The resistance to fatigue of dry asphalt rubber concrete for sub-ballast layer

Resumo

This study presents a description of laboratory evaluation of hot mix asphalt using recycled crumb rubber as an additive modifier to describe the performance of asphalt rubber compare to a conventional mixture. The improvement of the mechanical performance of the ballasted rail track due to the to sub-ballast layer has been known for a long time. Its bending behaviour decreases the tensile strain, the damage of fatigue process, and reduces the maintenance costs. New techniques for recycling discarded tires are being investigated. Finely ground rubber particles appear to be a promising option. The use of crumb rubber allows greater sustainable resource through the decrease of the ground borne vibration. The environmental impact can be reduced using the Dry process method, in which an amount of 1-5% of scrap tire rubber pieces of cars and lorries, is mixed with aggregates during heating process before the mixture is introduced into asphalt binder, and subsequent compaction. The objective of this experimental survey was to determine the influence of the rubber content, the load frequency and the temperature on the mechanical properties for the sub-ballast. Rubber pieces function as elastic aggregates imparting greater flexibility to the bituminous slab. Therefore, it is a material whose properties may be affected due other factors such as source, grinding procedure, tire type and even on the particular batch. A Laboratory research based on the 4-point-bending test for fatigue and Marshall test for binder content, was carried out to measure the stiffness modulus of: First mix, a conventional no rubber hot mix asphalt, according to the Italian standard; Then, two bituminous mixtures with different rubber content between 1-2% of rubber, Finally, a generic type of Rubberized binder mixture with 3.5% rubber content by weight of the aggregates. Chemical requirements for scrap tire rubber eliminate unsuitable sources, to provide only High Natural Rubber, which is more suitable or adequate for mixing with the asphalt concrete, improving resilience of binder and increasing fatigue resistance.