The Effect of Microwave Curing on the Strength Development of Class-F Fly Ash-Based Geopolymer Mortar

Öz

This study investigates the influence of microwave (MW) curing on the strength development of geopolymer. Since applying conventional oven heat curing makes the heat moves from outer edge to the center of specimen and leads to a non-uniform of distributing heat within the specimen, which effects on the mechanical properties of the geopolymer. On the other hand, the use of MW reduces the curing time and allows to uniform heat distribution within samples and provides higher mechanical properties in a short period. The influence of conventional heat curing and MW curing on class F fly ash based geopolymer activated with sodium hydroxide and sodium metasilicate was investigated. The conventional heat curing was applied at 75 and 90°C for 6 and 24 hours; on the other hand, additional MW curing was applied for a different period (5-60 minutes) and different energy level (100, 180 and 300W) on hardened geopolymer samples cured with conventional oven curing. The results show that the use of conventional heat curing for 6 hours followed by MW curing gave higher or equivalent strength compared to only conventional heat curing. While 24 hours conventional heat curing result with a geopolymer having 39.1 MPa compressive strength, 6 hours conventional heat curing followed by 1 hour MW curing at 180W energy level results with a geopolymer with compressive strength in the order of 80 MPa.

Anahtar Kelimeler

• Fly ash
• geopolymer
• microwave curing
• strength

The Effect of Microwave Curing on the Strength Development of Class-F Fly Ash-Based Geopolymer Mortar

Öz

Bu çalışmada, mikrodalga (MW) kürünün geopolimerin dayanım gelişimi üzerindeki etkisi araştırılmıştır. Geleneksel ısıyla fırın küründe, ısı numunenin dış kenardan numune merkezine doğru hareket etmekte ve bu durum numune üzerine üniform olmayan bir ısınmaya neden olarak geopolimerlerin mekanik özelliklerini etkilemektedir. Öte yandan, MW kullanımı numuneler içinde homojen ısı dağılımına olanak sağlayarak kürleme süresini azaltmakta ve kısa sürede daha yüksek mekanik özellikler elde edilmesini sağlamaktadır. Çalışmada sodyum hidroksit ve sodyum metasilikat ile aktive edilmiş F sınıfı uçucu kül bazlı geopolimerler üzerinde geleneksel ısıl kür ve MW kürü etkileri araştırılmıştır. Geleneksel ısıl kür 75 ve 90°C'de 6 ve 24 saat süreyle numunelere uygulanmıştır. Mikrodalga kürü ise geleneksel ısıl kür ile kürlenen sertleştirilmiş geopolimer numunelere farklı süre (5-60 dakika) ve farklı enerji seviyelerinde (100, 180 ve 300W) ilave olarak uygulanmıştır. Elde edilen sonuçlara göre 6 saat boyunca geleneksel ısıl kür ile sertleşen numunelere MW kürü uygulanması durumunda, yalnızca geleneksel ısıl kür ile dayanım kazanan numunelere kıyasla daha yüksek veya eşdeğer bir dayanım elde edildiği görülmüştür. 24 saat geleneksel ısıl kür sonucu 39,1 MPa basınç dayanımına ulaşan bir geopolimer, 6 saat geleneksel ısıl kür sonrası 180W enerji seviyesinde 1 saat MW kürüne tabi tutulduğunda 80 MPa civarında basınç dayanımı elde edilmiştir.

Anahtar Kelimeler

• Uçucu Kül
• Geopolymer
• Microwave curing
• Strength

Kaynakça

1. References [1] N. Müller and J. Harnisch, “A Blueprint for a Climate-Friendly Cement Industry: How to Turn Around the Trend of Cement Related Emissions in the Developing World,” 2008.
2. [2] D. Hardjito and B. V. Rangan, “Development and properties of low-calcium fly ash-based geopolymer concrete,” 2005.
3. [3] W. K. W. Lee and J. S. J. Van Deventer, “The effect of ionic contaminants on the early-age properties of alkali-activated fly ash-based cements,” Cem. Concr. Res., 2002, doi: 10.1016/S0008-8846(01)00724-4.
4. [4] P. Duxson, J. L. Provis, G. C. Lukey, and J. S. J. van Deventer, “The role of inorganic polymer technology in the development of ‘green concrete,’” Cem. Concr. Res., 2007, doi: 10.1016/j.cemconres.2007.08.018.
5. [5] J. L. Provis and J. S. J. Van Deventer, Geopolymers: Structures, processing, properties and industrial applications. 2009.
6. [6] L. Vickers, A. van Riessen, and W. Rickard, Fire-resistant Geopolymers: Role of Fibres and Fillers to Enhance Thermal Properties. Singapore: Springer, 2015.
7. [7] A. Palomo, M. T. Blanco-Varela, M. L. Granizo, F. Puertas, T. Vazquez, and M. W. Grutzeck, “Chemical stability of cementitious materials based on metakaolin,” Cem. Concr. Res., 1999, doi: 10.1016/S0008-8846(99)00074-5.
8. [8] T. Bakharev, “Durability of geopolymer materials in sodium and magnesium sulfate solutions,” Cem. Concr. Res., 2005, doi: 10.1016/j.cemconres.2004.09.002.

9. [9] C. O.-P. Guillaume Haberta, “Recent update on the environmental impact of geopolymers,” RILEM Tech. Lett., vol. 1, pp. 17–23, 2016.
10. [10] J. Somaratna, D. Ravikumar, and N. Neithalath, “Response of alkali activated fly ash mortars to microwave curing,” Cem. Concr. Res., vol. 40, no. 12, pp. 1688–1696, 2010, doi: 10.1016/j.cemconres.2010.08.010.
11. [11] TS EN 450-1, Fly ash for concrete - Part 1: Definition, specifications and conformity criteria. Ankara: TSE, 2013.
12. [12] ASTM C618, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete. merican Society for Testing and Material, 2014.
13. [13] C. D. A. Erion Luga, “Strength Properties of Slag/Fly Ash Blends Activated with Sodium Metasilicate and Sodium Hydroxide+Silica Fume,” Period. Polytech. Civ. Eng., vol. 60, no. 2, pp. 223–228, 2016.
14. [14] F. Khaleel, “The Effect of Microwave Curing on the Strength Development of F Class Fly Ash Based Geopolymer,” Graduate School of Natural and Applied Sciences, 2019.
15. [15] TS EN 1015-11, Mortar Testing Method, Part 11. Measurement of Compressive and Flexural Tensile Strength of Mortar. Ankara: TSE, 2000.
16. [16] TS EN 196-1, Methods of testing cement—part:1 determination of strength. TSE, 2016.
17. [17] B. H. Mo, H. Zhu, X. M. Cui, Y. He, and S. Y. Gong, “Effect of curing temperature on geopolymerization of metakaolin-based geopolymers,” Appl. Clay Sci., 2014, doi: 10.1016/j.clay.2014.06.024.
18. [18] K. Somna, C. Jaturapitakkul, P. Kajitvichyanukul, and P. Chindaprasirt, “NaOH-activated ground fly ash geopolymer cured at ambient temperature,” Fuel, vol. 90, no. 6, pp. 2118–2124, 2011, doi: 10.1016/j.fuel.2011.01.018.
19. [19] G. Görhan and G. Kürklü, “The influence of the NaOH solution on the properties of the fly ash-based geopolymer mortar cured at different temperatures,” Compos. Part B Eng., vol. 58, pp. 371–377, 2014, doi: 10.1016/j.compositesb.2013.10.082.
20. [20] A. M. Mustafa Al Bakria, H. Kamarudin, M. Bin Hussain, I. Khairul Nizar, Y. Zarina, and A. R. Rafiza, “The effect of curing temperature on physical and chemical properties of geopolymers,” Phys. Procedia, vol. 22, pp. 286–291, 2011, doi: 10.1016/j.phpro.2011.11.045.
21. [21] C. D. Atiş, E. B. Görür, O. Karahan, C. Bilim, S. Ilkentapar, and E. Luga, “Very high strength (120 MPa) class F fly ash geopolymer mortar activated at different NaOH amount, heat curing temperature and heat curing duration,” Constr. Build. Mater., vol. 96, pp. 673–678, 2015, doi: 10.1016/j.conbuildmat.2015.08.089.
22. [22] A. Graytee, J. G. Sanjayan, and A. Nazari, “Development of a high strength fly ash-based geopolymer in short time by using microwave curing,” Ceram. Int., 2018, doi: 10.1016/j.ceramint.2018.02.001.