Preparing autoclaved aerated concrete using molybdenum tailings

Abstract

Due to the background of the difficulty in molybdenum tailings disposal and the shortage of siliceous sand for autoclaved aerated concrete (AAC), molybdenum tailings were used for AAC production in this study. The main process parameters including the quicklime-cement ratio (Q/C), the molar calcium-silicon ratio (C/S), the water-solid materials ratio (W/S), the aluminum powder dosage, the autoclaved temperature, and the autoclaved time, on the basic physical and mechanical properties, such as slurry fluidity, foaming curves, dry density, and mechanical strength, were investigated. Moreover, the hydration production and microstructure were analyzed by XRD, thermal analysis, and SEM. The results showed that molybdenum tailings AAC (MAAC) with a dry density and compressive strength of 641.3 kg/m3 and 3.89 MPa, respectively, were successfully obtained under the following optimal conditions: molybdenum tailings, 60.13 %; quicklime 13.02 %; cement 26.03 %; gypsum 1 %; W/S 0.52; aluminum powder 0.07 %; autoclaved temperature 190 °C; autoclaved time 8h. The main mineral components of quartz and feldspar in the molybdenum tailings participated in the autoclaved reaction, while biotite did not. The main hydration products in the MAAC were flocculent C–S–H gel, plate-like, narrow plate-like, and grass-like tobermorite. The C–S–H gel and tobermorite bond each other and made the pore walls much denser, and were the main contributors to the MAAC strength.