Grant-in-Aid for Scientific Research (A)
|Allocation Type||Single-year Grants|
|Research Institution||Kitami Institute of Technology|
AYUTA Koichi Faculty of Engineering, Professor, 工学部, 教授 (90003186)
SAKAI Koji Hokkaido Development Bureau, Civil Engineering Research Institute, 開発土木研究所, 部長
SAKURAI Hiroshi Faculty of Engineering, Associate Professor, 工学部, 助教授 (80187088)
|Project Period (FY)
1996 – 1998
Completed(Fiscal Year 1998)
|Budget Amount *help
¥8,900,000 (Direct Cost : ¥8,900,000)
Fiscal Year 1998 : ¥1,100,000 (Direct Cost : ¥1,100,000)
Fiscal Year 1997 : ¥1,800,000 (Direct Cost : ¥1,800,000)
Fiscal Year 1996 : ¥6,000,000 (Direct Cost : ¥6,000,000)
|Keywords||Concrete / Frost Resistance / Ice Sea Region / Evaluation of Durability / Mechanism of Frost Damage / Exposure Test / Antiwashout Underwater Concrete / Plastic Micro-spheres / 促進試験 / 劣化予測 / 信頼性モデル / 凍結機構|
1. Mechanism of Frost Damage of Concrete Effected by Seawater
According to differential scanning calorimetry, the endothermic curve of specimens immersed in seawater is broader than that of specimens in fresh water. The thaw temperature distribution of specimens in seawater widens with time.
A specimen immersed in sea water has greater number of pores of size several ten to thousand nm as aging proceeds. The total pore volume is also much higher, so the amount of frozen water increases in the case of sea water.
These indicates that concrete immersed in seawater is easily subject to frost damage.
2. Deterioration Prediction of Concrete by Reliability Theory
To examine deterioration prediction of concrete structure by reliability theory, we analyze the data of concrete specimens during rapid freeze-thaw tests and exposure tests, and mortar specimens during tensile strength tests.
From these examinations, we conclude that when the water cement ratio is low, the reliability is high. The service
life and repair plan of concrete structures can be estimated as time on index of reliability 75%, 95%, etc.
3. Frost Resistance of Antiwashout Underwater Concrete
It is difficult to form a suitable air-void system in concrete in which air-entraining agents and sonic special admixture, such as antiwashout admixtures containing cellulose, are used together.
We have introduced plastic micro-spheres (EPM) instead of air-entraining agents to improve the frost resistance of antiwashout underwater concrete with cellulose ether as an antiwashout admixture. As a result, frost resistance of concrete is improved with the addition of 1.0% EPM and 60% blast-furnace slag with fineness of 8000 g/cmTAU12@E1
4. Deterioration of Large Concrete Specimens Exposed to Seawater in Cold Climate
About fifty large specimens, each have about two or three tf in weight, have been exposed at the seashore in Hokkaido Island, Japan for ten years to clarify the effect of materials, mix proportions and others on the frost damage.
The degree of the scaling is different by the parts or the mix proportions of specimens. The scaling occurred severely at the position of the specimens which were exposed to more freezing and thawing cycles or were at high degree of saturation. Less