Title: Sulfate Resistance of Portland and Slag Cement Concretes Exposed to Sodium Sulfate for 38 Years
Author(s): Fatemeh Alapour and R. Douglas Hooton
Publication: Materials Journal
Appears on pages(s): 477-490
Keywords: concrete durability; ettringite; slag; sulfate attack
In 1976, production of separately ground, pelletized blast-furnace slag started near Hamilton, ON, Canada, and a research program began in 1977 to study the effects of this slag cement on sulfate resistance of concrete. For this purpose, concrete cylinders were cast from eight batches using normal, moderate sulfateresistant and highly sulfate-resistant portland cement types as well as mixtures of high-C3A portland cement plus slag at a watercementitious materials ratio (w/cm) of 0.45 or 0.50. In the present study, samples were cut from concrete cylinders after 38 years of exposure to sodium sulfate solutions and thin sections were prepared for analysis using scanning electron microscopy. Microstructural details were investigated from the exposed surface to the center of each cylinder, and different phases were determined. Ettringite, thaumasite, gypsum, and layers of calcium carbonate were found to have formed in the samples. A 65% slag substitution of high-C3A portland cement was very effective in improving the performance of concrete exposed to sodium sulfate.