| Along with the importance attached to road infrastructure, construction of Grade highways (especially speedway) have being renewed day by day. But early destroy of roads are serious in using years. A phenomenon what base cracked induce surface cracking (also known as reflective crack), as the dominant factor, has been widely concerned. The results show that proper additives can effectively improve the crack condition by maintaining the original gradation level of materials. Taking the actual circumstance of road construction in Inner Mongolia, and the related experience from home and abroad into account, and on the basis of analyzing mechanism of crack formed of semi-rigid base, a performance study for preventing crack is processed by lime stabilized gravel mixed with polypropylene and polyester fibers.That the main achieved work includes:1. With self-made test model, the contrasted experiment adopts two evaluation methods to test the cracking morphology about mixture of lime-fly ash stabilized gravel that has intended gradation. One method is calculating total length of crack by width-right value, and the other is calculating surplus sand quality by pouring 0.075mm sand into the crack. The experiment verified that the polypropylene filament fiber in length 19mm'capacity to resist plastic shrinkage is best and applied to following.2. The paper indicates influence rules of quality proportion of lime-fly ash and of quality of fiber and different curing period by contrasted analysis of basic mechanical properties of primary mixed material and the material of lime-fly ash mixed fiber. Test results show that a small amount of polypropylene fibers in mixture can hardly enhance the compressive strength of lime-fly ash stabilized gravel and maintain the cleavage strength to have no significant fluctuation. But they have important effect for reducing resilient modulus. In addition, the test results reflected that the fiber exist the best mixed rate range.3. Arranging experiment by orthogonal table, and Using dial gauge for dry shrinkage test of lime-fly ash stabilized gravel, the best combination of initial conditions up to the goal of experiment is as following: the quality blended ratio of lime and fly ash is 1:2, the volume ratio of fiber is 2‰, the testing time is closer the molding time of sample and the result is closer the expected data of shrinkage character. The test indicates that the testing time is the most prominent factor of ingredients that work on the water loss rate. 4. According to theory of fracture mechanics, the cracking mechanism of polypropylene fiber acting on lime-fly ash stabilized gravel is discussed by K superposition method. The measure can explain well for function which a series of filament prevent the crack extending.5. The paper establishes structure model of semi-rigid base. By changing the structural parameters of material, the control of ordinary lime-fly ash stabilized gravel's bottom principle charts is compared with the lime-fly ash stabilized gravel mixed polypropylene fiber. The results indicate that: the mixture mixed polypropylene fiber can reduce the principle stress value of bottom of lime-fly ash stabilized gravel. In addition, the software is still used for static simulation of crack tip. Analysis indicates that the region of crack tip has stress concentration, and indicates that fiber can reduce the stress and strain field intensity of the crack tip of mixture mixed with fiber.
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