Fundamental Study on Freeze-Thaw Resistance of Early-Age Concrete and Its Evaluation Methods

本研究的主要发现如下：1.混凝土试件在水中经历快速冻融循环后，其动弹性模量在试验过程中也有很大程度的增加，用常规方法不能充分评价混凝土的早期抗冻性.如下定义的修正的相对动态弹性模量（REi）可用于有效地评价混凝土在早期的抗冻融性REi（%）= 100 Emi/Eci其中，Emi：在i次冻融循环后测得的动态弹性模量Eci：动态弹性模量在测量Emi时没有内部缺陷的理想状态下，这可以通过未经历冻融循环的样本的成熟度和动态弹性模量之间良好的双曲线相关性来确定。3.在混凝土融后残余应变超过100 × 10 ~（-1）的区域内，<-6>冻融循环次数与残余应变在对数尺度上呈直线关系。使用线性关系的梯度（a）的值通过以下等式计算的量（A）可以是用于充分评估混凝土的抗冻性的方便指标。A = 10 ^a- 14。混凝土的抗压强度要求在其初始阶段不受冻融作用的内部损伤，一般来说，这取决于其水灰比。

The followings are main findings in this research.1. The freeze-thaw resistance of concrete at early ages can not be adequately evaluated by means of conventional method, because the dynamic modulus of elasticity of concrete specimens increases to a great extent during the test even when they are subjected to rapid freeze-thaw cycles in water.2. The modified relative dynamic modulus of elasticity(REi)defined as below can be utilized for a valid evaluation of freeze-thaw resistance of concrete at early ages.REi(%)= 100 Emi/Eciwhere, Emi : measured dynamic modulus of elasticity after i-cycles of freeze-thawEci : dynamic modulus of elasticity In an Ideal state with no inner defect at the time of measuring Emi, which can be determined from a good hyperbolic correlation between the maturity and dynamic modulus of elasticity of specimens subjecting no freeze-thaw cycles.3. In the region where the residual strain of concrete after thawing exceed 100xlO^<-6>, there exists a straight-line relation between the number of freeze thaw cycles In a normal scale and the residual strain In a logarithmic scale. The quantity(A), which is calculated by the following equation using the value of gradient(a)of the linear relation can be a convenient index for adequately evaluating the freeze-thaw resistance of concrete.A = 10^a - 14. The compressive strength of concrete required to be free from the internal damage by freeze-thaw action at its Initial stages differs greatly, in general, depending on its water-cement ratio.