The impact of the curing process on the efflorescence and mechanical properties of basalt fibre reinforced fly ash-based geopolymer composites

¹ Cracow University of Technology, Institute of Material Engineering, Faculty of Material Engineering and Physics,, Warszawska 24, 31-155, Cracow, Poland
² University of Miskolc, Institute of Raw Material Preparation and Environmental Processing, 3515, Miskolc, Egyetemváros, Hungary
³ Technical University of Liberec, Faculty of Mechanical Engineering, Department of Material Science, Studentska 2, Liberec, 461 17, the Czech Republic
⁴ Reykjavik University, Civil Engineering, Menntavegur 1, IS-101, Reykjavik, Iceland

^* Corresponding author: dariusz.Mierzwiński@pk.edu.pl

Abstract

Efflorescence is one of the limitations of the widespread use of geopolymers. This problem is caused by excess unreacted sodium oxide remaining inside materials. Unreacted sodium oxide creates white efflorescence on the surface of the produced material in the form of sodium carbonate heptahydrate Na₂CO₃∙ 7H₂O. It decreases not only the aesthetic value of the final products, but also the mechanical properties of the material. The aim of this article is to analyse the influence of the curing method on the appearance of efflorescence on geopolymer composites reinforced by short basalt, especially on mechanical properties. Class F fly ash from the ‘Skawina’ coal-fired power plant (located in Skawina, Lesser Poland, Poland) was used as raw material for the geopolymerization process. The article compares two methods of curing: typical laboratory conditions (in the air) and samples submerged in water. Three series of fly ash-based geopolymer were cast: basalt fibres were added as 1% and 2% by weight of fly ash and one control series without any fibres. The investigation was performed using visual analysis, including microstructure investigation, and the testing of mechanical properties (compressive strength at ambient temperature) after 28 days.