Influence of recycled coarse aggregates on the bond behavior of deformed bars in concrete

To investigate the bond behavior of deformed bars in recycled aggregate concrete (RAC), 144 tests were performed. In this paper, the following variables were considered: the aggregate size, four types of recycled coarse aggregate (RCA) replacement ratios, two reinforcing bar directions (vertical and horizontal), and two reinforcing bar locations (75 and 225 mm from the bottom). In addition, the effect of concrete aging on the bond behavior between the bar and the concrete was evaluated. Based on the test results, the RAC-I specimens (with 20 mm of maximum RCA size) had a greater bond strength than the RAC-II specimens (with 25 mm of maximum RCA size) under the same RCA replacement ratio. Thus, the bond strength of RCA is affected by the aggregate size because the shape of the RAC is generally spherical. For both RAC-I and -II specimens, as RCA replacement ratio increased, compressive strength showed a tendency to decrease proportionally. In terms of aging, regardless of the RCA replacement ratio, RAC-I pullout specimens showed similar bond strength under the same age although the compressive strength showed a downward trend with the RCA replacement ratio. In view of the top-bar effect, a significant difference was detected between the top and bottom bars at all ages; this does not confirm the provision of the ACI and CSA codes that require all of the top bars to have more than 300 mm of concrete below them. In particular, the bond stress was not uniformly distributed along the length of the bar in the RAC-II specimens due to settlement of the coarse aggregates.