Efflorescence in red-clay ceramics: methodology to evaluate its intensity and migration SO4 -2 and Ca+2 ions

Abstract

This study investigates the migration of SO₄^–2 and Ca⁺² ions in a red-clay ceramic, simulating the process of efflorescence. Ceramic bodies were molded (70x27x9 mm³) by vacuum extrusion formulated with different contents of CaSO₄.2H₂O (0%, 4%, 8%, and 16% in weight) and burnt at different temperatures (800 °C, 850 °C, 900 °C, 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 ASTMC67/2003 Standard and by testing the solubilization of SO₄^–2 and Ca⁺² ions after 1 h with the ceramic bodies immersed in hot water as well as after 7, 14 and 28 consecutive days immersion in cold water. In the quantification of efflorescence, a new image analysis methodology was developed by using the graphic software Image Tools 3.0. The results allowed in establishing a relationship between the efflorescence of the investigated ions, physical properties (water absorption and apparent porosity), pore size distribution and solubilization.