Abstract
12 pullout tests and 18 push out tests were carried out under different concrete covers and the test results were compared and analyzed. When the ocncrete cover is thin, the specimens split no mater wehther they are under pullout conditions or push out conditions. While when the concrete cover is thick enough, the bars for the push out specimens would be pushed out slowly and the concrete didn't split. Tensile bond strength as well as compressive bond strength of high strength bars increases when the concrete cover becomes larger. In addition, the concrete cover influence much on the tensile bond strength of the bar under a certain limit value range.