PSI - Issue 67

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Hwan Lee et al. / Procedia Structural Integrity 67 (2025) 107–114 Author name / Structural Integrity Procedia 00 (2024) 000 – 000

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3. CONCLUSIONS Nanomaterials have demonstrated significant potential in enhancing the strength and durability of concrete. This paper evaluates the effectiveness of nano metakaolin (NMK) and carbon nanotubes (CNTs) in reducing expansion caused by the alkali-silica reaction (ASR). It was seen that replacing cement with NMK at all dosages improved ASR resistance, notably, a 10% replacement dosage-controlled expansion to below acceptable limits, even with highly reactive siliceous aggregates. Conversely, a low dosage of CNTs (0.01%) slightly increased the ASR expansion, while higher dosages (0.03% and 0.05%) resulted in reduced expansion, though not to the acceptable expansion limit of 0.1%. The mechanisms behind the ASR resistance improvement appear to differ between the nanomaterials, with NMK densifying the microstructure through pozzolanic reactions, whereas CNTs function mechanically to reduce expansion through the 'bridging effect ’ . These findings underscore the potential of NMK and CNTs to enhance ASR resistance through various mechanisms, including increased nucleation sites, pozzolanic activity, microstructural densification for NMK, and increased nucleation sites and bridging effect for CNTs. Future work will focus on optimizing the dosages of NMK and CNT to balance cost and ASR resistance effectively and gaining more insight into the underlying mechanisms of ASR mitigation of the nanomaterials by analyzing cement hydration with calorimetry, thermogravimetric analysis, and scanning electron microscopy. References Abo-El-Enein, S. A., M. S. Amin, F. I. El- Hosiny, S. Hanafi, T. M. ElSokkary, and M. M. Hazem. 2014. “Pozzolanic and hydraulic activity of nano- metakaolin.” HBRC J. , 10 (1): 64 – 72. Informa UK Limited. https://doi.org/10.1016/j.hbrcj.2013.09.006. Al- Shmaisani, S., R. D. Kalina, R. Douglas Ferron, and M. C. G. Juenger. 2022. “Assessment of blended coal source fly ashes and blended fly ashes.” Constr. Build. Mater. , 342: 127918. Elsevier. https://doi.org/10.1016/J.CONBUILDMAT.2022.127918. Aquino, W., D. A. Lange, and J. Olek. 2001. “The influence of metakaolin and silica fume on the chemistry of alkali - silica reaction products.” Cem. Concr. Compos. , 23. ASTM C 305. 1998. “Standard Practice for Mechanical mixing of hydraulic cement pastes and mortars of plastic consistency.” ASTM Int. , 14 (2): 147. https://doi.org/10.1177/089033449801400218. ASTM C 595. 2003. “Standard Specification for Blended Hydraulic Cements.” ASTM Int. , (C595): 1 – 6. https://doi.org/10.1520/C0595. ASTM C109. 1993. “Standard test method for compressive strength of hydraulic cement mortars.” ASTM Int. , 04: 1 – 7. https://doi.org/10.1520/C0109. ASTM C1260. 2014. “Standard Test Method for Potential Alkali Reactivity of Aggregates ( Mortar - Bar Method).” Annu. B. ASTM Stand. Vol. 04.02 , 1 – 5. https://doi.org/10.1520/C1260-22.2. ASTM C1293. 2015. “Standard test method for determination of length change of concrete due to alkali - silica reaction.” Annu. B. ASTM Stand. , 1 – 7. https://doi.org/10.1520/C1293-20A.2. ASTM C1567- 23. 2005. “Standard Test Method for Determining the Potential Alkali -Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar- Bar Method).” Annu. B. ASTM Stand. , 04.02: 774 – 778. https://doi.org/10.1520/C1567-23. ASTM C1876. 2019. “Standard Test Method for Electrical Resistivity or Conductivity of Concrete.” ASTM Int. , 98 – 100. https://doi.org/10.1520/C1876-19. Barbhuiya, S., and P. L. Chow. 2019. “Nanoscale mechanical properties of cement paste reinforced with short carbon nanotubes.” Proc. Ins , 172 (2): 63 – 70. Thomas Telford Ltd. https://doi.org/10.1680/JCOMA.17.00025. Cai, Y., D. Xuan, and C. S. Poon. 2019. “Effects of nano -SiO2 and glass powder on mitigating alkali- silica reaction of cement glass mortars.” Constr. Build. Mater. , 201: 295 – 302. Elsevier Ltd. https://doi.org/10.1016/j.conbuildmat.2018.12.186. Cheaptubes.com. n.d. “https://www.cheaptubes.com/product/multi -walled-carbon-nanotubes-10- 20nm/.” Demir, İ., B. Sivrikaya, O. Sevim, and M. Baran. 2020. “A study on ASR mitigation by optimized particle size distribution.” Constr. Build. Mater. , 261. https://doi.org/10.1016/j.conbuildmat.2020.120492. Fadzil, A. M., M. S. M. Norhasri, M. S. Hamidah, M. R. Zaidi, and J. M. Faizal. 2014. “Alteration of nano metakaolin for ultr a high performance concrete.” InCIEC 2013 , 887 – 894. Folliard, K. J., R. Barborak, T. Drimalas, L. Du, S. Garber, J. H. Ideker, T. Ley, S. Williams, M. C. G. Juenger, B. Fournier, and M. D. A. Thomas. 2006. Preventing ASR/DEF in New Concrete: Final Report . Texas Dep. Transp. Gong, F., Y. Takahashi, I. Segawa, and K. Maekawa. 2020. “Mechanical properties of concrete with smeared cracking by alkali -silica reaction