Effects of sulfates on strength of Portland cement mortars

Abstract

Concrete is a composite material which is produced by mixing cement, aggregate, water and if required admixtures. The quality of mixing water plays an important role in the mechanical behavior of hardened mortar and concrete. Presence of some impurities in mixing water may influence the chemical reactions between water and cement and affects the strength of hardened material. In this experimental study, Portland cement mortar specimens were produced by using mixing water including different amounts of magnesium and sodium sulfate. Test specimens were prepared with water cement ratio of 0.6. Totally, nine types of mixing water were prepared with four different amounts of two different salts and tap water. The specimens were subjected to flexural and compressive strength tests at the ages of 7, 28 and 90 days and the effects of sulfate salts present in mixing water on the strength of hardened mortars were extensively analyzed. The results showed that the effect of magnesium sulfate was more pronounced when the concentration of the salt exceeds 6 percent. The strength of mortars decreased as the concentration of the sodium sulfate increased.