Reaction kinetics and microstructure of pegmatite-based geopolymer composites: influence of calcined clay nature

This research reports the investigations of threshold reactivity limit of blends
of pegmatite with different calcined clays as well as the influence of calcined
clay source on the geopolymerization kinetic, microstructural, and physicomechanical
properties of feldspathic mineral-based inorganic polymer composites.
These composites were designed from 85 to 94 wt% of the solid solution of
pegmatite and calcined clay. The three-point flexural and compressive strengths,
porosity, and microstructure as well as heat evolution rate of geopolymerization
reactions of resulting composites were affected by the type of calcined clay. The
four calcined clays provided the highest mechanical properties of the composites
when added in the range of 12–15 wt%. Specifically, the values of flexural
and compressive strengths ranged from 32 to 34 MPa and 101 to 105 MPa, respectively,
for geopolymer composites with 15 wt% of metakolin added, while they
ranged from 38 to 42 MPa and 106 to 107 MPa with 12 wt% of meta-hallosyte
added. The polycondensation/polymerization process of calcined clay developed
sufficient amounts of N-A-S-H and polysialate geopolymer to cover the
incongruently dissolved fine particles of pegmatite. The resulting microstructure
was dense and compact with the lower cumulative pore volume at about 91
mm3/g. It was concluded that designing the pegmatite/clay-based geopolymer
composites with high mechanical strengths and low porosity resulted in sustainable,
low energy consumption and environmental-friendly materials for civil
engineering.
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