Creep Model of Concrete at Early Ages

混凝土的徐变行为已被许多研究者所研究，但几乎所有的研究都与成熟混凝土有关。为防止大体积混凝土中水泥水化热引起的裂缝，进行了这项研究。对早龄期混凝土进行了1d~5d的抗压徐变和抗拉徐变试验。重点研究了加载年龄、加载时间、应力水平等因素对加载效果的影响。压缩蠕变试验表明，当应力水平低于抗压强度的50%时，比蠕变不受影响，而当应力水平超过50%时，比蠕变显著增加。应力水平和比蠕变的影响随加载龄期的增加而减小。另一方面，从拉伸蠕变实验中发现，当应力水平超过抗拉强度的20%时，比蠕变不是恒定的，并根据实验结果研究了应力变化的建模方法，并对超位移法对该应力变化的适用性进行了评估。指出对Voigt模型进行修正后提出的徐变模型适用于早龄期混凝土，而超位移法同样适用于压应力水平低于强度50%的温度应力等变化应力。

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, term of loading, and stress level so on. 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. On the other hand, it was noted from tensile creep experiments that specific creep was not constant with influence by stress level over 20% of tensile strength.Furthermore, 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 which compressive stress level was below 50% of strength.