STUDIES ON FROST DAMAGE OF PRECAST CONCRETE USED TO AGRICULTUREL ENGINEERING

1.即使在蒸汽养护的混凝土中，夹带的空气也提供了很大的抵抗冻融破坏的能力。即使在一天两阶段固化和短的预固化时间下成型的样品中也表现出如此高的电阻。混凝土的抗压强度与耐久性之间没有相关性。预制混凝土的耐久性完全取决于混凝土的引气.预制混凝土在反复冻融作用下，表面气泡面积不断扩大。然而，经过通风训练的预制混凝土即使经过300次冻融循环也没有倒塌。相比之下，普通混凝土仅在90次循环后就倒塌了。本试验结果表明，6.5%是预制混凝土在未硬化状态下的引气量极限。即使在未硬化状态下含气量大于4.5%的引气混凝土中，如果含气量小于4.5%，也不一定能获得高的抗冻融性。 ...更多信息 受电视剧的影响。在预制混凝土工厂中实际测量的振动台上振动期间空气含量的大约50%的减少发生在对于具有2.1%空气含量的素混凝土振动1分钟之后，对于具有4.5%空气含量的加气混凝土振动2分钟之后，以及对于具有6%空气含量的加气混凝土振动4分钟之后。在振动幅度较窄的情况下，空气含量的减少率降低到约1/.7。在本实验中测量的硬化混凝土中的夹带空气含量的范围从最小的2.5%到最大的3.8%。测量表明，气泡的平均空气空隙率为220 μ。即使最大空隙率为254 μ的样品也表现出足够的抗冻性。气泡的粒度聚集以100- 200 μ m以下的气泡为主。这可能表明这些微气泡具有防止混凝土由于冻害而劣化的效果。少

1. Enen in steamecured concrete, the entrained air provides a large resistance against deteriortion by freezing and thawing. Such a high resistance was also demonstrated even in the sample molded with 2-stage curing a day and a short pre-curing time.2. No conrelation was noted between the compressive strength and durability of concrete. The durability of precast concrete depends completely on the entrained air.3. The bubble area on the surface of precast concrete expands by repetition of freezing and thawing. However, airentrained precast concrete did not collapse even after 300 cycles of freezing and thawing. In contrast, plain concrete collapsed after only 90 cycles.4. The present experiment results indicate that 6.5% is the limit of the entrained air content in an unhardened state of precast concrete.5. A high resistance to freezing and thawing may not always be obtained even in air-entrained concrete that had the air content ot 4.5% in the unhardened state, if the air content was r … More educed by vidration.6. An approximately 50% decrease in the air content during vibration on the vibration table as actually measured in a precast concrete plant occurred after 1 minute of vibration for plain concrete with 2.1% air content, after 2 minutes of vibration for air-entrained concrete with 4.5% air content and after 4 minutes of vibration for air-entrained concrete with 6% air content. With an narrower amplitude of vibration, the rate of the decrease in the air content was reduced to approximately 1/.7. The entrained air content in hardened concrete measured in this experiment ranged from the minimum of 2.5% and maximum of 3.8%.8. The measurement revealed that the mean air void fraction of bubbles was 220mu. Even the sample having the maximum air void fraction of 254mu demonstrated an adequate freezi-resistance.9. The grain size accumulation of bubbles was predominated by air bubbles of the size below 100-200mu. This may suggest that these micro-bubbles have an effect of preventing deterioration of concrete due to frost damage. Less