Influence of magnesium sulphate concentration on durability of concrete containing micro-silica, slag and limestone powder using durability index

• Durability of 36 concrete mix designs was investigated in three sulphate environments.
• Durability of the concretes was compared using a proposed durability index.
• Replacing 10% cement by micro-silica reduced the durability in magnesium sulphate.
• Replacing 15% cement by limestone powder increased the durability of concrete.
• The 5% magnesium sulphate solution was the most deteriorating environment.

Presented experimental study deals with the durability of concretes containing different additives of micro-silica, blast furnace slag and limestone powder as cement replacement with various ratios, exposed to magnesium sulphate environments with different concentrations of 5%, 10% and 14.7% (saturated concentration). Furthermore, the influence of different water-cement (w/c) ratios and also the parameter of time on reducing the compressive strength and increasing the volume of the concrete are investigated in the research process. To do so, 36 mix designs including concretes containing 0, 15 and 30% limestone powder as cement replacement in four conditions of cement replacement with 10% micro-silica, 10% blast furnace slag, 20% blast furnace slag and no cement replacement with slag or micro-silica were considered. Three w/c ratios of 0.3, 0.4 and 0.5 were considered and 864 concrete prisms with the size of 70 mm × 70 mm × 70 mm were produced. Compressive strength of the specimens at 140 and 280 days of sulphate exposure and also volume variations at 70, 140, 210 and 280 days of sulphate exposure were assessed to investigate the durability of different sulphate submerged concretes. In order to compare the durability of the concretes in each environment, a durability index was developed and the most durable concretes were introduced. The 5% magnesium sulphate solution was identified as the most destructive environment and concrete with w/c ratio of 0.3 containing 15% limestone powder and 20% slag was recognized as the most durable concrete.