عنوان مقاله [English]
In the repair and strengthening operation of hydraulic structures used in various water projects, a common method is to add new concrete to the old concrete. In new conditions, the surface of the new and old concrete must be able to withstand the stresses. In this research, in order to evaluate the tenson strength at the junction of old and new concrete under successive cycles of freezing and thawing, for new concrete from three water-to-cement ratios of 0.4, 0.45 and 0.5 and bubble-making materials with values of 0, 0.1, 0.2, 0.3 and 0.4 percent by weight of cement used, as well as three grades of cement 300, 350 and 400 kg/m3 have been used and 300 consecutive cycles of thawing and freezing were applied after 3, 7 and 28 days of processing. The results of this research show that for the condition with and without the thawing and freezing cycle, the tenson stress increases and decreases with the increase in the weight percentage of the bubble-making material, and in the concrete sample with a processing period of 28 days, the ratio of water to cement is 0.4. , 0.45 and 0.5 and zero consumption bubble, the average tension strength decreases by 69%, 66% and 72%, respectively, and for concrete with 0.4 consumption bubble, it decreases by 14%, 11% and 16%, respectively. Also, after applying the freezing and thawing cycle, the highest and lowest reduction in tension strength occurs in the water-cement ratio of 0.5 and 0.45, respectively.