The unexpected temperature drop during the concrete curing process could degrade the concrete properties at early age, and then decrease the bond behaviour between concrete and reinforcing steel bars. To assess the effect of low curing temperature on structural safety, it is significantly important to investigate the bond behaviour of early age concrete under such extreme environmental conditions. In this study, pull-out tests were conducted on the early-age concrete specimens with embedded deformed steel bars at the low curing temperature of 0 °C and the normal temperature of 20 °C. All specimens were subjected to biaxial lateral pressures varying from 0.1 fcu to 0.4 fcu to investigate the effect of simultaneous confining pressure. The results indicated that comparing with the specimens cured at 20 °C, the bond strength for the specimens cured at 0 °C decreased significantly at earlier ages of 3 and 7 days. However, the bond strength increased steadily with the increase of the curing age. Eventually, the concrete specimens at the 28-day age reached the same bond strength for both low and normal curing temperatures. In addition, the average slip displacements corresponding to the bond strengths for the specimens at the low curing temperature was slightly lower than those at the normal curing temperature. Based on the experimental results, an empirical model of bond stress-slip relationship was proposed for the early age concrete at low curing temperatures. Comparing with other existing models, the proposed bond stress-slip relationship agreed well with the experimental results, validating its applicability for the early age concrete at low curing temperatures.
- bond behaviour
- early age concrete
- biaxial lateral pressure
- low curing temperature
- bond stress-slip relationship