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Development of an alternative maintenance technique for railway ballasted tracks

2. Methodology

2.1 Materials

In order to analyse the effect of using rubber particles as flexible aggregates during stone-
blowing process (mixed with part of natural aggregates used in such conventional technique),
these elastic components were obtained by grinding up waste tires primarily composed of ru-
bber (Figure 1). The density of the rubber particles was around 1.15 Mg/m3. The gradation of
the elastic granules was as follows: 2% of the particles were between 8 and 12 mm; 61% from
12 to 16 mm; 34% from 16 mm to 22.4 mm; and 2% from 22.4 mm to 25 mm. The rationale for
selecting these sizes was to avoid percolation and package (Selig and Waters, 1994; Fair, 2003).
For the same reason, the size of the small natural stones (used to fill the gap between the
sleeper bottom and ballast surface after settlement during stoneblowing process) was mainly
fixed between 14 mm and 20 mm. These stones were obtained from ophitic rocks, presenting a
resistance to fragmentation lower than 8% (EN 1097-2), which is appropriate to limit the fouling
of ballast associated with natural aggregates degradation. In Figure 1, the stones are orange
painted in order to distinguish them from ballast particles.

Figure 1. Main materials used for the solutions analysed in this study.

As reference elastic elements to compare the influence of applying rubber particles under slee-
per, the USPs used in this study (Figure 1) were manufactured from end-of-life deconstructed
tire tread layers (obtained without any need for grinding), which have been shown to be appro-
priate for application as elastic elements in railway tracks (Sol-Sánchez et al., 2014) These pads
were categorized as soft USP (4.5 mm thick) and stiff USP (2.5 mm thick), presenting a static
bearing modulus close to 0.20 N/mm3 and 0.40 N/mm3, respectively.
On the other hand, to carry out this study, a conventional track section was reproduced in
laboratory by using a testing box that allows for simulating the effect of trains passing, and
then, the track settlement due to traffic, which requires maintenance interventions (in this
case stoneblowing without and with the combination of the different elastic solutions – rubber
particles or USPs) to restore initial position. The box dimensions ( 1 m x 1 m, and 500 mm in
height) allowed for the introduction of a piece of concrete sleeper (250 mm in width and 850
mm in length) with a flexible fastening system and a piece of rail type UIC-54 with a length

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