| Research Abstract |
Ultra-Thin White-topping was originally developed in Northern Europe and America to rehabilitate severely rutted asphalt pavement Since then this method has been spread around the world. In Japan, this method has been tried in several sites as a trial and performance data have been collected. The performance data revealed that the white-topping structures is able to withstand at least medium traffic conditions for more than 5 years. On the other hand, Ultra High Strength Fiber Reinforced (UFC) has been developed and applied on several actual structures. Because-UFC has a very dense matrix and contains short fibers, it has excellent mechanical properties and durability compared with conventional concrete. Combining these two technologies, Ultra-thin white-topping structure with high strength concrete (HSCWT) was developed. In this method, 1.0m by 1.7m panels with a thickness of 30mm, which are prefabricated in a factory under very good curing conditions, are placed over an existing asph
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alt pavement The flexural strength of the HSC panels is more than 40MPa, which is much higher than normal concrete slabs. The panels are bonded with the asphalt layer by grouting the gap between them. For rational structural design of the HSCWT, mechanical behavior of the structure should be thoroughly understood. Although the HSC panels have very high flexural strength, the stresses in the panels due to traffic loads are expected to be very high and strongly depending upon the stiffness and thickness of the underlying asphalt layer. Furthermore, since the asphalt layer is much thicker than the panels, the visco-elastic nature of asphalt layer could not be ignored.
In this study, in order to establish the structural design method for HSCWT, accelerated loading tests were conducted on full scale test pavement of HSCWT and long-term performance was investigated. 3DFEM analysis was performed to simulate the tests and address the structural features of HSCWT. Based on the analysis of loading tests and FEM calculations, a structural design procedure was discussed. The results of this study are summarized in the following.
(1) Accelerated loading tests.
Test pavements of HSC-WT were constructed on an accelerated loading facility and were subjected to moving axle loads about 150, 000 to 200, 000 times. From the test results, following remarks can be made :
● Unbonded area developed from joint between panels, which might cause weak support for the panels and promote very fine surface cracking.
● Stone and coin texture types on the bottom face of the panel effectively enhanced the bonding, while hole type of texture formed air void at the interface and weakened the bonding.
● No serious problems under traffic loads raised on long term performance of HSCWT, as long as a sound bonding was ensured at the interface between the panels and the asphalt layer.
● Joint reinforcement with underlying panels was not good measure.
(2) FEM analysis
Based on analysis of the loading tests with dynamic 3DFEM and comparison of the computer results with the measured data, visco-elastic parameters of the asphalt layer were identified. Mechanism behavior of HSCWT was investigated based on dynamic analysis of the loading tests with 3DEFM. Following remarks can be made :
●For the summer loading test, low viscosity in the asphalt layer was identified, while for winter loading test, relatively high viscosity was identified.
●Stresses in HSC panel was affected very little by visco-elastic parameters and loading rate. The most significant effect was the interface condition between the panel and grout.
●Stresses in the panel much less than the strength of HSC panel if good bonding at the interface was ensured. Therefore the fatigue of the panel would not be an issue in the structural design of HSC-WT.
(3) Structural design method
Based on the results of the accelerated loading tests and FEM analysis, a mechanical design procedure for HSCWT was developed. In the procedure, tensile strains in the underlying asphalt layer are calculated with 3DFEM and fatigue damage of the asphalt layer is estimated from the tensile strains using fatigue curve of asphalt mixture. It was found that not only viscosity of asphalt layer but also vehicle speed significantly affects fatigue life of asphalt layer. Less
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