Optimization of Metakaolin-Based Geopolymer Composite for Repair Application
Abstract
1. Introduction
2. Experimental Program
2.1. Materials
2.2. Mixture Proportions
2.3. Samples Preparation
2.4. Test Methods
3. Results and Discussion
3.1. Flowability
3.2. Compressive Strength
3.3. Flexural and Splitting Tensile Strengths
3.4. UPV
4. Optimization of GP Mixtures
4.1. Taguchi Approach
4.2. Analysis of Variance
4.3. Validation of the Optimum Mix—Bond Strength Testing
5. Conclusions
- The flowability of the GP mixtures was found to increase with a higher alkaline activator-to-metakaolin ratio (A/M). ANOVA analysis confirmed that A/M had the most pronounced effect on workability, whereas the impact of other parameters was statistically insignificant.
- The compressive strength of MK-based geopolymer mortars surpassed 30 MPa when the A/M ratio, S/H ratio, SH molarity, and curing temperature were within the ranges of 1.0–1.4, 2.0–3.0, 14–16 M, and 45–60 °C, respectively. These conditions demonstrate the suitability of such combinations for targeted repair applications, particularly when compared to conventional cement-based mortars.
- The results for flexural strength, splitting tensile strength, and ultrasonic pulse velocity (UPV) aligned with those of compressive strength. Mixtures produced with higher A/M ratios and elevated curing temperatures exhibited enhanced performance, likely due to a more compact and refined matrix structure.
- The ANOVA results confirmed that A/M ratio and SH molarity were the most significant parameters affecting the mechanical behavior of the GP mixtures. Conversely, the SS/SH ratio and curing temperature showed comparatively lower influence on strength development within the tested range.
- The Taguchi method revealed that a GP mix with an A/M ratio of 1.4, SS/SH ratio of 2, sodium hydroxide molarity of 16, and a curing temperature of 60 °C delivered optimal performance. This optimized mix achieved compressive strengths of 39.9 MPa at 7 days and 41.0 MPa at 14 days, matching the strength levels of the cement-based reference mortar, even though it contained less binder (377–427 kg/m3 for the geopolymer compared to 464 kg/m3 for cement).
- GP mortars demonstrated superior bond strength compared to traditional cement-based composites. This can be attributed to the enhanced chemical bonding and denser matrix provided by the geopolymer structure, which improves the interfacial adhesion between layers or substrates.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Al2O3 | NaOH | SiO2 | Na2O | K2O | Fe2O3 | TiO2 | MgO | CaO | LOI | Density | |
---|---|---|---|---|---|---|---|---|---|---|---|
Cement | 4.3 | - | 21.4 | 0.52 | - | 3.1 | - | 2.7 | 62.9 | 1.84 | 3.15 |
MK | 38.5 | - | 58.7 | - | 0.85 | 0.72 | 0.5 | 0.38 | 0.2 | 1.67 | 2.6 |
Parameters, P | Levels | ||
---|---|---|---|
1 | 2 | 3 | |
P1: A/M, by mass | 1 | 1.2 | 1.4 |
P2: S/H, by mass | 2 | 2.5 | 3 |
P3: SH molarity | 12 | 14 | 16 |
P4: Curing temperature | 30 | 45 | 60 |
Mix ID | Mix Codification * | A/M | S/H | SH Molarity | Temperature (°C) |
---|---|---|---|---|---|
G1 | 1.0A/M-2.0S/H-12M-30T | 1 | 2 | 12 | 30 |
G2 | 1.0A/M-2.5S/H-14M-45T | 1 | 2.5 | 14 | 45 |
G3 | 1.0A/M-3.0S/H-16M-60T | 1 | 3 | 16 | 60 |
G4 | 1.2A/M-2.5S/H-16M-30T | 1.2 | 2.5 | 16 | 30 |
G5 | 1.2A/M-3.0S/H-12M-45T | 1.2 | 3 | 12 | 45 |
G6 | 1.2A/M-2.0S/H-14M-60T | 1.2 | 2 | 14 | 60 |
G7 | 1.4A/M-3.0S/H-14M-30T | 1.4 | 3 | 14 | 30 |
G8 | 1.4A/M-2.0S/H-16M-45T | 1.4 | 2 | 16 | 45 |
G9 | 1.4A/M-2.5S/H-12M-60T | 1.4 | 2.5 | 12 | 60 |
Mix ID | Compressive Strength (MPa) | Increase in Strength | |||||
---|---|---|---|---|---|---|---|
7-Day | 14-Day | 28-Day | 56-Day | 7–14 Days (%) | 7–28 Days (%) | 7–56 Days (%) | |
C1 | 13.7 | 15.2 | 16.9 | 17.3 | 10.7 | 23.0 | 26.1 |
C2 | 19.7 | 22.2 | 24.9 | 26.8 | 12.7 | 26.6 | 36.2 |
1.0A/M-2.0S/H-12M-30T | 22.8 | 23.4 | 23.8 | 24.0 | 2.5 | 4.2 | 5.1 |
1.0A/M-2.5S/H-14M-45T | 22.7 | 29.4 | 30.3 | 30.5 | 29.6 | 33.8 | 34.6 |
1.0A/M-3.0S/H-16M-60T | 29.5 | 36.3 | 36.4 | 36.5 | 23.2 | 23.5 | 23.7 |
1.2A/M-2.5S/H-16M-30T | 31.0 | 33.0 | 33.4 | 33.5 | 6.5 | 7.8 | 8.1 |
1.2A/M-3.0S/H-12M-45T | 15.5 | 16.0 | 16.1 | 16.2 | 3.2 | 4.1 | 4.5 |
1.2A/M-2.0S/H-14M-60T | 33.8 | 34.8 | 35.3 | 35.5 | 3.0 | 4.3 | 4.9 |
1.4A/M-3.0S/H-14M-30T | 20.2 | 27.2 | 29.3 | 29.6 | 34.7 | 45.5 | 46.8 |
1.4A/M-2.0S/H-16M-45T | 34.0 | 36.6 | 36.6 | 36.6 | 7.6 | 7.6 | 7.6 |
1.4A/M-2.5S/H-12M-60T | 24.3 | 24.4 | 24.5 | 24.5 | 0.4 | 0.7 | 0.7 |
Property | Contribution (%) | |||
---|---|---|---|---|
A/M | S/H | SH Molarity | Temperature | |
Flow | 87 | 0.1 | 11.1 | 1.8 |
Compressive strength | 3.3 | 11.9 | 74.6 | 10.2 |
Flexural strength | 6.2 | 14.9 | 51.7 | 27.2 |
Splitting tensile strength | 0.9 | 5.7 | 76.3 | 17.1 |
UPV | 6.3 | 1.0 | 89.8 | 2.9 |
Results | Min (Mix G5) | Max (Mix G3) | C2 | Optimum GP |
---|---|---|---|---|
7-day fc (MPa) | 15.5 | 29.5 | 19.7 | 39.9 |
14-day fc (MPa) | 16.0 | 36.3 | 22.2 | 41.0 |
7-day fr (MPa) | 4.5 | 9.6 | 6.2 | 9.3 |
14-day fr (MPa) | 5.0 | 10.9 | 7.3 | 10.8 |
7-day fs (MPa) | 3.6 | 5.5 | 5.8 | 8.0 |
14-day fs (MPa) | 4.1 | 9.0 | 7.4 | 10.0 |
7-day UPV (m/s) | 2542 | 3096 | 3746 | 2994.3 |
14-day UPV (m/s) | 2585 | 3126 | 3845 | 3025.8 |
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Hawa, L.; El-Mir, A.; Khatib, J.; Nasr, D.; Assaad, J.; Elkordi, A.; Ezzedine El Dandachy, M. Optimization of Metakaolin-Based Geopolymer Composite for Repair Application. J. Compos. Sci. 2025, 9, 527. https://doi.org/10.3390/jcs9100527
Hawa L, El-Mir A, Khatib J, Nasr D, Assaad J, Elkordi A, Ezzedine El Dandachy M. Optimization of Metakaolin-Based Geopolymer Composite for Repair Application. Journal of Composites Science. 2025; 9(10):527. https://doi.org/10.3390/jcs9100527
Chicago/Turabian StyleHawa, Layal, Abdulkader El-Mir, Jamal Khatib, Dana Nasr, Joseph Assaad, Adel Elkordi, and Mohamad Ezzedine El Dandachy. 2025. "Optimization of Metakaolin-Based Geopolymer Composite for Repair Application" Journal of Composites Science 9, no. 10: 527. https://doi.org/10.3390/jcs9100527
APA StyleHawa, L., El-Mir, A., Khatib, J., Nasr, D., Assaad, J., Elkordi, A., & Ezzedine El Dandachy, M. (2025). Optimization of Metakaolin-Based Geopolymer Composite for Repair Application. Journal of Composites Science, 9(10), 527. https://doi.org/10.3390/jcs9100527