Microstructure and Carbonation Resistance of Gypsum-Added Autoclaved Aerated Concrete

Abstract

Calcium sulfate is often used as a raw material for Autoclaved Aerated Concrete (AAC) to improve several properties. Microstructure and carbonation resistance of gypsum (CaSO4·2H₂O) added AAC were investigated. Anhydrite (CaSO₄) and hemihydrate (CaSO₄·0.5H₂O) recrystallized after autoclaving and filled the finer pores, while the total pore volume was unchanged. Fractal dimension obtained from the water vapor sorption isotherms data increased and Knudsen diffusion coefficient of carbon dioxide gas decreased with the increase of the gypsum content. Carbonation resistance was improved with increase in the gypsum content from 0 to 15 mass%. The mechanism of the increase of the carbonation resistance of the gypsum-added AAC is attributed to the decrease of the Knudsen diffusion coefficient associated with an increase in the fractal dimension of the liquid and gas interface.