60.91 | 7.51 | 8.10 |
N15 | 14 M | 0.9 | 2 | 57.09 | 64.18 | 7.63 | 8.28 |
N16 | 14 M | 1 | 1.5 | 46.59 | 56.49 | 5.78 | 6.39 |
No. | Factors | Compressive Strength (MPa) | Flexural Strength (MPa) | ||||
---|---|---|---|---|---|---|---|
A | B | C | 7 Days | 28 Days | 7 Days | 28 Days | |
K1 | 8 M | 0.7 | 1.5 | 15.09 | 29.81 | 5.55 | 6.65 |
K2 | 8 M | 0.8 | 2 | 15.45 | 38.41 | 5.12 | 6.05 |
K3 | 8 M | 0.9 | 2.5 | 19.69 | 40.19 | 5.50 | 6.4 |
K4 | 8 M | 1 | 3 | 46.10 | 50.26 | 1.40 | 2.13 |
K5 | 10 M | 0.7 | 2 | 46.33 | 50.50 | 7.66 | 8.41 |
K6 | 10 M | 0.8 | 1.5 | 59.11 | 63.13 | 7.10 | 8.09 |
K7 | 10 M | 0.9 | 3 | 49.36 | 57.20 | 3.83 | 4.81 |
K8 | 10 M | 1 | 2.5 | 47.28 | 53.69 | 4.27 | 5.12 |
K9 | 12 M | 0.7 | 2.5 | 62.21 | 67.70 | 7.04 | 7.62 |
K10 | 12 M | 0.8 | 3 | 67.79 | 72.72 | 6.98 | 7.92 |
K11 | 12 M | 0.9 | 1.5 | 58.12 | 65.53 | 5.68 | 6.65 |
K12 | 12 M | 1 | 2 | 49.25 | 55.42 | 4.84 | 6.12 |
K13 | 14 M | 0.7 | 3 | 61.61 | 65.56 | 7.98 | 8.66 |
K14 | 14 M | 0.8 | 2.5 | 60.19 | 66.11 | 7.88 | 8.53 |
K15 | 14 M | 0.9 | 2 | 56.76 | 64.85 | 6.14 | 6.97 |
K16 | 14 M | 1 | 1.5 | 52.18 | 56.03 | 3.78 | 5.24 |
Factors | No. | Compressive Strength (MPa) | Flexural Strength (MPa) | ||||
---|---|---|---|---|---|---|---|
A | B | C | A | B | C | ||
K value | K1 | 77.51 | 140.99 | 159.59 | 15.47 | 21.53 | 22.98 |
K2 | 145.20 | 162.19 | 150.42 | 23.51 | 24.67 | 23.22 | |
K3 | 195.50 | 181.48 | 151.73 | 22.57 | 24.82 | 22.89 | |
K4 | 198.33 | 131.88 | 154.80 | 25.77 | 16.30 | 18.23 | |
k1 | 19.38 | 35.25 | 39.90 | 3.87 | 5.38 | 5.75 | |
k2 | 36.30 | 40.55 | 37.61 | 5.88 | 6.17 | 5.81 | |
k3 | 48.88 | 45.37 | 37.93 | 5.64 | 6.21 | 5.72 | |
k4 | 49.58 | 32.97 | 38.70 | 6.44 | 4.08 | 4.56 | |
R | 30.21 | 12.40 | 2.29 | 2.58 | 2.13 | 1.25 | |
Sequence | A > B > C | A > B > C | |||||
Preferred scheme | A4B3C1 | A4B3C2 |
Factors | No. | Compressive Strength (MPa) | Flexural Strength (MPa) | ||||
---|---|---|---|---|---|---|---|
A | B | C | A | B | C | ||
K value | K1 | 130.53 | 177.49 | 206.04 | 19.85 | 24.59 | 25.86 |
K2 | 200.66 | 212.78 | 190.12 | 26.02 | 28.18 | 27.03 | |
K3 | 231.30 | 222.44 | 195.36 | 25.56 | 28.71 | 25.98 | |
K4 | 233.31 | 183.09 | 204.28 | 28.96 | 18.91 | 21.52 | |
k1 | 32.63 | 44.37 | 51.51 | 4.96 | 6.15 | 6.47 | |
k2 | 50.17 | 53.20 | 47.53 | 6.51 | 7.05 | 6.76 | |
k3 | 57.83 | 55.61 | 48.84 | 6.39 | 7.18 | 6.50 | |
k4 | 58.33 | 45.77 | 51.07 | 7.24 | 4.73 | 5.38 | |
R | 25.70 | 11.24 | 3.98 | 2.28 | 2.45 | 1.38 | |
Sequence | A > B > C | B > A > C | |||||
Preferred scheme | A4B3C1 | A4B3C2 |
Factors | No. | Compressive Strength (MPa) | Flexural Strength (MPa) | ||||
---|---|---|---|---|---|---|---|
A | B | C | A | B | C | ||
K value | K1 | 96.33 | 185.24 | 184.50 | 17.57 | 28.23 | 22.11 |
K2 | 202.08 | 202.54 | 167.79 | 22.86 | 27.08 | 23.76 | |
K3 | 237.37 | 183.93 | 189.37 | 24.54 | 21.15 | 24.69 | |
K4 | 230.74 | 194.81 | 224.86 | 25.78 | 14.29 | 20.19 | |
k1 | 24.08 | 46.31 | 46.13 | 4.39 | 7.06 | 5.53 | |
k2 | 50.52 | 50.64 | 41.95 | 5.72 | 6.77 | 5.94 | |
k3 | 59.34 | 45.98 | 47.34 | 6.14 | 5.29 | 6.17 | |
k4 | 57.69 | 48.70 | 56.22 | 6.45 | 3.57 | 5.05 | |
R | 35.26 | 4.65 | 14.27 | 2.05 | 3.49 | 1.13 | |
Sequence | A > C > B | B > A > C | |||||
Preferred scheme | A3B2C4 | A4B1C3 |
Factors | No. | Compressive Strength (MPa) | Flexural Strength (MPa) | ||||
---|---|---|---|---|---|---|---|
A | B | C | A | B | C | ||
K value | K1 | 158.67 | 213.57 | 214.50 | 21.23 | 31.34 | 26.63 |
K2 | 224.52 | 241.58 | 209.18 | 26.43 | 30.59 | 27.55 | |
K3 | 262.58 | 227.77 | 227.69 | 28.31 | 24.83 | 27.67 | |
K4 | 252.55 | 215.40 | 246.95 | 29.4 | 18.61 | 23.52 | |
k1 | 39.67 | 53.39 | 53.63 | 5.31 | 7.84 | 6.66 | |
k2 | 56.13 | 60.40 | 52.30 | 6.61 | 7.65 | 6.89 | |
k3 | 65.65 | 56.94 | 56.92 | 7.08 | 6.21 | 6.92 | |
k4 | 63.14 | 53.85 | 61.74 | 7.35 | 4.65 | 5.88 | |
R | 25.98 | 7.01 | 9.44 | 2.04 | 3.18 | 1.04 | |
Sequence | A > C > B | B > A > C | |||||
Preferred scheme | A3B2C4 | A4B1C3 |
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Dai, S.; Wang, H.; An, S.; Yuan, L. Mechanical Properties and Microstructural Characterization of Metakaolin Geopolymers Based on Orthogonal Tests. Materials 2022, 15, 2957. https://doi.org/10.3390/ma15082957
Dai S, Wang H, An S, Yuan L. Mechanical Properties and Microstructural Characterization of Metakaolin Geopolymers Based on Orthogonal Tests. Materials. 2022; 15(8):2957. https://doi.org/10.3390/ma15082957
Chicago/Turabian StyleDai, Shoushuai, Hongguang Wang, Shuai An, and Long Yuan. 2022. "Mechanical Properties and Microstructural Characterization of Metakaolin Geopolymers Based on Orthogonal Tests" Materials 15, no. 8: 2957. https://doi.org/10.3390/ma15082957