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.
Performance-based specifications for pavements
Pavement represent a very substantial portion of the public's investment in infrastructure. It is essential that this investment be preserved through cost-effective planning, design, and maintenance. One way of achieving this is through the use of long-term performance-based specifications. This paper describes the current practice for pavement specification. For the most part, these specifications are "recipe" orientated. Very specific requirements are set for procedures, such as compaction, or as constructed properties such as density. With the proposed system, the contractor would be required to warranty the actural performance of the pavement over an extended term. The paper describes the overall scope of the system, its key elements and advantages, and the major risk factors. As well, the measures that can be used to characterize performance and a model for estimating performance are identified. A stochastic formulation of the model is used to present a method of determining the risk to the contractor based on a design example. Finally, the paper explores some of the concerns associated with the implementation of the system and how these concerns might be addressed. (A)
METHODS FOR PREDICTING MODULI AND FATIGUE LAWS OF BITUMINOUS ROAD MIXES UNDER REPEATED BENDING
The use of modern pavement design methods to prevent cracking necessitates, among other things, determining the moduli and fatigue laws in bending of the bituminous road mixes (base courses and wearing courses). These determinations are now possible, but they involve sophisticated experiments that are not well adapted to pratical purposes. The objective of this paper is to present an original contribution to the prediction of moduli and fatigue laws in sinusoidal bending (controlled stress tests) of bituminous mixes. The results obtained with a large variety of mixes having different bitumen, composition, and size distribution of the aggregates show that this prediction requires only the knowledge of the volumetric composition of the mix (aggregate volume content, bitumen volume content, and void content) and the knowledge of some characteristics of the bitumen used (asphaltene content and penetration). On the basis of the experimental results obtained, general formulas are presented to permit the prediction of the moduli and the fatigue law of a mix. Practical criteria for the selection of the bitumen are also proposed.