Structural behaviour of reinforced concrete beams with different types of joint configurations linked by old to new epoxy treatment

Abstract

This study experimentally investigates the structural behavior of reinforced concrete (RC) beams with different construction-joint configurations treated using an Old-New epoxy bonding agent. Eleven simply supported RC beams with dimensions of 250× 300 × 1850 mm and a concrete grade of 35 MPa were cast and tested under two-point loading. The experimental program included one monolithic reference beam and ten jointed beams cast in two stages with a 24-hour interval. The investigated joint configurations were a 45° inclined joint, a 90° vertical joint, a horizontal joint, and a key joint located in the flexural zone, in addition to a 90° vertical joint located in the shear zone. For each joint configuration, one specimen was left untreated, while the corresponding specimen was treated with Old-New epoxy before the second concrete pour. The beams were evaluated in terms of ultimate load, first visible cracking load, load–deflection response, stiffness, ductility, toughness, strain behavior, and crack pattern. The results showed that construction joints reduced the ultimate load compared with the monolithic reference beam, with untreated specimens showing reductions between 8.3% and 13.1%. The epoxy treatment improved the ultimate load of most flexural-zone joints, especially the 90° vertical flexural joint, which achieved a 7.16% increase compared with its untreated counterpart, although it remained 4.5% below the reference beam. The treatment also enhanced cracking resistance, increasing the first visible cracking load by 68.1% for the 90° flexural joint and 88.4% for the 90° shear-zone joint. However, the shear-zone joint showed a 7.01% reduction in ultimate load after treatment, indicating that epoxy alone was less effective under shear-dominated interface conditions. Overall, the Old-New epoxy treatment was more beneficial for flexural-zone joints than shear-zone joints.