Journal of the Korea Concrete Institute (콘크리트학회논문집)

Korea Concrete Institute (한국콘크리트학회)
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Microstructure and Strength of Class F Fly Ash based Geopolymer Containing Sodium Sulfate as an Additive

황산나트륨 첨가제에 따른 플라이애시 기반 지오폴리머의 미세구조 및 강도 특성

  • Jun, Yubin (School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST)) ;
  • Oh, Jae-Eun (School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST))
  • 전유빈 (울산과학기술대학교 도시환경공학부) ;
  • 오재은 (울산과학기술대학교 도시환경공학부)
  • Received : 2015.04.21
  • Accepted : 2015.05.20
  • Published : 2015.08.30
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Abstract

This paper presents an investigation of the mechanical and microstructural properties of Class F fly ash based geopolymer containing sodium sulfate as an additive. Sodium sulfate was used as an chemical additive at the dosage levels of 0, 2, 4, and 6wt% of fly ash. Sodium hydroxide and sodium silicate solutions were used to activate fly ash. The compressive strengths of geopolymer pastes were measured at the age of 28 days. The microstructures of the geopolymer pastes were examined using XRD, MIP and SEM tests. The additions of 2wt% and 4wt% sodium sulfate produced geopolymers with high strength, while increasing the dosage of levels to 6% resulted in almost no changes in strength, comparing with the control geopolymer. The optimum increase in strength was obtained with the addition of 4wt% sodium sulfate. As the amount of sodium sulfate is increased, no additional crystalline phase was detected and no change of amorphous phase indicated despite the change in the strength development. The increase in the strength was due to the change of pore size distribution in samples. As addition of sodium sulfate altered the morphologies of reactive productions and Si/Al ratios of the reaction products, the strengths were thus affected. It was found that the strengths of geopolymer were larger for lower Si/Al ratios of reaction products formed in samples. The optimal amount of sodium sulfate in the fly ash based geopolymer helps to improve mechanical properties of the geopolymer, on the other hand, the high percentage of sodium sulfate could exist as an impurity in the geopolymer and hinder the geopolymer reaction.

본 연구에서는 플라이애시 기반 지오폴리머에 황산나트륨을 첨가제로 사용하여 이에 대한 물리적 및 미세구조 특성을 분석하였다. 플라이애시 중량에 대해 0, 2, 4 및 6%를 황산나트륨으로 치환하였으며, 수산화나트륨과 액상규산나트륨(물유리)을 알칼리 활성화제로 사용하여 시편을 제작하였다. 재령 28일에 대한 압축강도, XRD, SEM 및 MIP 시험을 실시하였다. 황산나트륨 2wt% 및 4wt% 첨가는 플라이애시 기반 지오폴리머의 강도를 증진시켰지만, 6wt% 첨가는 강도 향상에 거의 영향을 주지 않는 것으로 나타났다. 강도 증진에 대한 황산나트륨의 적정 치환율이 있는 것으로 나타났으며, 압축강도에 대한 황산나트륨의 최적의 치환율은 4wt%인 것으로 판단된다. 황산나트륨 치환율이 증가함에 따라, 강도 증진 효과가 다름에도 불구하고 시편 내에 비결정질(amorphous phase) 뿐만 아니라 결정질(crystalline phase)에서 뚜렷한 차이가 없는 것으로 나타났다. 황산나트륨으로 치환하였을 경우, 플라이애시 기반 지오폴리머 내의 공극의 분포를 변화시킴에 따라 강도증진에 효과가 있는 것으로 판단된다. 황산나트륨 첨가는 시편 내의 생성된 반응생성물의 형상 및 Si/Al를 다르게 하여 강도에 영향을 미친 것으로 판단된다. 황산나트륨 치환에 따른 지오폴리머 내에 생성된 반응생성물의 Si/Al가 낮을수록 지오폴리머의 강도가 큰 것으로 나타났다. 황산나트륨 적정치환량은 지오폴리머의 반응생성물을 효과적으로 변화시켜 물리적 성질 향상에 기여를 하지만, 적정량 이상의 치환율 사용으로 변화된 지오폴리머 생성물은 matrix 내에서 불순물로 존재하여 강도 증진을 방해할 수 있는 가능성이 있는 것으로 판단된다.

Keywords

References

  1. Bakharev, T., "Geopolymeric materials prepared using Class F fly ash and elevated temperature curing", Cement and Concrete Research, Vol.35, 2005, pp.1224-1232. https://doi.org/10.1016/j.cemconres.2004.06.031
  2. Somna, K., Jatruapitakkul, C., Kajitvichyanukul, P., and Chindaprasirt, P., "NaOH-activated ground fly ash geopolymer cured at ambient temperature", Fuel, Vol.90, No.6, 2011, pp.2118-2124. https://doi.org/10.1016/j.fuel.2011.01.018
  3. Bondar, D., Lynsdale, C. J., Milestone, N. B., Hassani, N., and Ramezanianpour, A. A., "Effect of type, form, and dosage of activators on strength of alkali-activated natural pozzolans", Cement and Concrete Composites, Vol.33, No.2, 2011, pp.251-260. https://doi.org/10.1016/j.cemconcomp.2010.10.021
  4. Cho, Y. K., Moon, G. D., La, J. M., and Jung, S. H., "Effect of curing conditions on the strength of fly-ash based geopolymer", Journal of the Korea Concrete Institute, Vol.26, No.4, 2014, pp.449-456. https://doi.org/10.4334/JKCI.2014.26.4.449
  5. Alvarez-Ayuso, E., Querol, X., Plana, F., Alastuey, A., Moreno, N., Izquierdo, M., Font, O., Moreno, T., Diez, S., Vazquez, E., and Barra, M.,"Environmental, physical and structural characterisation of geopolymer matrixes synthesised from coal (co-)combustion fly ashes", Journal of Hazardous Materials, Vol.15, No.1-3, 2008, pp.175-183.
  6. Chindaprasirt P., Jaturapitakkul C., Chalee, W., and Rattanasak, U., "Comparative study on the characteristics of fly ash and bottom ash geopolymers", Waste Management, Vol.29, 2009, pp.539-543. https://doi.org/10.1016/j.wasman.2008.06.023
  7. Chang, J. J., Yeih, W., and Hung, C. C., "Effects of gypsum and phosphoric acid on the properties of sodium silicate-based alkali-activated slag pastes", Cement and Concrete Composites, Vol.27, No.27, 2005, pp.85-91. https://doi.org/10.1016/j.cemconcomp.2003.12.001
  8. Gorhan, G. and Kurklu, G., "The influence of the NaOH solutionon the properties of the fly ash-based geopolymer mortar cured at different temperatures", Composites Part B: Engineering, Vol.58, 2014, pp.371-377. https://doi.org/10.1016/j.compositesb.2013.10.082
  9. Fernandez-Jimenez, A. M., Palomo, A., and Lopez-Hombrados, C., "Engineering properties of alkali-activated fly ash concrete", ACI Materials Journal, Vol.103, No.2, 2006, pp.106-112.
  10. Garcia, E., Campos-Venegas, K., Gorokhovsky, A., and Fernandez, A., "Cementitious composites of pulverized fuel ash and blast furnace slag activated by sodium silicate: effect of $Na_2O$ concentration and modulus", Advances in Applied Ceramics, Vol.105, No.4, 2006, pp.201-208. https://doi.org/10.1179/174367606X120151
  11. Pu, X. C., Gan, C. C., Wang, S. D., and Yang, C. H., "Summary reports of research on alkali-activated slag cement and concrete", Chongqing Institute of Architecture and Engineering, Vols.1-6, 1988.
  12. Poon, C. S., Kou, S. C., Lam, L., and Lin, Z. S., "Activation of fly ash/cement systems using calcium sulfate anhydrite ($CaSO_4$)", Cement and Concrete Research, Vol.31, No.6, 2001, pp.873-881. https://doi.org/10.1016/S0008-8846(01)00478-1
  13. Xu, A. and Sarkar, S. L., "Microstructural study of gypsum activated fly ash hydration in cement paste", Cement and Concrete Research, Vol.21, 1991, pp.1137-1147. https://doi.org/10.1016/0008-8846(91)90074-R
  14. Shi, C. J., "Early microstructure development of activated lime-fly ash pastes", Cement and Concrete Research, Vol.26, No.9, 1996, pp.1351-1359. https://doi.org/10.1016/0008-8846(96)00123-8
  15. Kim, M. S., Jun, Y., Lee, C., and Oh, J. E., "Use of CaO as an activator for producing a price-competitive non-cement structural binder using ground granulated blast furnace slag", Cement and Concrete Research, Vol.54, 2013, pp. 208-214. https://doi.org/10.1016/j.cemconres.2013.09.011
  16. Boonserm, K., Sata, V., Pimraksa, K., and Chindaprasirt, P., "Microstructure and strength of blended FBC-PCC fly ash geopolymer containing gypsum as an additive", ScienceAsia, Vol.38, 2012, pp.175-181. https://doi.org/10.2306/scienceasia1513-1874.2012.38.175
  17. Rattanasak, U., Pankhet, K., and Chindaprasirt, P., "Effect of chemical admixtures on properties of high-calcium fly ash geopolymer", International Journal of Minerals, Metallurgy, and Materials, Vol.18, No.3, 2011, pp.364-369. https://doi.org/10.1007/s12613-011-0448-3
  18. Pimraksa, K. and Chindaprasirt, P., "Lightweight bricks made of diatomaceous earth, lime and gypsum", CeramicsI nternational, Vol.35, No.1, 2009, pp.471-478.
  19. Skvara, F., Kopecky, L., Smilauer, V., and Bittnar, Z., "Material and structural characterization of alkali activated low-calcium brown coal fly ash", Journal of Hazardous Materials, Vol.168, No.2-3, 2009, pp.711-720. https://doi.org/10.1016/j.jhazmat.2009.02.089
  20. Mehta, P. K., and Monteiro, P. J. M., Concrete: microstructure, properties, and materials: McGraw-Hill New York, 2006.
  21. Zhang, L., Ahmari, S., and Zhang, J., "Synthesis and characterization of fly ash modified mine tailings-based geopolymers", Construction and Building Materials, Vol.25, 2011, pp.3773-3781. https://doi.org/10.1016/j.conbuildmat.2011.04.005
  22. De Silva, P., Sagoe-Crenstil, K., and Sirivivatnanon, V., "Kinetics of geopolymerization: Role of $Al_2O_3$ and $SiO_2$", Cement and Concrete Research, Vol.37, 2007, pp.512-518. https://doi.org/10.1016/j.cemconres.2007.01.003
  23. Oh, J. E., Moon, J., Oh, S. G., Clark, S. M., and Monteiro, P. J. M., "Microstructural and compositional change of NaOHactivated high calcium fly ash by incorporating Na-aluminate and co-existence of geopolymeric gel and C-S-H(I)", Cement and Concrete Research, Vol.42, 2012, pp.673-685. https://doi.org/10.1016/j.cemconres.2012.02.002
  24. Jun, Y. and Oh, J. E., "Mechanical and microstructural dissimilarities in alkali-activation for six Class F Korean fly ashes", Construction and Building Materials, Vol.52, 2014, pp.396-403. https://doi.org/10.1016/j.conbuildmat.2013.11.058
  25. Boonserm, K., Sata, V., Pimraksa, K., and Chindaprasirt, P., "Impoved geopolymerization of bottom ash by incorporating fly ash and using waste gypsum as additive", Cement & Concrete Composites, Vol.34, 2012, pp.819-824. https://doi.org/10.1016/j.cemconcomp.2012.04.001