Structure and properties of new eco-material obtained by phosphoric acid attack of natural Tunisian clay

In this work, new three dimensional geopolymer materials based on dehydroxylated natural kaolin and phosphoric acid were synthesized. The effects of Si/P molar ratio and curing time were studied. The structures of raw, calcined kaolin and geopolymers synthesized were investigated using X-ray diffraction analysis, IR spectroscopy, scanning electronic microscope, 31(P), Si-29 and Al-27 MAS-NMR and by mechanical measurements. The mechanical strength of geopolymers is maximum when Si/P molar ratio, equal to 2.25, which corresponds to Al/P ratio = 1. The mechanical properties are correlated with the amount of amorphous phase in geopolymer which is determined by the Rietveld method. In addition to metakaolin, illite mineral contributes to geopolymerization. (C) 2014 Elsevier B.V. All rights reserved.