Effect of sulfates on the physical properties of Portland cement mortars

Abstract

Concrete is produced by mixing cement, aggregate and water. The aggregates are inert materials and the chemical reactions take place between cement and water. Therefore, the properties of mixing water are very important for the behavior of fresh and hardened concrete. Practically, the water used for drinking is suitable for the concrete production. In any case, the mixing water which is planned to be used in concrete should be tested since the presence of impurities affects significantly the properties of the concrete. In this investigation, magnesium sulfate, sodium sulfate and sodium sulfide were used in various proportions for the preparation of salty solutions. Portland cement pastes and mortars were produced by using these solutions as mixing water. The initial and final setting times of cement pastes, unit weights of fresh mortars and the drying shrinkage values of hardened mortar specimens were determined according to relevant standards. The results showed that the initial setting times accelerated and final setting times delayed generally by the addition of salts. There was no significant effect of mixing water on the unit weights of fresh mortars. It was also observed that the drying shrinkage values increased by magnesium and sodium sulfate and decreased by sodium sulfide.