Reaction Behavior of Autoclaved Aerated Concrete and Sodium Aluminate at Mild Alkaline and Acid Hydrothermal Conditions: Model for AAC Recycling

Abstract

Recyclable fractions such as calcium and sodium aluminosilicates including zeolite sodalite (SOD) were obtained from hydrothermal treatment of autoclaved aerated concrete (AAC) waste material under addition of sodium aluminate. Three experimental series were performed using hydrothermal conditions at temperatures of 80°C and 180°C (autogeneous pressure) and AAC aluminate mass ratios of 0.8 and 2.0. Different solvents were applied in each series; whereas the reactions were carried out in water or 1-molar NaOH, a special two-step process was developed, starting with acid leaching of AAC (1-molar citric acid), followed by alkaline treatment of the whole slurry in 1-molar NaOH. Final products were analyzed by X-ray powder diffraction. Selected samples were further investigated by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The results exhibit model character for new ways of resource recycling of AAC.