Performance degradation and microscopic structure of rubber/concrete after salt freeze-thaw cycles

The normal concrete (NC) and rubber/NC were prepared. The performance degradation process of concrete specimens within 60 salt freeze-thaw cycles was studied, which includes changes of apparent phenomenon, flaking amount and compressive strength loss. The adaptation of ultrasonic test in evaluating the performance of concrete after salt freeze-thaw cycles was investigated. The relationships between relative velocity, damage degree and compressive strength were comparative analyzed. The micro-structure changes of concrete specimens after salt freeze-thaw cycles were observed by SEM. The results show that the surface erosion of concrete becomes more obvious, the flaking amount, internal damage and strength loss gradually increase, with the increasing number of salt freeze-thaw cycles. It has good correlation between the ultrasonic parameters and compressive strength. After the concrete undergoing salt freeze-thaw damage, the internal structure becomes loose and flocculent, increasing pores and cracks appear, and the density decreases, which results in deterioration of macro-mechanical properties. However, the deterioration degree of rubber/concrete is better than that of normal concrete at all cycle stages, because the elastic rubber fine aggregate can effectively alleviate internal cracking and pore expansion caused by icing pressure. The rubber/concrete with 10% rubber content (mass ratio to cementitious material) (10%Rubber/NC) has the best performance indicators. After 60 salt freeze-thaw cycles, the compressive strength loss rates of normal concrete and 10%Rubber/NC are 58.5% and 48.0%, respectively.