Mechanism of Reflection Cracks 

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Numerous studies show that the basic mechanisms of Reflection Cracks is tension fatigue, tensile yield to shear yield. Under their joint or individual action leads to reflection cracks. Over time the temperature change and grassroots sizing, so that the surface layer is subjected to tensile force caused by the tension fatigue, cracks and cause cracks extend vertically to the road surface. Extended temperature change rate is the magnitude of the grassroots, the grassroots length of the plate, base material properties and temperature resistance properties of this surface layer fatigue and other factors, such fatigue in the surface layer is thin plate or substrate long road on particularly evident. On the surface, due to the poor thermal properties of asphalt mixture, its upper, middle and lower temperature variation amplitude difference, combined with the cold weather and shrinkage of the surface layer with the grass roots, the combined effects of warping, resulting in large temperature variations generate large surface ultimate tensile strain exceeded the yield strain of the materials used, cracks under tension, which gradually expands downward to form a "on a wide, narrow" crack, called the tensile yield. Since the formation of grass-roots cracking the plate, when the vehicle passes, the vertical displacement of adjacent plates difference between the ends, causing the surface layer in the surface layer shear fatigue lead to cracking, adjacent plates Primary role in interlocking links complete after the destruction, this is why the shear fatigue cracks. Reflective Crack propagation velocity by long semi-rigid base plate, base crack affect the rate, the smaller the plate length and increased fracture rate decreased surface layer yield failure. Asphalt content of asphalt coagulation compound, bitumen grade, aggregate gradation, porosity and thickness of the surface layer of paving are influential tension fatigue life. Pavement Structure under external loads, stress situation is more complex, after the introduction of three-dimensional photoelastic model of experimental research - rigid base cracking under traffic loads, the stability of the state near the stress cracks and fractures, as well as the effect of stress crack absorbing film, It concluded that: the semi-rigid crack, this crack is unstable, crack tip stress stripes very intensive, under partial load action will cure the direction parallel to the crack extended to the road surface. Improve semi-rigid material breaking toughness, can prevent cracks. Low modulus, high stress absorbing film of deformable material, which can effectively prevent reflection crack.

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  Friday, September 16, 2016 at 4:16:22 AM

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