A FEM Modeling of the Concrete Pavement Made of the Recycling Material

Paper is a brief review of the research focused on formulation an numerical model for the concrete pavement which is made by the recycling material. For numerical modeling the finite element model (FEM) and the 3D finite element model were applied. The software EverFE 2.25, was used. The results of FEM analysis is in a chapter shape showing move value change, strees and deflections for all layers a construction road model. In the next phase of the research was provided by FEM software with appropriate general purpose non-linear models, which allows the analysis of the real behavior of solid pavement under load.


Introduction
The concrete pavement consists of four layers, including a subgrade.The first layer is concrete pavement, the second layer is made of crushed stone with fraction 0/31.5, and third layer is made of crushed stone 0/63.Each layer takes over the load and transmits it to the subgrade.The goal of this study is to find out maximal/minimal principal stress values per slab.We used a bus, very frequent on that section of the road.The model is carried out with the software EverFE 2.25 which gives us the model results with 3D FE element [1][2][3][4][5][6][7][8][9][10][11].

3D fe analaysis
To model a stress notation of the special systems 3D solid FE are used as the most complex and ensure the most precise approximation.Applying these FE we get models with high degree of freedom, therefore their application is limited to analysis of specific construction systems [1].
The software Ever FE version 2.25, has been used for modeling.The software is equipped with the qualitative tools for creating 3D FE models.The first step in creating a model of the concrete pavement is to determine its dimensions and to define the number of layers.Each layer has a specific modulus of elasticity (E), Poisson`s ratio (ν) and layer thickness (d) [2].All the values are presented in Table 1.Ever FE is equipped to allow the user to specify a wide range of realistic loads that may be applied to a solid pavement through a vehicle's tire.
The first step in selecting a load is to choose the type of tire contact which can be rectangular or circular.After selecting the type of tire contact, the user must define the rest of the load parameters.The wheel type can be selected as single or dual.The axle type can be selected as single or tandem.
The test bus station has tree concrete pavements that are made of recycling material and they have 15 dowels.The dowels durations are 600mm and diameters are 22mm.For testing load was used the bus which has 120kN on front axle and 120kN on rear axle (Fig 1, 2).

Research results and discussion
After defining the parameters the above menitoned, the research results are obtained.EverFE allows the results of the finite-element analysis to be presented using any of four options available from the visualization menu: Stresses (Maximal Principal, Minimal Principal, Stresses in the x-x plane, y-y plane, z-z plane, x-y plane, y-z plane and z-x plane), Displacements, Results for Points, and Results for Dowels [2].
Displaced shapes of slabs and the base layer can be viewed for any project for which a solution exists.The results for this points are showing the maximum and minimum principal stresses and their locations in the corresponding slab; the red text show the highest principal stress on the slab.
Selecting dowels from the Visualize menu show all moments for any selected dowel.The five force components that can be viewed: Nq (axial force), the shears Fr and Fs, and the moments Mr and Ms.The subscripts q, r and s refer to the dowel local coordinate system, and correspond to the global model (x,y,z) axes [2].The maximum values of shear and moment are displayed for the currently selected dowel at the bottom of the dowel results panel.These maximum values are computed as the magnitude of the "r" and "s" components, which is appropriate for a dowel with a circular cross-section.The following charts present the characteristic cross-sections of the stresses, displacements, results for points and results for dowels.(Fig. 3) The maximal principal stress is in the center concrete pavement, so the major impact is noticeable in the upper layers (Fig. 4).The maximal stress is in the center of middle concrete pavement, and the minimum is in the end of the first pavement and the start of the third pavement (Fig. 6, 7).The maximal stress is in the all slabs, but the minimum is under the wheels.All slabs are deflected, even thought the loads are placed on first and third slab, because it has dowels that link all slabs and loads.The numbers in each rectangle shows the maximum and minimum principal stresses and their locations in the corresponding slab; the red text show the highest principal stress on the slab (Table .2).The bold text values maximal moments both on first and second slabs and second and third slabs.Fig. 9-12.Between second and third concrete pavement there are big leaps for Shear Forces (Fr).Between second and third concrete pavement there are big leaps for Shear Forces (Fs).Between second and third concrete pavement there are big leaps for Moment (Mr).

Conclusion
After the research was carried out, we have got the results in the form of a model and graphics which ensure an insight in all their changes and deviations.The conclusions of the study are following: x there are substantial deviations in the stresses, displacement and results for dowels.The cause of these changes is the traffic loading, x the loads are changeable in all three concrete pavements.
x The direction of further research: x test influence to use reinforce concrete pavement, x testing joints with the big diameter at the ends of the concrete pavement, x test influence with angle on the first and the final pavement.

Fig. 4 .Fig. 5 .
Fig. 4. Minimal Principal.The minimal principal stress is in the end of the first pavement and the start of the third pavement.(Fig.5)

Fig. 7 .
Fig. 7. Deflections of the all slabs and the base.

Fig. 9 . 3 Fig. 10 .
Fig. 9. Axial Forces (Nq).They have an upward linear dependence on the end of second pavement and another linear decreasing dependence at the beginning of third pavement.

Table 1 .
Pavement structure with characteristic data

Table 2 .
Maximal moment and maximal shear for dowels