Case Studies in Construction Materials 17 (2022) e01565 Available online 13 October 2022 2214-5095/© 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Residual bond strength in reinforced concrete cracked by expansion agent flled pipe simulating rebar corrosion Amadou Sakhir Syll a, * , Toshiyuki Kanakubo b a Graduate School of Systems and Information Engineering, University of Tsukuba, Japan b Division of Engineering Mechanics and Energy, University of Tsukuba, Japan A R T I C L E INFO Keywords: Bond strength Concrete cracking Rebar corrosion Expansion agent Induced crack width Residual bond Stirrup-confnement ABSTRACT In corroded reinforced concrete, the volume of steel increases due to expansive corrosion prod- ucts, leading to cracking of concrete. As a result, the bond capacity between concrete and rebar gradually decreases. Previously, the author explored bond deterioration owing to corrosion- related cracking using a novel crack simulation approach. To simulate the volumetric expan- sion of the rebar due to corrosion, an aluminum pipe is inserted into the concrete and flled with an expansion agent. However, the previous study did not consider the important effect of stirrups that provide confnement and improve bond strength. To address this limitation, pull-out tests were performed on 48 cracked specimens to investigate bond deterioration considering the in- fuence of crack width and stirrup. It is concluded that the induced cracks without corrosion products can measure the exclusive result of corrosion of the rebar itself. After cover cracking, stirrups become the primary confnement source and can help reduce bond deterioration. Finally, an empirical formula was proposed to evaluate the bond strength degradation with induced crack width and stirrups being the main parameters. Comparisons with various experimental results of corroded specimens confrm that the proposed formula can give satisfactory predictions. 1. Introduction The bond between concrete and steel reinforcement bar (rebar) is an essential property of reinforced concrete (RC). It enables the transfer of force from the rebar to concrete and ensures the composite action of the RC members [1]. The confnement conditions for rebars strongly infuence the bond performance of rebars in concrete. The confnement is generally brought by the surrounding concrete, stirrups, and hoops, acting as transverse pressure. Corrosion of rebar is the most severe degradation process that can damage RC members. Researchers [2,3] have established that the bond is more vulnerable to corrosion. According to Auyeung et al. [2], the bond strength deterioration of corroded RC steel specimens is signifcantly more critical than the cross-section loss. They discovered that a diameter reduction of 2% may cause a bond loss of 80%. In addition, the research by Li and Zheng [3]shows that the bond deterioration varies more than the loss in stiffness and strength. Corrosion leads to an expansion of steel volume, creating internal hoop stress in concrete. A small corrosion level can boost the bond strength. However, higher corrosion levels lead to concrete cracking, causing bond degradation due to the signifcant deterioration of the confnement [4–6]. Conventionally, researchers conduct a pull-out or beam test on artifcially corroded specimens to investigate the bond degradation * Corresponding author. E-mail address: s2030203@s.tsukuba.ac.jp (A.S. Syll). Contents lists available at ScienceDirect Case Studies in Construction Materials journal homepage: www.elsevier.com/locate/cscm https://doi.org/10.1016/j.cscm.2022.e01565 Received 26 August 2022; Received in revised form 7 October 2022; Accepted 11 October 2022