Sulfate and Freeze-Thaw Resistance of Porous Geopolymer Based on Waste Clay and Aluminum Salt Slag

The search for efficient waste source precursors for geopolymer production is active in scientific society. The feasibility of using calcined kaolin clay and fly ash as suitable precursors for the production of geopolymers is widely described and acknowledged. The availability and energy input required to produce such precursors hinders their competing with traditional binders, however. Therefore, new by-product source precursors are sought in different industries. In this research, three industrial origin secondary raw materials are examined as precursors for the production of porous geopolymers. Calcined illite or kaolin clay in combination with salt cake from the aluminium scrap recycling industry after alkali activation gives lightweight material from 540-675 kg/m(3). A comparison of the two precursors was made, and the physical and mechanical properties were determined. Freeze-thaw resistance and sulfate attack were used to characterize durability. Results indicate the role of waste clay type and salt cake content on geopolymer properties as materials with similar appearance performed differently. The results show that metakaolin based geopolymers outperformed red clay based geopolymers and they can withstand from 25 to 50 freeze-thaw cycles with strength loss from 10 to 65%. Sulfate attack showed significant strength loss for red clay based geopolymers after 61 days of soaking time in contrast to metakaolin based geopolymers.