2021 Fiscal Year Annual Research Report
RC構造物の補強に用いるPCM-コンクリート界面の革新的接着工法
| Project/Area Number |
20J20854
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| Research Institution | Hokkaido University |
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Principal Investigator |
Mizan Mahmudul Hasan 北海道大学, 大学院工学院, 特別研究員(DC1)
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| Project Period (FY) |
2020-04-24 – 2023-03-31
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| Keywords | Polymer cement mortar / overlaying method / premature debonding / interfacial strength / silica fume |
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| Outline of Annual Research Achievements |
The aim of the intended study is enhancing the interfacial bonding performance between substrate concrete and PCM to prevent the premature debonding failure and increase load-carrying capacity. Till now, lot of microscopic, material and member level tests were conducted to evaluate the influence of silica fume on concrete-PCM interface. Lower Ca/Si ratio observed through SEM-EDS, a decrease in Ca(OH)2 content observed qualitatively through XRD analysis and quantitatively through TG-DTA at the modified 5% silica PCM-concrete interface compared to normal PCM-concrete interface confirm the extend of bond formation between silica compound and free Ca(OH)2 contributing to the improvement of the interfacial performance. Several tests conducted at material level under tensile and shear stress condition considering experimental parameter such as surface roughness of concrete, compressive strength of concrete, moistness of the concrete interface, early ages behaviour and environmental condition (freeze-thaw cycle, elevated temperature and moisture content) confirmed higher interfacial strength and fracture energy, lower pure interface fracture mode in modified 5% silica PCM cases compared to normal PCM cases. At member level, PCM strengthened RC beams with silica fume showed higher initial slope and stiffness, higher yielding, debonding and ultimate load and flexural or crack along tensile bar instead of pure interface crack. In conclusion, the data accumulated from many experiments confirmed the significant influence of silica fume on concrete-PCM interfacial bond.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The primary focus of this research work was to enhance the concrete-PCM interfacial bond by using silica fume with PCM as a repair material to prevent premature debonding failure which was reported in the technical literature as one of the major failure mode of PCM strengthened RC beams. A large number of experiment considering the influence of different factors that have significant influence on the interfacial bond were performed in microscopic, material and member level. In addition, the bonding durability of concrete-PCM interface with the inclusion of silica fume under environmental conditions (freezing-thawing cycle, elevated temperature and moisture content) were performed as long-term performance of strengthened members is consider more important than short-term bonding strength of newly overlaid PCM layer. The outcome of microscopic and material level experimentation confirmed that the use of silica fume can achieve adequate bond strength with concrete substrate and there is a higher possibility of chemical reaction at the concrete-PCM interface with silica fume addition that can enhance the chemical bonding between the concrete substrate and overlay material. The results of yielding load, ultimate load and failure mode of the strengthen RC beam with/without silica fume confirmed that the inclusion of silica fume has an excellent reinforcing effect on the members. In conclusion, the data accumulated from many experiments showed usefulness to achieve the purpose of this research. Therefore, it can be judged that the research has progressed as expected.
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| Strategy for Future Research Activity |
The experimentation conducted under tensile and shear stress conditions at material level considering many experimental condition (as a priority basis) confirm the positive influence of silica fume with PCM as a repair material to achieve adequate bond strength with concrete substrate. To understand more precisely (quantitatively) the influence of silica fume in forming chemical bonding at the interface to enhance interfacial bond, microstructure analysis is intended to be done using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and thermogravimeter-differential thermal analysis. Bonding test is also intended to perform to develop general interface model in order to use during finite element analysis. In addition, parts of four-point bending tests of strengthened RC beam with and without silica fume as repaired material will be conducted with the aim to use silica fume in practical PCM strengthening technique. Three type of strengthening material: conventional reinforcement, CFRP grid and CFRP strand sheet will be used as a strengthening bar. To reduce end peeling to occur (one of the main failure mode observed in our preliminary test) due to high stress concentration at the end, FRP u-strip will be attached at the end of the overlay. Strain gauges will be attached to the strengthening and the main reinforcement to get strain distribution. Finally for the validation of the experimental beam test result, numerical simulation and analytic analysis will be done to confirm the applicability of this strengthening method.
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