| Sulfate attack is one of the important factors that cause the failure of concrete structure,while dry-wet cycle accelerate the corrosion process of concrete caused by sulfate attack.However,there is no national standard about dry-wet cycles that limits the deep development of sulfate attack.To get the most reasonable dry-wet cycle regime,which apply to accelerate sulfate corrosion,4 types of dry-wet cycle were designed（3d、7d、14d、21d）,the dry and wet ratio is 3/1,the specimens were soaking in 5%Na2SO4 and drying in the air under the condition of dry-wet cycles,the mass、the dynamic elastic modulus and the flexural strength were measured in defined period,and SEM test were carried out at 0d、84d、189d.In this paper,the macroscopic properties of concrete such as surface conditions,the relative weight Km,relative dynamic modulus KE and relative flexural strength Kf varied with sulfate attack ages were studied,the cause of macroscopic properties of concrete were analyzed and the damage evolution laws of concrete caused by sulfate attack were revealed based on SEM.The main conclusions are as follows:（1）The mass increased firstly then decreased with erosion age.The dynamic elastic modulus and the flexural strength have the same tendency?decreased firstly then increased,oscillation changes then declined quickly with corrosion ages.（2）In the same dry-wet radio,the longer the dry-wet cycle,the more serious the internal corrosion of the concrete,and the faster the macro-mechanical performance declines in the later stage of erosion within certain range.（3）When the dry-wet cycle is 21d,the corrosion rate is fastest,the macro-mechanical performance of DW21 concrete declined constantly,but the macro-mechanical performance of DW21 concrete continue to growth in the 9th dry-wet cycles.（4）The analysis of the microstructure proved that the internal concrete experienced a vicious cycle of“initial imperfection-packing tightly-the crack-further filling-crack expansion”during the period of sulfate attack. |
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