Study of 8,000 Cycles Freezing and Thawing Tests in Air by RC Model Specimen using Non-linear Exponential Function Models

The rapid freezing and thawing test specified by ASTM C.666 is carried out in water. However most concrete structures in cold regions are influenced by freezing and thawing in air. The purpose of this study is to evaluate the durability of reinforced concrete under the influence of rapid freezing and thawing in air. The specimens are reinforced concrete models(RC model specimens)of size 10×10×40 cm. The results of rapid freeze-thaw tests in air indicate that concrete specimens with a water-cement ratio of 65％ deteriorate more than specimens with lower water-cement ratios. Further，the durability of concrete with a high water-cement ratio，such as 65％，begins to decrease after 2800 freeze-thaw cycles in air. A nonlinear exponential function model fitted very well to the results of ultrasonic velocity measurements before and after cyclin