The effects of material properties on bond strength between reinforcing bar and concrete exposed to high temperature

The effects of material properties on bond strength between reinforcing bar and concrete exposed to high temperatures are investigated extensively using modified pullout tests. The specimen parameters include various bar diameters, rebar grades and concrete strengths. Three different concrete cubes with compressive strengths of 20, 34 and 44 MPa, 12, 16 and 20 mm rebar diameters and S220a, S420a and S500a rebar grades were utilized for the tests. In the experimental study, the tests were conducted on 150/300 cylinder specimens in which rebars are embedded vertically exposed to high temperatures (100, 200, 400, 600 and 800 °C) and cooled down. Furthermore, 150 mm cube and 100/100/300 mm prism specimens were used to determine compressive and flexural strength of concrete. Bond strengths of these specimens were compared with each other and then with unheated specimens at 20 °C. Experimental results indicated that residual bond strength between reinforcing bar and concrete decreases with increasing temperature. The first severe bond strength loss was observed for grade S220a at the range of 200-400 °C and for grade S420a and S500a at the range of 400-600 °C. The residual compressive strength is in tendency with the residual bond strength of S420a and S500a whereas the residual flexural strength corresponds agrees with the residual bond strength of S220a.