gtm-use-in-China - USE OF GTM MIX AT SHITAI FREEWAY TO...

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USE OF GTM MIX AT SHITAI FREEWAY TO SOLVE RUTTING PROBLEM AND COMPARISON OF GTM MIX AND MARSHALL MIX BY HEBEI DOT RESEARCH INSTITUTE Ms. Liu Gui Jun, Mr. Wang Qing Kai, Mr. Wang Lian Fang March 2000 Shitai freeway is a major road in a mountain region of Hebei Province. It is a major road for transporting coal out of Shanxi province. Because of steeper grade, high percentage of over-loaded trucks, slow traffic speed, channelized traffic, and higher temperature during summer time, rutting and bleeding were the major problems for Shitai freeway since it was opened to the public in 1995. Pavement repairs began almost right after it was opened to traffic. However, the repaired pavement could only last for a year, and then repair works would have to be done again at the same spot in the following year. Sometimes the repaired pavement lasted only for couple months. All of these repairs caused strenuous problems for the highway authorities and their maintenance crews. Every new idea, method, materials and techniques have been tried. However, the problems were still reoccurring until the adoption of GTM (U.S. Army Corp of Engineers Gyratory Testing Machine) method in 1998. It was the first time that a GTM mix was used in China. Hebei DOT Research Institute purchased GTM in early 1998 and immediately used it for mix design for Shitai freeway pavement replacement project. The GTM method is not like other conventional, empirical methods. The GTM method is a rational method. The GTM can closely model the performance of flexible pavement under traffic load. That enables us to perform pavement stress analysis and design. The actual maximum contact pressure between tire and pavement is used for mix designs to obtain optimum bituminous content, shear strength, shear strain, and density of the mix. The shear strength will then be compared to induced shear stress of the traffic load to make sure that the shear strength to induce shear stress ratio to be greater than 1.0. The shear strain also needs to be controlled to make sure that the ratio of shear strain at termination to intermediate shear strain is less than or equal to 1.0, which is to make sure that the plasticity will not occur. Otherwise, the amount of bitumen needs to be reduced. The density of mix obtained from the GTM represents the ultimate density under traffic load.
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There are two reasons for pavement rutting and bleeding. One is due to continued densification of pavement under traffic loads. The other one is due to the lack of shear strength of the pavement structure elements, especially during summer time. All of these factors have been taken into consideration in the GTM method. Maximum contact pressure is used as a vertical pressure when performing mix design with GTM, and the mix is prestressed to the equilibrium condition (ultimate density under traffic load). The shear strength of the mix is greater than induced shear stress by the traffic load, and the ratio
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This note was uploaded on 05/26/2011 for the course CGN 6505 taught by Professor Mang during the Spring '11 term at University of Florida.

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gtm-use-in-China - USE OF GTM MIX AT SHITAI FREEWAY TO...

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