2021 Volume 129 Issue 5 Pages 261-266
The dissolution behavior of calcium aluminosilicate (CAS) glasses with various CaO and Al2O3 concentrations was investigated at 180 °C in NaOH aqueous solutions with an initial pH of 13.2–14.0. A CaO–Na2O–Al2O3–SiO2–H2O (C–N–A–S–H) layer was formed on the immersed glass surface due to the dissolution and penetration of the glass and solution constituents. An excellent alkali durability was achieved by the minimization of Al2O3 addition and a [CaO]/[SiO2] molar ratio of 1.10–1.20 for the glass composition design. The results of the infrared spectroscopy indicated that the C–N–A–S–H layer contained H2O and CO32− species from the ambient atmosphere and consisted of the network structure of SiO4–AlO4 tetrahedra. The hydrothermal reactions between the CAS glasses and NaOH solution promoted the formation of the C–N–A–S–H layer and precipitation of Ca(OH)2 with an immersion time. Stable Al-substituted tobermorite and hillebrandite phases were finally formed on the immersed glass surfaces due to the hydrothermal reactions.