Proof of the effectiveness of asphalt reinforcement and evaluation of the applicability into an existing design method
The service life of asphalt pavements depends on various factors according to the current standard design methods. The material characteristics, layer thicknesses, climatic conditions and the in-tensity of the traffic load are the most decisive factors that influence the dimension of asphalt pavements. Based on this, various proofs of calculation methods are developed in accordance with the fatigue charac-teristics and rutting depth behavior of the asphalt as well as deformations of the substructure. Despite the positive experience obtained from globally increasing construction sites over the last 40 years and from the extensive and successful research projects, the asphalt reinforcement has unfortunately not been suffi-ciently taken into account in the design of asphalt pavements. Different design approaches are established based on controlling the horizontal movements induced as a result of dynamic stresses in the form of re-tardation or in many cases to prevent (restrict) propagation of reflective cracks in recently constructed lay-ers. In addition, studies have shown that reduction of the strain in the area of the tensile zone (e.g. bottom of asphalt layer) significantly increases the durability of the pavement and the service life of the project. Accordingly, this research aims at numerical investigation of the mechanical behavior of the reinforced asphalt layers in terms of deformation and stress distribution in the pavements. Within this framework, a series of numerical finite element calculations will be conducted to study the factors those contribute to reduce the fatigue behavior of the reinforced asphalt pavements in terms of service life or the permissible loads.
A number of FEM calculations carried out to evaluate the effect of the bonding between the asphalt rein-forcement on the distribution of the stress and strain in the pavement structure. Different bonding is at-tributed to the type of the geosynthetic layer (e.g. nonwoven or grid), type of the raw material in terms of flexibility and stiffness (e.g. polyethylene, polypropylene, polyester) and the size of the apparatus for grids (e.g. 20×20 mm or 40×40 mm). Based on the analyses conducted in present study, the following conclu-sions can be drawn:
• A significant improvement in pavement behavior is obtained by applying of reinforcement grid with larger aperture size of 40×40 mm in the tension zone at the bottom of the surface asphalt layer. The horizontal strains are significantly lower compared to unreinforced pavement system, pavement with nonwoven stress absorbing layer and pavement reinforced with geogrid with improper interlocking.
• Using the nonwoven geotextile as stress absorbing membrane instead of reinforcement grid restricts proper interlocking between the asphalt layers and allows higher strains in the contact area. This can have a negative effect on the necessary required bonding (risk of slippage effect) and thus on the dura-bility of the asphalt pavement system (decrease of the service life).
• The reduction of the strain at the bottom of the surface asphalt layer strongly depends on the type of the asphalt reinforcement grid and its apparatus size. The strain at the bottom of the asphalt layer becomes less than 1 when the geogrid is used to reinforce the pavement while it becomes minimum when the asphalt geogrid made of polyester polymer with proper interaction flexibility and larger size of appa-ratus is used to reinforce the pavement.
• The use of the asphalt reinforcement should minimize the deviation of the stress and strain at the bot-tom of the asphalt surface layer and the top of the base course asphalt. Thus the system performs more uniformly and reduces the risk of the slippage between the layers and also the reflection of the cracks from base course to the surface.