Influence of elevated temperature on creep and relaxation of early age concrete

For the calculation of the restraint stresses in hardening concrete structures, the viscoelastic behaviour of early age concrete has to be taken into account. In addition, as aniso- thermal conditions usually prevail in the structure, the temperature effect on the viscoelastic behaviour has to be taken into consideration. The study based on tests for creep and relaxation of early age concrete under tension, which is reported in this paper, shows that relatively elevated temperatures before loading reduce the creep and relaxation through accelerated aging. On the other hand, during the application of loading, relatively elevated temperatures increase creep and relaxation similarly as it occurs with hardened concrete. Models for creep and relaxation based on experimental results, which take both temperature effects on viscoelastic behaviour into account, have been developed and are presented in this paper.