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

点击翻译按钮获取中文摘要

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.