Abstract：Cement material is studied in sulfate-dry-wet cycle-freeze-thaw cycle-load under the action of the four factors of degradation process,and using scanning electron microscope(SEM) to observe the microstructure evolution of concrete.The results show that compared with single sulfate erosion,other factors have speeded up the concrete damage.The higher the strength of concrete show a good erosion resistance,sulfate concentration is higher,the faster the degradation of concrete,compared with the physical and chemical erosion,freeze-thaw occupied the main erosion factors.Through SEM observation,it is found under dry-wet cycle-sulfate environment,sodium sulfate crystals generated inside the concrete filling pore,when the crystal pressure reaches tensile strength of concrete,concrete cracks and damages.

Keyword：sulfate environment;scanning electron microscope(SEM);dry-wet cycle;freeze-thaw cycle;fields coupling;microstructure;