High strength metahalloysite based geopolymer

The unique properties of aluminosilicates had made them valuable in the wide range of industrial applications. One branch of application represents building materials. A significant factor of the level of the quality of engineering properties of building materials anyhow is the water/binder ratio. It is well known that its decreasing value effectively increases strength and quality of other engineering properties of the material. Due to the accompanying effect impairing workability of the mixture for processing the pressure compaction is needed. The subject of the paper are the results of the study of the properties of metahalloysite based geopolymer prepared under the use of the combination of very low water/metahalloysite ratio (0.08), pressure compaction of the fresh mixture by applying an uniaxial compressive stress of 300 MPa and alkali activation. The effect of preparation conditions was systematically studied by thermal analysis (DTA, GTA), mercury intrusion porosimetry, scanning microscopy and compressive strength estimation of the geopolymer. The used metahalloysite was a product of calcination of the source material at 650 degrees C 4 h. It was an amorphous material showing an increased thermodynamic unstability and herewith an increased reactivity in comparison with the unheated solid. The metahalloysite based geopolymer pressure compacted paste reached after 24 h of the hardening compressive strength of 76.2 MPa whereas the reference paste only 0.03 MPa. It represents 2540 times increase in behalf of the pressure compacted paste. High compressive strength was evidently the consequence of the found high homogeneous and dense pore structure of the pressure compacted paste. The regression analysis shown for the geopolymer binder systems a polynomial empirical equations as an appropriate configuration. For the alkali activated slag and Portland cement systems the exponential configuration was suitable. The cause of the difference may be apparent phase composition. It was pronouncedly amorphous structure of the geopolymer binder systems opposite to the combined amorphous and crystalline structures distinctive for alkali-activated slag and Portland cement binder systems. Then the resulted different destruction mechanism under the loading, at the strength test of the material. For the elucidation of the causality more detailed research is needed. (C) 2013 Elsevier Ltd. All rights reserved.