Role of coarse aggregate sizes in evaluating the bond-slip mechanism of reinforced concrete

The bond between steel reinforcement and concrete is vital for the stability and longevity of reinforced concrete structures, especially at beam-column joints. While researchers have explored various factors that affect bond strength, one area that hasn't received much attention is the size of the coarse aggregate. This study focuses on how the size of coarse aggregates influences bond strength, using pullout tests with deformed bars. The team tested aggregate sizes ranging from 9.5 mm to 37.5 mm, comparing these to pure mortar specimens. The results showed a clear trend: bond strength also dropped as the coarse aggregate size decreased. Pure mortar only had 38.65 % of the bond strength of concrete with a 25 mm aggregate. Bond strength prediction models, like the CEBFIP model, also work well for larger aggregates (like 25 mm) but aren't as accurate for smaller ones. These findings highlight the importance of considering aggregate size when designing reinforced concrete, especially in crowded beam-column joints. Future research could dive into other factors, such as aggregate shape and moisture content, to create more accurate models for predicting bond strength in real-world conditions.