Design and characterization of Cameroonian pegmatite-calcined clay binary mortars via geopolymerisation

In this work, geopolymer binders obtained from a mixture of Cameroonian pegmatite and type 1/ 1 calcined clays (metakaolin and metahalloysite) at different proportions (10-30 wt%) were used for the formulation of mortars. The kinetic parameters of the reactivity of the pegmatite mixed with different calcined clays in an alkaline medium were evaluated via the heat of reaction data measured at an isothermal conduction calorimeter (ICC) at 27 degrees C for the first 24 h. As feedstock precursors, the different products obtained were characterized by means of mechanical flexural and compressive resistances (dry and wet), physical properties, Fourier Transform infrared spectroscopy and Scanning Electron Microscope. The results showed that the compressive strength values vary with the type and percentage of calcined clays. The highest values were achieved with mortars containing 30 wt% of the different calcined clays, ranging from approximately 25-35 MPa in dry conditions. The flexural strength values of the mortars increase also with the incorporation of calcined clay and vary from 1.0 to 4.5 MPa. After 72 h of immersion of these samples in water, they lost less than 60% of their mechanical performance. The water absorption rate of the mortars decreases with the incorporation of calcined clays and ranges from 7.5 to 13.8%. FT-IR indicated the reactivity of pegmatite during the geopolymerisation process while SEM micrographs exhibited a better cohesion between the aggregates (river sand, 200 & mu;m & LE; ɸ & LE; 2000 & mu;m) and the binder. The above-mentioned pegmatite-calcined clay mortars appear to be a suitable candidate for engineering applications (civil engineering)

Particles size and distribution on the improvement of the mechanical performance of high strength solid solution based inorganic polymer composites: A microstructural approach

This research reports on the influence of particle size and distribution on the physical, mechanical and microstructural features of solid solutions (feldspathic materials) based inorganic polymer composites (IPCs). Both granite and pegmatite were ground to different degree of finess making four different granulometry with particles of 63, 80, 125 and 200 μm. The respective mixes receive 15 wt% of metakaolin and were activated with a well designed alkaline solution. Matrices obtained showed high compressive and flexural strengths in the range 101.2–131.3 MPa, and 29–35.5 MPa, respectively. It was observed that the optimum mechanical performance of these matrices can be achieved through a mix-design of different grades of granulometry. This was suggested by mechanism combining reactivity and particles packing. In fact, although it can be expected that the finess of the combination of the particles size under 63 μm might present the better reactivity, it is showing that the combination of fine, medium and coarse particles is efficient in achieving denser and tougher microstructure. Lower cumulative pore volume (17 mL g−1) of the composites based on pegmatite, value not far from that of natural stones, resulted in a higher impact resistance of 3.03 J. It was concluded that designing the feldspathic rock-based composites with high strengths appear as sustainable, low energy consumption and environmentally-friendly materials for the structural construction