Research Of Semi-rigid Base With Asphalt Pavement On Fatigue And Damage Properties

Semi-rigid base with asphalt-pavement, which has good mechanical properties and driving comfort, has become a major style of road structure now. The glass fiber geogrid,with stronge tensile strength, high modulus of elasticity, low coefficient of thermal expansion, wear resistance, slitting-resistant high strength, and good dissolvability in asphalt mixture is widely used in such roads as a major reinforcing material. But related systemic, mature research has not been found. Most high-grade highways are constructed with Semi-rigid base with asphalt-pavement and asphalt concrete pavement in China. As the increasing of traffic volume and heavier vehicles, the semi-rigid under repeated loading show brittle behavior and poor resistance to deformation,which lead to the semi-rigid base with asphalt concrete pavement cracking before meeting the designing life. Cracks in the roads not only affecting road aesthetics, traffic comfort, but also reducing the road formation, weakening the overall strength of the road, increasing maintenance costs.The main reason of cracking is that:the semi-rigid base is under repeated loading,the mechanical properties are getting weaker,and it cracks eventually,as the repeated loading continue,the crack will propagate in the direction vertical to the road surface,which come into being reflecting crack,and the stess concentrating is getting more and more obvious at the top of the crack,also the underside of road pavement,then the road pavement craks finally.With regard to studies on the problems above, classical theories of Fracture Mechanical and the Fatigue Fracture Mechanical are being applied, large numbers of valuable results were obtained,many important problems such as the distribution of the stress and strain near the cracks within the road base or pavement,the rule of crack propagation and the expression of break criterion can be solved by these theories,which are almost about existent macroscopical cracks.However,a vital limitation is inevitably with it,that is these theories can not tell or explain rules of the getting worse of materials'mechanical properties,as well with those phenomenons under the fatigue loading,for this reason, the Damage Mechanics is being naturally used. the damage mechanics, which is based on Thermodynamic, Continuum Mechanics,can be used to analyse rules of the getting worse of materials'mechanical properties under the fatigue loading,by means of Metal Physics, Phenomenology and Probability statistics,among which,the Phenomenology is applied much more widely,and can be effectively used in many plastical and brittle materials besides the metals.Considering these practical problems exist in road engineering,and the limitation of classical theories of Fracture Mechanical and the Fatigue Fracture Mechanical, large numbers of beams composed of semi-rigid base as well with asphalt-pavement were made,and also the static and fatigue experiments were done by means of four points bending loading.The influence that to reinforce road with glass-fiber geogrid to road structure and phenomenons appear in fatigue course are analysed in this paper. Expressly,by using Damage Mechanics Phenomenology theory, the rules of the getting worse of semi-rigid base materials'mechanical properties before macroscopical cracks appearing are explored and studied, furthermore, effective fatigue damage and fatigue life forecasting models with reliability degree are constructed properly,and they can offer practically valuable gists and referrences.