Evaluation of Concretes Exposed to Sulfate Solutions for 38 Years

In 1975, a separately ground blast furnace slag was developed in Hamilton, Ontario, and a research program was begun in 1977 to study the effects of this slag on sulfate resistance of concrete. Concrete cylinders were cast from 8 batches using Portland cement types GU, MS, HS, and mixtures of GU plus slag at w/cm of 0.45 or 0.50. In this study, cylinders were removed from the sulfate solutions and thin sections were prepared for SEM/EDS analysis. Microstructural details were investigated, and different phases were determined. Qualitative maps were also prepared using Micro-XRF. Ettringite, thaumasite, and gypsum as well as layers of brucite and/or calcium carbonate were found to have formed in the samples. A 65% slag substitution was the most effective in improving the performance of concrete exposed to sodium sulfate. However, the damage caused by magnesium sulfate was found to be more severe than by the sodium sulfate.M.A.S