1991 Fiscal Year Final Research Report Summary
Fundamental Study on Freeze-Thaw Resistance of Early-Age Concrete and Its Evaluation Methods
| Project/Area Number |
02650331
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
コンクリート工学・土木材料・施工
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| Research Institution | University of Tsukuba |
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Principal Investigator |
YAMAMOTO Yasuhiko University of Tsukuba, Inst. of Eng. Mechanics, Assoc. Prof., 構造工学系, 助教授 (40061220)
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| Project Period (FY) |
1990 – 1991
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| Keywords | Early-age concrete / Freeze-thaw resistance / dynamic modulus of elasticity / Evaluation method / Residual strain / Maturity / Cement hydration / 寒中コンクリ-ト |
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| Research Abstract |
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/Eci
where, Emi : measured dynamic modulus of elasticity after i-cycles of freeze-thaw
Eci : 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 - 1
4. 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.
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