Study on Corrosion Mechanism of Different Concentrations of Na(2)SO(4) Solution on Early-Age Cast-In-Situ Concrete

The deterioration of early-age concrete performance caused by SO(4)(2−) internal diffusion in concrete is a critical factor of concrete durability. In this study, the mechanical properties, heat of hydration, and pore structure of early-age cast-in-situ concrete with different sodium sulfate (Na(2)SO(4)) concentrations were studied. The mechanism of SO(4)(2−) internal corrosion was evaluated by measuring the dynamic elastic modulus, compressive strength, and heat of hydration rate. Scanning electron microscopy, energy dispersive spectroscopy, X-ray computed tomography, X-ray diffraction, thermogravimetry-derivative thermogravimetry, and differential scanning calorimetry were applied to analyze microstructural variations and complex mineral assemblages of concrete samples. The results indicated that during the hardening process of cast-in-situ concrete, Na(2)SO(4) first promoted and then hindered the hydration rate of cement, and also hindered the early strength development of the cement. As the concentration of Na(2)SO(4) solution increases, the corrosion products of ettringite (AFt) and gypsum (Gyp) gradually increase, causing cross cracks in the concrete. The proportion of small and medium pores first increases and then decreases, and the large pores first decrease and then increase. The mechanical properties of concrete gradually decrease and diminish the mechanical properties of the concrete (thereby accelerating the damage to the concrete).