experimental study of bond strength between fresh and old concrete

todays applying concrete structures is more usual than other structures which are used in buildings as in most of the world’s countries the application ratio of concrete to steel has increased from 10 to 1. sometimes these structures require strengthening vulnerable members because of deficiency in their loading system in usual and critical conditions. there are different methods for strengthening these members. one of them is developing dimension of section by fresh concrete. in this method, the cohesion extent of fresh concrete to hardened concrete has significant role in force transfer.in this experimental project, the bond stress created between hardened concrete (core) and fresh concrete (screen) in core samples was measured and the effect of changing three factors was investigated that they are the length of sample, screen thickness, and 28 days compressive strength of screen concrete on bond stress. the push-out method was applied in this experiment for cracking the samples.