STUDY ON BOND-SLIP PROPERTIES BETWEEN STEEL BARS AND RECYCLED CONCRETE AFTER FREEZE-THAW CYCLES

Pull out tests of steel bars in recycled concrete after 0, 25, 50, 75 and 100 freeze-thaw cycles are carried out for recycled concrete of 100% recycled coarse aggregate. The influences of freeze-thawing cycle numbers, cover thickness and anchorage length are analyzed. The results show that the bond strength decreases and the slip increases gradually with the increase of the numbers of freeze-thaw cycles; the bond strength is proportional to the increase of relative cover thickness and it is inversely proportional to the anchorage length. However, when the relative cover thickness and the anchorage length increases to a certain value, the bond strength remains almost constant. The bond-slip curve of recycled concrete can be divided into five sections, that is, micro-slip, slip, slip speed-up, inelastic descending and residual stage. Based on the analysis of the experimental data, an empirical formula for characteristic values under different influential factors is proposed, which may provide reference for durability design of structures composed of recycled concrete in freeze-thaw environment.