Preparation and characterization of waterproof autoclaved aerated concrete using molybdenum tailings as the raw materials

As a kind of solid waste, molybdenum tailings are used to prepare low density autoclaved aerated concrete (AAC) (dry density & LE;450 kg m(-3)), which greatly improve their utilization rate and reduce stockpiling. Several studies showed that hydrophobic agents could further increase the performance of AAC by reducing the water absorption and improving the thermal insulation properties. The present study investigates the impact of different water-repellents such as powdered silane, zinc stearate, water dispersible zinc stearate, and osmotic crystalline on the compressive strength, thermal conductivity, and water absorption of AAC. The amount of waterrepellent to be added to the AAC samples is calculated by the mass of total siliceous and calcareous materials and the following concentrations of water-repellents are mixed with AAC: 0.05%, 0.1%, 0.15%, 0.2%, 0.25% and 0.3%. Spectroscopic and microscopic analyses revealed the content and morphology of the hydration products of AAC, and the changes in the pore structure. The obtained results clearly suggest that all the tested hydrophobic agents can reduce the water absorption and improve the compressive strength and the thermal insulation properties of AAC samples. Interestingly, powdered silane has the best effect when compared to other water repellents tested in this study. The improved performance of powdered silane is due to the formation of a hydrophobic film on the surface of the pore wall, which, in turn, increases the content of tobermorite crystals, and reduces the pore size of AAC samples.

Automated summary

Molybdenum tailings can be transformed into low density autoclaved aerated concrete (AAC) to improve utilization rate and reduce stockpiling. This study investigated the impact of different water-repellents on the compressive strength, thermal conductivity, and water absorption of AAC. Results showed that all tested hydrophobic agents can reduce water absorption and improve the properties of AAC, with powdered silane having the best effect.