Residual bond strength between steel bars and concrete after elevated temperatures

The effects of elevated temperatures and cooling regimes on the residual (after cooling) bond strength between concrete and steel bars are investigated. For this study, ribbed steel bars of 8 mm diameter are embedded in to C20 and C35 concrete blocks with embedment lengths of 6, 10 and 12 cm. Unsealed specimens are heated to 12 different temperatures ranging between 50 and 700 degrees C and then cooled in water or in air. Pull-out tests are carried out on the specimens, and the effects of elevated temperatures on the residual bond strength are investigated by comparing the results against unheated specimens. Increases in bond strength are observed for temperatures up to 150 degrees C; however, there is decrease for all other temperatures. The effect of the cooling regime is less pronounced for the concrete-bar bond strength. Moreover, it is concluded that concrete-bar bond strength increases with the increase in compressive strength of concrete and embedment length of the bar. (C) 2009 Elsevier Ltd. All rights reserved.