Effect of Sodium Aluminate on Compressive Strength of Geopolymer at Elevated Temperatures
Geopolymer is an inorganic material synthesized by alkali activation of source materials rich in soluble SiO2 and Al2O3. Many researches have studied the effect of aluminum species on the synthesis of geopolymer. However, it is still unclear about the influence of Al additives on the properties of geopolymer. The current study identified the role of the Al additive on the thermal performance of fly ash based geopolymer and observing the microstructure development of the composite. NaOH pellets were dissolved in water for 14 M (14 moles/L) sodium hydroxide solution which was used as an alkali activator. The weight ratio of alkali activator to fly ash was 0.40. Sodium aluminate powder was employed as an Al additive and added in amounts of 0.5 wt.% to 2 wt.% by the weight of fly ash. The mixture of alkali activator and fly ash was cured in a 75°C dry oven for 24 hours. Then, the hardened geopolymer samples were exposed to 300°C, 600°C and 900°C for 2 hours, respectively. The initial compressive strength after oven curing increased with increasing sodium aluminate content. It was also observed in SEM results that more amounts of geopolymer composite were synthesized as sodium aluminate was added. The compressive strength increased with increasing heating temperature from 300°C to 600°C regardless of sodium aluminate addition. It was consistent with the ATR-FTIR results that the peak position related to asymmetric stretching vibrations of Si-O-T (T: Si or Al) shifted to higher wavenumber as the heating temperature increased, indicating the further geopolymer reaction. In addition, geopolymer sample with higher content of sodium aluminate showed better compressive strength. It was also reflected on the IR results by more shift of the peak position assigned to Si-O-T toward the higher wavenumber. However, the compressive strength decreased after being exposed to 900°C in all samples. The degree of reduction in compressive strength was decreased with increasing sodium aluminate content. The deterioration in compressive strength was most severe in the geopolymer sample without sodium aluminate additive, while the samples with sodium aluminate addition showed better thermal durability at 900°C. This is related to the phase transformation with the occurrence of nepheline phase at 900°C, which was most predominant in the sample without sodium aluminate. In this work, it was concluded that sodium aluminate could be a good additive in the geopolymer synthesis by showing the improved compressive strength at elevated temperatures.
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 M. Rubenstein, "Emissions from the Cement Industry", Earth Institute of Columbia University, USA, 2012.
 S. Mindess, J. Francis Young, and David Darwin, Concrete, 2nd ed., Upper Saddle River, NJ, Pearson Education, 2002.
 J. Davidovits, "Global warming impact on the cement and aggregates industries", World Resource Review, vol. 6, pp. 263-278, 1994.
 J.S. Damtoft, J. Lukasik, D. Herfort, D. Sorrentino, and E.M. Gartner, “Sustainable development and climate change initiatives”, Cem. Concr. Res., vol. 38, pp. 115-127, 2007.
 K. Humphreys and M. Mahasenan, Toward a sustainable cement industry. Sub-study 8: climate change, An Independent Study Commissioned to Battelle by World Business Council for Sustainable Development, 2002.
 J.G.J. Oliver, G. Janssens-Maenhout, M. Muntean, and J.A.H.W. Peters, Trends in global CO2 emissions: 2015 report, PBL Netherlands Environmental Assessment Agency, The Hague, Report Number 1803, 2015.
 R. A. Fletcher, K. J. D. MacKenzie, Catherine L. Nicholson, Shiro Shimada, “The composition of range of aluminosilicate geopolymers”, J. Eur. Ceram. Soc., vol. 25, pp. 1471-1477, 2005.
 J. A. Tossell, “A theoretical study of the molecular basis of the Al avoidance rule and of the spectral characteristics of Al-O-Al linkages”, Am. Mineral., vol. 78, pp. 911-920, 1993.
 Maricela Lizcano, Andres Gonzalez, Sandip Basu, Karen Lozano, Miladin Radovic, “Effects of Water Content and Chemical Composition on Structural Properties of Alkaline Activated Metakaolin-Based Geopolymers”, J. Am. Ceram. Soc., vol. 95, pp. 2169-2177, 2012.
 C. A. Rees, John L. Provis, Grant C. Lukey, Jannie S.J. van Deventer, “In situ ATR-FTIR study of the early stages of fly ash geopolymer gel formation”, Langmuir, vol. 23, pp. 9076-9082, 2008.
 J. F. Stebbins, P. F. McMillan, D. B. Dingwell, Structure, Dynamics and Properties of Silicate Melts, Washington, D.C., Mineralogical Society of America, 1995.
 J. Davidovits, “Geopolymer chemistry and applications” (4th ed.), Geopolymer Institute, France, 2015.
 Luqian Weng, Kwesi Sagoe-Crentsil, Trevor Brown, Shenhua Song, “Effects of aluminates on the formation of geopolymers”, Mater. Sci. Eng. B, vol. 117, pp. 163-168, 2005.
 A. Hajimohammadi, John L. Provis, J. S. J van Deventer, “Effect of Alumina Release Rate on the Mechanism of Geopolymer Gel Formation”, Chem. Mater., vol. 22, pp. 5199-5208, 2010.
 A. Fernandez-Jimenez, A. Palomo, I. Sobrados, J. Sanz, “The role played by the reactive alumina content in the alkaline activation of fly ashes”, Microporous Mesoporous Mater., vol. 91, pp. 111-119, 2006.
 C. A. Rees, John L. Provis, Grant C. Lukey, Jannie S.J. van Deventer, “The mechanism of geopolymer gel formation investigated through seeded nucleation”, Colloids. Surf. A, vol. 318, pp. 97-105, 2008.
 D. J. Schipper, T. W. Lathouwers, C. Z. van Doorn, “Thermal Decomposition of Sodalites”, Philips Research Laboratories, Eindhoven, Netherlands.
 J. G. S van Jaarsveld, J. S. J. van Deventer, “Effect of the Alkali Metal Activator on the Properties of Fly Ash-Based Geopolymers”, Ind. Eng. Chem. Res., vo,. 38, pp. 3932-3941, 1999.
 Sateesh Babu Madavarapu, “FTIR Analysis of Alkali Activated Slag and Fly ash Using Deconvolution Techniques” M. D. Thesis, Arizona State University, U. S., 2014.
 Dimitrios Panias, Ioanna P. Giannopoulou, Theodora Perraki, “Effect of synthesis parameters on the mechanical properties of fly ash based geopolymers”, Colloids. Surf. A, vol. 301, pp. 246-254, 2007.
 Peter Duxson, Grant C. Lukey, Jannie S. J. van Deventer, “Evolution of Gel structure during Thermal Processing of Na-Geopolymer Gels”, Langmuir, vol. 22, pp. 8750-8757, 2006.