Characterization and mechanical properties of one-part geopolymer based on a pure metakaolin

Abstract

Geopolymers are amorphous silicate polymers that have been extensively studied due to their applications, scientific and technical relevance, and their potential as cement in substitution to Portland. Much of the focus has been in the use of precursors and aggregates that are rarely pure and homogeneous with the use of tailings being very common. The presence of these impurities complicates the interpretation of some spectral methods, mainly infrared spectrometry. Therefore, this research focuses on the use of a nearly pure kaolin main precursor, having only a trace of iron and titanium, along with other almost pure reagents, to achieve an ideal geopolymer. It was possible to produce metakaolinite, resulting in a material with a good size particle (8.24µm) and surface specific area (6.57m 2 /g). The XRD result shows that the calcination process resulted in 100% of amorphous material. FTIR data revealed the presence of H 2 O and NaCO 3 in the geopolymer. More important, the Si-Al-O various bands located between 1100 and 500cm -1 validate the polymerization reaction effectiveness. SEM-EDS analyses have demonstrated that the reaction with Na 2 SiO 3 and NaOH were nearly complete, concerning the finer metakaolinite particles that comprised the material's matrix. However, the coarser metakaolinite lamellae, in the 15-35µm range, did not react completely; a thin border layer was enriched with sodium and most of the interior material maintained its Si-Al-O composition. The presence of traces of iron and titanium did not influence in the polymerization reaction. Compressive strength values of the geopolymer have presented good values in the range of 25 to 35 MPa.