2007 Fiscal Year Final Research Report Summary
Fracture of the reinforcing bars and deterioration mechanism due to Alkali Silica Reaction
| Project/Area Number |
17360216
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Structural engineering/Earthquake engineering/Maintenance management engineering
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| Research Institution | Kyushu Institute of Technology |
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Principal Investigator |
KOSA Kenji Kyushu Institute of Technology, Faculty of Engineering, Professor (00315160)
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| Co-Investigator(Kenkyū-buntansha) |
INOUE Susumu Osaka Institute of Technology, Faculty of Engineering, Professor (30168447)
UJI Kimitaka Tokyo Metropolitan University, Faculty of Urban Environmental Sciences, Professor (70326015)
HARADA Tetsuo Nagasaki University, Faculty of Engineering, Professor (50136636)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Concrete / Durability / Alkali aggregate reaction / Reinforcing bar / Fracture of reinforcing bar / Load-carrying capacity |
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| Research Abstract |
The following conclusions were drawn from the experiment and analysis focusing on the alkali aggregate reaction :
(1) Research on the expansion characteristics of cores sampled from alkali silica reaction (ASR)-affected structures
Analysis was conducted on 21ASR-affected piers having seriously-deteriorated appearances. Of the 21 piers, six had a core expansion of over 1000×10^6. They showed serious damage exceeding a cumulative crack density of 1m/m^2 or more. Therefore, the core expansion of 1000×10^6 can be used as the reference value for the management and evaluation of deterioration of ASR-affected structures.
(2) Quantitative evaluation of ASR damage to actual structures
The relationship between cracking behavior and compressive strength of cores was obtained from ASR-affected actual structures. It was found that the crack density increased up to 8.0 m/m2, but about 80% of the design compressive strength was retained.
(3) Experiment simulating fracture of reinforcing bars due to alkali aggregate reactions
An experiment simulating ASR expansion was conducted using 1/8 scale specimens modeling actual structures and containing expansion concrete within the specimens. Fracturing of reinforcing bars was well reproduced and the fractured planes showed brittle fracturing similar to that observed in the fractured planes of actual structures. It was also found that the rib shape of reinforcing bars has a significant effect on the crack propagation of those bars. According to the comparison of present bars (8φ) and the former bars (2φ) having different rib shape, cracks caused by concrete expansion propagated for less than 5.0% of the bar diameter in the case of present-reinforcing bars, but that of former reinforcing bars was as large as 80%.
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