Alkali Activation of Milled Red Brick Waste and Calcined Illite Clay with Silica Gel Addition

The role of precursor characteristics and mixture composition design of alkali-activated materials (AAM) has been intensively researched with different types of alumino-silicate sources. Two illite-based precursors were prepared and investigated—(i) raw illite clay (IC) treated in a laboratory at 700, 750, and 800 ∘C and (ii) a red brick waste coming from the brick production plant. The fineness of precursors was determined and compared. The precursors were activated with 6 M and 7 M NaOH alkali solutions. Silica gel addition was considered in the composition of AAM. The XRD results indicate the transformation of both precursor types under alkali activation. The efflorescence salts were analyzed on the samples with silica gel addition. Calcined IC precursor allowed us to obtain AAM with a strength from 11 to 16 MPa with an increasing strength gain during curing. The red brick waste precursor showed a compressive strength from 14 to 28 MPa. A high early strength was obtained with no further strength increase. The hydrosodalite and zeolite crystals were detected in the structure of AAM based on the red brick waste precursor. The results indicate different characteristics of AAM based on similar source precursors, showing the important role of the proper treatment of precursors before alkali activation