Abstract
Metakaolinite-based geopolymer binder was prepared at room temperature by mixing calcined claystone and potassium alkaline activator. Various granular inorganic fillers were added, amounting to 65 vol % to form geopolymer composites. The effect of four types of fillers (sand quartz, chamotte, cordierite, and corundum) on the thermo-mechanical properties of metakaolinite-based geopolymer composites were investigated. The samples were also examined by an X-ray diffraction method to determine their phase composition. The pore size distributions were determined by a mercury intrusion porosimeter. The XRD revealed the crystallization of new phase (leucite) after thermal exposure at 1000 °C and higher. Geopolymer binders had low mechanical properties (flexural strength 2.5 MPa and compressive strength 45 MPa) and poor thermo-mechanical properties (especially high shrinkage—total shrinkage 9%) compared to geopolymer composites (flexural strength up to 13.8 MPa, compressive strength up to 95 MPa and total shrinkage up to 1%). The addition of fillers reduced the shrinkage of geopolymers and improved their mechanical properties. The results have shown that the compressive strength tested in situ and after exposure to high temperature are in conflict. Geopolymer composites with the addition of chamotte had the best mechanical properties before and after thermal exposure (compressive strength up to 95 MPa). The average pore size diameters increased with the increasing temperature (from 10 nm to approx. 700 nm). The fillers addition decreased the pore volume (from 250 mm3/g to approx. 100 mm3/g).
Highlights
Alkali activated aluminosilicates, such as inorganic geopolymers, have been attracting attention in the last few years as a new material with a wide variety of application and excellent properties [1,2].Good mechanical properties, such as resistance to high temperatures and chemicals, are the main attributes of geopolymers [3,4,5]
Raw materials used for the preparation of geopolymer binder were all commercially available products: a metakaolinite-rich material Mefisto L05 produced by the calcination of kaolinitic claystone at about 750 ◦ C in a rotary kiln (České lupkové závody, a.s., Nové Strašecí, Czech Republic), potassium silicate (Vodní sklo, a.s., Prague, Czech Republic) and potassium hydroxide pellets
Leucite was observed in geopolymer binder prepared from metakaolin and potassium alkaline activator after heat exposure at 800 ◦ C [38], 1000 ◦ C [34,39], 1050 ◦ C [40], and 1300 ◦ C [11]
Summary
Alkali activated aluminosilicates, such as inorganic geopolymers, have been attracting attention in the last few years as a new material with a wide variety of application and excellent properties [1,2]. Good mechanical properties, such as resistance to high temperatures and chemicals (especially acids and organic solvents), are the main attributes of geopolymers [3,4,5]. Geopolymer binders are formed by mixing powdered aluminosilicates with a liquid alkaline activator. A liquid alkali silicate (water glass) and alkali metal hydroxide solution are usually used as the alkaline activator. During the process of synthesis of geopolymers, the aluminosilicates are partially dissolved in an alkaline medium
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