Numerical determination for optimal location of sub-track asphalt layer in high-speed rails

Well-graded asphalt mix with the merits of high sound absorption, low water permeability, excellent strength, and easy construction is an important option for high-speed railway substructures. On the basis of finite element method, a model with conventional ballasted trackbed （To） and four ballasted trackbeds models with different positions of asphalt layer were analyzed, in which 15 cm thick asphalt layer was used to replace the different sub-track layers, the bottom and the top of upper subgrade and of ballasted trackbed, named as Tb T2, T3, and T4, respectively. The results showed that the range of peak vertical accelerations on the top of subgrade surface of T2 and T4 were smaller than T1 and T3; T1 and T2 perform better in decreasing the maximum vertical deformation of subgrade than T3 and T4; the maximum transversal tensile strain of T4 is almost twice than the other three. The trackbed bears more stress when the asphalt layer is located at the lower part of railway trackbed.

Procedure for a Temperature-Traffic Model onRubberized Asphalt Layers for Roads and Railways

The impact of temperature on the mechanical properties and thermal susceptibility of the railway bituminous sub-ballastlayer, has served as motivation to develop the advanced measurement of thermal cycles in this layer and, an evaluation of the averageseasonal temperatures interpolated by sinusoidal functions, of which characteristic parameters are determined. According to weathersituation, Barber＇s temperature model was used to prove the effectiveness for the railway superstructure. It is included the assessmentof improved modified asphalt mixes performed with coarse rubber from scrap tires, having 1.5 to 3 percent of crumb rubber （particlesize 0.2-4 mm） by weight of the total mix, as sub-ballast layer in railway and base layers on roads, recurring to the Superpave mixdesign compaction enhanced after computer simulations to evaluate real stresses derived from the rail traffic and climatic conditions.This article following the assessment of the average seasonal temperatures, involves the characterization of rubberized materials withattention to crumb rubber properties, designed with dry technology, to enhance the bitumen-rubber and binder-voids ratios. Indirecttensile strength and water sensitivity tests were applied for the evaluation of its mechanical properties including dynamic complexmodulus at elevated temperature to measure the amount of bitumen absorbed by the rubber. The rubberized mix-results obtained andthe comparison with a conventional HMA （hot mix asphalt） show that these dry rubber bituminous mixtures are particularly effective indamping vibrations. The purpose of using rubber modifiers in hot mix asphalt to obtain a stiffer-elastic sustainable material has beenachieved for the assessment of its behavior in sub-ballast/base layers.