Tensile Creep of Concrete at Early Ages

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Creep behavior of concrete has been studied by many researchers, but almost all of them are concerned with matured concrete. This study has been conducted for prevention of cracking due to heat of hydration of cement in massive concrete. Compressive and tensile creep experiments have been carried out for early aged concrete such as from 1 day to 5 days. This study was focused on the influence of age of loading, stress-strength ratio, term of loading and temperature in curing and loading. The following results are obtained.(1) It was noted from compressive creep experiments that specific creep was constant with no influence by stress level below 50% of compressive strength, however, that specific creep significantly increased at over the value. And the influence of stress level and specific creep decreased corresponding to age of loading.(2) From tensile creep experiments it was cleared that the effect of the stress-strength ratio was significant and its relationship with creep strain could be described by an exponential equation. The age of loading influenced only the results of loading at 1 day, but little effect was observed in other age of loading. Aithouth the effect of curing temperature and term of loading could be assessed by equivalent periods of hydration, temperature effect during loading was much significant.(3) The method of modeling for change of stress has been investigated based on experimental results and applicability of super-positioning method for such stress has been assessed. It could be pointed out that a presented creep model which was modified Voigt model is applicable for early aged concrete and super- positioning method also could be applied for changing stress such as thermal stress.