The effect of mineralogy of calcined shales on the alkali activation and geopolymerization reactions: A case study from Abu-Tartur plateau, Western Desert, Egypt

The effect of mineralogy of calcined shales on the alkali activation and geopolymerization reactions was studied. Shales under study included black and Dakhla shales, which were obtained from the Abu-Tartur plateau in the Western Desert of Egypt and characterized using optical microscope, SEM, XRF, XRD, and FTIR. The dehydroxylation of shale samples was performed at 550, 650, 750, and 850 °C for one hour. The mineral transformations on calcination were monitored using SEM, XRD and FTIR. The alkali activation process was then conducted on the calcined samples using a mixture of sodium hydroxide and sodium silicate at 1.2 solid/liquid mass ratio. The resultant pasts were molded in steel cubes (50 × 50 × 50mm in diameter) and cured at 70 °C for 48 h. The compressive strength of cured samples was measured to reveal the extent to which the dehydroxylation achieved. The maximum strength values were reported at 4.19 MPa and 2.49 MPa for the calcined black shale and Dakhla shale, respectively. By comparing with literature, the present strength is considered to be too much low. This indicates a deficiency of the dehydroxylation of clay minerals, a little amount of the active amorphous phases, and the dominance of low reactive crystalline phases through the whole range of calcination process.