Influence of the Kaolinite Calcination Conditions on the Compressive Strength of Geopolymer
Abstract
Among the cementitious materials, geopolymers not only attract interest due to the low emission of CO2 in their manufacturing process, but also because of their good mechanical and chemical properties, together with their resistance to fire. They can be made from different raw materials including various wastes from industrial activities and mineral extraction. In this study, metakaolin was obtained from kaolinite calcined under different conditions. In this case kaolinite is a by-product of sand extraction. It was observed that the calcination conditions (kiln heating rate, calcination time and temperature) had a strong influence on the compressive strength of geopolymer after 28 days of cure. They also affected the composition of the geopolymer, which was prepared by mixing metakaolin, alkaline sodium silicate and sodium hydroxide solution.Compressivestrengthsintherangefrom10MPato50MPamaybeobserved, depending on the combination of these factors. A factorial design of experiments allowed the isolation of the effect of each factor and its interactions, offering new insights into the complexity of the geopolymeric reactions and highlighting the need for a rigid control of the calcination conditions of kaolinite and the composition of the geopolymer samples to obtain the desired compressive strength.
Keywords: kaolinite, calcination, metakaolin, geopolymer, compressive strength.
References
[1] Boca Santa, R. A. A., Soares, C., and Riella, H. G. (2017). Geopolymer obtained from bottom ash as source of aluminosilicate cured at room temperature. Construction and Building Materials, vol. 157, pp. 459-466; Mikilčić, H., et al (2013). CO2emission reduction in the cement industry. CEt – Chemical Engineering Transactions, vol. 35, pp. 703-708.
[2] Sharma, R. (2017). Cement Industry Trends Report. (India: TERI), p.17.
[3] Davidovits, J. (2002). 30 years of successes and failures in geopolymer applications. Market trends and potential breakthroughs. Geopolymer 2002 Conference, October 28-29, Melbourne, Australia; Davidovits, J. (2005) Geopolymer chemistry and applications. 4th Edition. (Saint Quentin: Insitut Géopolumère), p. 644.
[4] Boca Santa, R. A. A., Soares, C., and Riella, H. G. (2017). Geopolymer obtained from bottom ash as source of aluminosilicate cured at room temperature. Construction and Building Materials, vol. 157, pp. 459-466; Turner, L. K. and Collins, F. G. (2013) Carbon dioxide equivalent (CO2-e) emissions: A comparison between geopolymer and OPC cement concrete. Construction and Building Materials, vol. 43, pp. 125-130.
[5] Ye, N. et al. (2014). Synthesis and characterization of geopolymer from Bayer red mud with thermal pretreatment. Journal of the American Ceramic Society, pp. 1652-1660.
[6] ABNT, 2007. NBR 5739 Concreto - Ensaio de compressão de corpos-de-prova cilindricos, Associação Brasileira de Normas Técnicas.