Post-yield bond behaviour of deformed bars in high-strength self-compacting concrete

• A high-strength self-compacting concrete mix (approximately 90 MPa) was developed.
• A comparable conventionally vibrated high-strength concrete mix was also developed.
• Post-yield bond between deformed bars and both concretes was investigated using pullout tests.
• Significant difference was observed between the bond strength of 300 and 500 MPa grade bars in post yield range.
• Reduction of bar diameter in post-yield range was found to be the main culprit for bond discrepancy.

Self-compacting concrete (SCC) has gained substantial attention since its advent for its ability to compact without the need for either internal or external vibration even in areas of highly congested reinforcement such as beam-column joints. During the past two decades, extensive research has been conducted on both the fresh and hardened properties of normal strength SCC; however, only recently has interest in high-strength self-compacting concrete (HSSCC) gained momentum.This study investigates bond properties between reinforcement and HSSCC as well as conventionally vibrated high-strength concrete (CVHSC). Appropriate mix designs for both HSSCC and CVHSC were first developed to achieve comparable concrete compressive strength of about 90 MPa. The effects of bar grade, diameter, bond length, and concrete type were investigated by means of pull-out tests for both concrete types; where, special attention was paid to the post-yield slip behaviour of different steel grades. It was found that the difference in ductility of bars with different grades results in different rate of diameter reduction due to axial tensile stress which consequently affects their bond performance; especially in the post-yield range. Available bond models were applied to the experimental outcomes of this study and modifications and/or new expressions are suggested where possible.