| dc.description.abstract | The bond in a reinforcement concrete (RC) structure is represented by the force transfer between the reinforcing bar and the surrounding concrete. All the RC structures are designed to have a perfect bond between the reinforcing bar and the surrounding concrete. However, corrosion of the reinforcing bar in the RC members is one of the main reasons that affect the bond efficiency in RC member. The deterioration of bond in RC element leads to decrease the service life of the RC structure and may result in sudden failure. Most of the previous research focuses on repairing the corroded RC member with FRP wrapping without cleaning the corroded reinforcing bar.
The present research investigated the bond behaviour of cleaned corroded reinforcing bar repaired with partial depth repair concrete, transverse reinforcement or fiber reinforced polymer (FRP) sheets. Thirty-six beam-end specimens and twenty-four lap splice beams were cast and tested under static loading. The beam-end dimensions were 600 mm in length, 500 mm in height and 250 mm in width and reinforced with 20M bar. The test variables considered for the beam-end specimens were: four corrosion levels (5%, 7.5%, 10% and 15% mass loss level) and compared with non-corroded bar. Also, four bonded lengths were studied (200 mm, 250 mm, 300 mm, and 350 mm). Moreover, four partial depth repair concrete were used (commercial prepackaged self-consolidating concrete (SCC1), another different commercial prepackaged self-consolidating concrete (SCC2), self-consolidating concrete that was mixed in place and had similar proportions to the monolithic mixes (SCC3) and normal concrete (NC) mix design was also cast in place and had exactly the same proportions as the monolithic mixes but was used as a partial depth repair). All of the partial depth repair concretes were compared with monolithic beam-end specimen.
The lap splice beams dimensions were 2200 mm in length, 350 mm in height and 250 mm in width and reinforced with two 20M lap spliced bars in the tension zone of the constant moment region with 300 mm splice length. Also, the lap splice beams were reinforced with two 10M continuous bars in the compression zone. The test variables considered for the lap splice beams were: commercial prepackaged self-consolidating concrete extended with 50% of 13 mm coarse aggregate (SCC50) was used as the main partial depth repair. It should be mentioned that SCC50 was the same partial depth repair concrete (SCC2) used for the beam-end specimens. Also, Three lap splice beams repaired with commercial prepackaged self-consolidating concrete without coarse aggregate (SCC0) were also included to study the effect of coarse aggregate on bond behavior. The lap splice beams repaired with partial depth repair concrete were compared with monolithic lap splice beam. Moreover, two types of confinements were considered in the lap splice beams: transverse reinforcement and carbon fiber reinforced polymer (CFRP) sheets. Six lap spliced beams were confined with transverse reinforcement and six were wrapped with CFRP sheets.
This research found that the average bond strength increased as the bar mass loss increased for all bonded lengths. As the bonded length increased, the average bond strength decreased and the corresponding bar slip increased. In the beam-end specimens, the average bond strength of monolithic beam-end specimens was higher than the average bond strength of all types of the partial depth repair regardless the compressive strength of concrete. That was mainly because of internal shear cracks at the interface between the partial depth repair and the substrate concrete. However, since there was not shear at the constant moment region in the lap splice beams, the lap splice beams repaired with partial depth repair concrete with similar properties of monolithic concrete and had higher concrete strength showed higher average bond strength than the monolithic lap splice beams. Although the partial depth repair concrete SCC0 had higher compressive strength than SCC50 and the monolithic concrete; it had the lowest average bond strength. That because the absence of the coarse aggregate in SCC0 led to a decreased splitting strength and reduced fracture energy; and so the average bond strength was decreased. All self-consolidating concrete (SCC) partial depth repairs showed better bonding than the normal concrete (NC) partial depth repair. The bond strength of beams repaired with FRP sheets was higher than that of the beams confined with transverse reinforcement. The transverse reinforcement increased the average bond strength and the corresponding slip by (15% - 29%) and (32% - 62%) compared to the unwrapped beams, respectively. However, the beams confined with FRP sheets showed an increase in the bond strength and the corresponding slip by (34 - 49%) and (56 - 260%) compared to the unconfined beams, respectively.
A multiple linear regression analysis was conducted to predict the effect of mass loss level, bonded length and presence repair concrete on the average bond strength of beam-end specimens. Also, a model was calibrated to predict the average bond strength with increasing the mass loss level of the reinforcing bar of lap splice beams. Moreover, another model was used to allow the design engineers to estimate the bond stress distribution along the spliced reinforcing bars as the splitting crack propagated. | en |
