Abstract
A metakaolinite-based geopolymer binder was prepared by using calcined claystone as the main raw material and potassium as the alkaline activator. Chamotte was added (65 vol%) to form geopolymer composites. Potassium hydroxide (KOH) was used to adjust the molar ratio of K/Al and the effect of K/Al on thermo-mechanical properties of geopolymer composites was investigated. This study aimed to analyze the effect of K/Al ratio and exposure to high temperatures (up to 1200 °C) on the compressive and flexural strengths, phase composition, pore size distribution, and thermal dilatation. With an increasing K/Al ratio, the crystallization temperature of the new phases (leucite and kalsilite) decreased. Increasing content of K/Al led to a decline in the onset temperature of the major shrinkage. The average pore size slightly increased with increasing K/Al ratio at laboratory temperature. Mechanical properties of geopolymer composites showed degradation with the increase of the K/Al ratio. The exception was the local maximum at a K/Al ratio equal to one. The results showed that the compressive strength decreases with increasing temperature. For thermal applications above 600 °C, it is better to use samples with lower K/Al ratios (0.55 or 0.70).
Highlights
Geopolymers are inorganic materials with a wide variety of applications and superior properties which have been intensively studied over the past five decades [1,2,3]
Starting materials used for the preparation of geopolymer binders were commercial metakaolinite-rich material Mefisto L05 produced by the calcination of kaolinitic claystone at about 750 ◦C in a rotary kiln (Ceské lupkové závody, a.s., Nové Strašecí, Czech Republic), potassium silicate and potassium hydroxide pellets (G.R. grade, 88.2 wt% KOH, Lach-Ner, s.r.o., Neratovice, Czech Republic)
Leucite and kalsilite are common crystalline phases for potassium geopolymer binders formed after heat exposure at temperatures ranging from 800 ◦C to 1300 ◦C [36,38,39,40,41]
Summary
Geopolymers are inorganic materials with a wide variety of applications and superior properties which have been intensively studied over the past five decades [1,2,3]. Numerous applications of geopolymers have been developed based on their properties—building materials [7], coatings [8], catalysts [9], fiber composites [10,11], sorbents [12], materials for 3D printing [13], waste immobilization [14], etc. Geopolymers are synthesized by mixing powdered aluminosilicates with a liquid alkaline activator at a laboratory (LT) or slightly higher temperatures. The process of geopolymer synthesis involves partial dissolution of solid material rich in Al and Si in an alkaline medium, followed by polycondensation reactions of hydrolyzed silicates and aluminates into a three-dimensional polymer network [20,21]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
