Study On Asphalt Overlay Design Resisting Reflection Cracking

Currently, cement concrete pavement repair and overlay treatment is a difficultand hot issue. In practical engineering, the asphalt surface layer is one of the mosttypically used reinforcement methods. According to current engineering experience,reflection crack is the main and the most destructive crack form in old cementconcrete pavement which has asphalt concrete surface layer. The appearance ofreflection crack will continuously lead water into the road structure from cracks.Thusthe strength and stability of sub-grade is affected, making the road-carrying capacitydecline, which will generate a series of damages.This phenomenon affects thecomfort of driving and increases the maintenance-cost for asphalt overlay. Moreimportantly, under the influence of repeated action of vehicle load and periodicalchange of environment＆temperature, cracks rapidly extend all around, thus greatlyshortening the service life of the overlay. Therefore, it is of great significance to putforward the design method for asphalt overlay to control the crack forms, boththeoretically and practically.The thesis firstly analyzes the formation mechanism and propagation mode ofreflective crack. Then by establishing a three-dimensional finite element model, theinfluence of different parameters onto asphalt overlay stress condition is fullyanalyzed (parameters: asphalt overlay modulus, thickness, atmospheric temperaturechanges etc.) The above analysis provides a theoretical basis for the design methodsfor asphalt overlay to control the reflection cracking. Among which, the decrease intemperature makes the asphalt overlay easy to produce a larger tensile stress, Vehicl eload makes the asphalt overlay easy to produce a larger shear stress.The commonlyused measures for preventing reflection cracks respectively have both advantages anddisadvantages, and these measures have different influence towards the stresscondition of asphalt overlay. In view of this, the thesis puts forward some relevantsuggestions.In order to control the formation and propagation of reflective cracks, the thesisputs forward an asphalt overlay design method with three indexes,which bases on th ecomparison and analysis of the existing design methods for asphalt overlay at homeand abroad. The three indexes includes: The load stress and temperature stress of oldcement concrete pavement; the maximum tensile stress at the end of asphalt overlay; The maximum shear stress.