Effects of Crystalline Admixtures on Mechanical Properties and Durability of Concrete at Different Ambient Temperatures

Sodium sulfate, as a commonly used early strengthening agent, has been widely used in different areas.Because of its sulfonic acid group, sodium sulfate is also used as a cement capillary crystal waterproof material.However, temperature has a significant effect on concrete mixed with sodium sulfate.The effect of sodium sulfate on the early hydration rate at different temperatures was studied by conducting a time and hydration thermal analysis.The effects of sodium sulfate on the mechanical properties of concrete at different temperatures were studied through compressive strength experiments.Impermeability at different temperatures was studied by testing resistance to chloride ion penetration and resistance to water penetration.The effect of resistance to sulfate attack was also experimentally.The hydration products were analyzed by electron microscopy (SEM) and energy dispersive spectroscopy (EDS).The experimental results showed that at low temperature, sodium sulfate can accelerate the early hydration reaction rate, and the effect becomes weaker with increasing temperature.At low temperature, the addition of sodium sulfate can effectively improve the degree of hydration, and enhance the permeability resistance and ion erosion resistance of the matrix.