Computer Simulation of Low Volume Roads Made from Recycled Materials
— Low volume roads are widely used all over the world. To improve their quality the computer simulation of their behavior is proposed. The FEM model enables to determine stress and displacement conditions in the pavement and/or also in the particular material layers. Different variants of pavement layers, material used, humidity as well as loading conditions can be studied. Among others, the input information about material properties of individual layers made from recycled materials is crucial for obtaining results as exact as possible. For this purpose the cyclic-load triaxial test machine testing of cyclic-load performance of materials is a promising test method. The test is able to simulate the real traffic loading on particular materials taking into account the changes in the horizontal stress conditions produced in particular layers by crossings of vehicles. Also the test specimen can be prepared with different amount of water. Thus modulus of elasticity (Young modulus) of different materials including recycled ones can be measured under the different conditions of horizontal and vertical stresses as well as under the different humidity conditions. Using the proposed testing procedure the modulus of elasticity of recycled materials used in the newly built low volume road is obtained under different stress and humidity conditions set to standard, dry and fully saturated level. Obtained values of modulus of elasticity are used in FEA.
Sensitivity Analysis of Principal Stresses in Concrete Slab of Rigid Pavement Made From Recycled Materials
: Complex sensitivity analysis of stresses in a concrete slab of the real type of rigid pavement made from recycled materials is performed. The computational model of the pavement is designed as a spatial (3D) model, is based on a nonlinear variant of the finite element method that respects the structural nonlinearity, enables to model different arrangements of joints, and the entire model can be loaded by the thermal load. Interaction of adjacent slabs in joints and contact of the slab and the subsequent layer are modeled with the help of special contact elements. Four concrete slabs separated by transverse and longitudinal joints and the additional structural layers and soil to the depth of about 3m are modeled. The thickness of individual layers, physical and mechanical properties of materials, characteristics of joints, and the temperature of the upper and lower surface of slabs are supposed to be random variables. The modern simulation technique Updated Latin Hypercube Sampling with 20 simulations is used. For sensitivity analysis the sensitivity coefficient based on the Spearman rank correlation coefficient is utilized. As a result, the estimates of influence of random variability of individual input variables on the random variability of principal stresses s1 and s3 in 53 points on the upper and lower surface of the concrete slabs are obtained.
Influence of Aggregate Gradation and Particle Shape/Texture on Permanent Deformation of Hot Mix Asphalt Pavements.
Abstract : In recent years, the incidence of premature rutting in hot mix asphalt (HMA) pavements has increased. This deformation usually develops in the wheelpaths under channelized traffic in the top 3 to 4 in. of the HMA pavement. The primary cause of this premature rutting has been higher traffic volumes, increased loads and tire pressures, and lower quality HMA mixtures. This investigation focused on permanent deformation produced by plastic flow and densification of the HMA layers. Approximately 85 percent of the total volume of HMA mixtures is aggregate, and the performance of HMA mixtures is greatly influenced by aggregate properties. This study was conducted to evaluate the influence of these properties on permanent deformation characteristics of HMA mixtures. The analysis consisted of correlating aggregate properties with HMA mixture properties and the rutting potential of HMA pavements. The research study consisted of a literature review, laboratory evaluation, and field evaluation. The laboratory evaluation consisted of aggregate characterization tests and HMA mixture tests. The aggregate characterization tests included Particle Index, National Aggregate Association (NAA), and Modified NAA particle shape and texture, unit weight and voids in aggregates, and direct shear tests. The HMA mixtures were evaluated with Marshall properties, Gyratory Testing Machine, indirect tensile tests, direct shear tests, and confined repeated load deformation tests. The field evaluation included construction of 10 test items, trafficking with a load cart simulating aircraft loads and tire pressures, and evaluating performance with rut depth measurements. (MM)