Alkali-Activated Material Based on Red Clay and Silica Gel Waste

Industrial by-products such as silica gel waste and red clay based on natural illite, have been used as precursors for the preparation of alkali activated materials (AAM). Raw materials, precursors and the alkali-activated materials were examined using X-ray diffraction, XRFA and SEM analysis. The reactive concentrations of Si and Al were determined using the colorimetric method. The compressive strength of alkali-activated samples was also evaluated. The precursors were made from Lithuanian red clay (Ukmergė deposit) and silica gel waste. The clay and silica gel waste were first mixed together and then calcined at 900 °C or 600 °C to obtain the precursors. The results show that during the calcination process, new phase CaF 2 formed in the precursors. It is possible that fluoride compound which forms during the calcination process, acts as a flux (at a temperature of 900 °C), and for this reason, the reactive amorphous phase is transformed into mullite and cristobalite (crystalline phases), which are not reactive. According to the XRD diffractogram, calcination at a temperature of 600 °C was sufficient to convert the crystalline structure of kaolinite into an amorphous phase. In this case, at a calcination temperature of 600 °C, it was recommended to use up to 25% of silica gel waste. The maximal compressive strength (7 MPa) was achieved by using 5% of silicagel waste. It was concluded that red clay–silica gel waste AAM can be considered for the production of green composite materials.