The displacement of SO4(2-) and Ca2+ ions in a red-clay ceramic, simulating the process of efflorescence, was studied. Ceramic bodies were molded (70 × 27 × 9 mm³) by vacuum extrusion formulated with different contents of CaSO4.2H2O (0%, 2%, 4%, 8%, and 16% in weight) and fired at different temperatures (800, 850, 900, and 950 °C) for 12 h. Ceramic bodies were characterized in terms of water absorption, apparent porosity and pore size distribution. Efflorescence was evaluated according to the norms of ASTMC67/2003. The solubilization of SO4(2-) and Ca2+ ions was tested after 1 h with the ceramic bodies immersed in hot water as well as after 7, 14 and 28 consecutive days with the ceramic bodies immersed in cold water. Electrical conductivity tests were also carried out in the solubilized material from ceramic bodies 1 h and 7 days after the beginning of the assay, where the potential of these ions in the formation of efflorescence as a function of temperature was evaluated. In the quantification of efflorescence, a new image analysis methodology was developed. The results allowed establishing a relationship between the efflorescence of the investigated ions, physical properties (water absorption and apparent porosity), pore size distribution, solubilization and electrical conductivity.
efflorescence; calcium sulfate; ceramic materials; porosity
