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.

Porous basalt aggregate is commonly used in roadbed engineering, but its application in concrete has rarely been studied. This paper studies the application of porous basalt in concrete. Porous basalt aggregate is assessed for its effects on mechanical strength and durability of prepared C50 concrete; because it has a hole structure, porous basalt aggregate is known for its porosity, and porous basalt aggregates can be made full of water through changing the content of saturated basalt; after full-water condition is achieved in porous basalt aggregate mixture of C50 concrete, we discuss its mechanical properties and durability. The effects of C50 concrete prepared with basalt aggregate on the compressive strength, water absorption, and electric flux of concrete specimens of different ages were studied through experiments, and the effects of different replacement rates of saturated porous basalt aggregate on the properties of concrete were also studied. The results show that porous basalt aggregate can be prepared as C50 concrete. For early saturated porous basalt aggregate concrete, its compressive strength decreases with the increase of the replacement rate of saturated aggregate; this occurs up to concrete curing at 28 d, when the replacement rate of saturated basalt aggregate is greater than or equal to 40 %. The compressive strength of concrete increases with the increase of the replacement rate of saturated aggregate. The 28 d electric flux decreases with the increase of the replacement rate of saturated aggregate, indicating that saturated porous basalt aggregate can improve the chloride ion permeability resistance of concrete in later stages.