Insa Franco, R.; Hidalgo Signes, C.; Martínez Fernández, P.; Medel Perallon, E. (2015). Characterisation of an unbound granular mixture with waste tyre rubber for subballast layers. Materials and Structures. 48(12):3847-3861. doi:10.1617/s11527-014-0443-z. Abstract. Scrap tyres are a solid waste material produced in large quantities. One potential way of disposal is to use rubber particles from shredded tyres as a construction material. Within this context, this paper presents a comprehensive set of laboratory and field tests carried out to evaluate the characteristics of coarse aggregates mixed with rubber particle. The main objective is to assess whether these mixes could be used to form the subballast layer in new railway lines. All the technical features usually required for subballast were tested, including degradation, bearing capacity, density, resilient modulus, etc. The results show that adding between 1 and 10% of rubber (in weight) improves resistance to degradation. On the other hand, bearing capacity is reduced, but still well over the usual range for common subballast if the rubber content is limited to less than 5%. Moreover, the extension and compaction of these mixes can be done using conventional construction equipment. 1 CHARACTERISATION OF AN UNBOUND GRANULAR MIXTURE WITH WASTE TYRE RUBBER FOR SUBBALLAST LAYERS

This paper focuses on the assessment of the vibration behaviour of granular subballast materials mixed with rubber particles from scrap tyres. The main objective is to evaluate whether these mixes attenuate vibrations caused by passing trains, and if so, to what extent. Several laboratory and field tests were carried out to monitor the response of such materials to various excitation sources. The results show that under controlled laboratory conditions, the addition of rubber (up to 5% by weight) greatly increases the damping ratio and reduces vibration. Field tests also show that higher percentages of rubber yield a significant alleviation of vibration caused by repetitive and harmonic loads that are similar to those produced by passing trains. An addition of 5% by weight yields a reduction of 50% in the mean acceleration peak at one metre from the excitation source. The anisotropy of the mix is another key factor when evaluating the vibration behaviour of these mixes.