Effect of mother rock strength on rubber-coated ballast (RCB) deterioration

Abstract

Applying traffic load to railway tracks as well as tamping operations results in ballast deterioration. To tackle this problem, several solutions have been proposed in the literature. One of the technics presented in recent years to improve the behavior of this layer is to cover ballast aggregates with rubber particles. However, the application of this method for ballast with different strength levels has not been studied so far. Moreover, using a mix of rubber and adhesive to glue rubber particles to the ballast aggregate has not been investigated. This paper has investigated the effect of mother rock Unconfined Compressive Strength (UCS) on the deterioration of rubber-coated ballast (RCB) and RCB preparing methods. With this aim, first, the optimal method of coating the ballast aggregates focusing on selecting the appropriate percentage of rubber particles mixed with adhesive has been evaluated by Los Angeles test and Minitab analysis and appraised by scanning electron microscopy (SEM) images. Then, by applying selected rubber coating on ballast aggregates of Shahriyar, Anjilavand, and Koohin quarries located in Iran, the effect of aggregates’ properties on the abrasion behavior of RCB has been considered through Los Angeles and Micro-Deval experiments. In the next step, breakage, settlement, stiffness, and damping ratio of ballast taken from all three quarries, with and without rubber coating, have been studied by performing the ballast box test by applying the load amplitude of 15 kN with the frequency of 3 Hz up to 100,000 cycles. The results illustrate that the optimal method was to make RCB samples with polyurethane-based adhesive model ADH-2535 mixed with 15% rubber particles. Furthermore, the application of rubber coating caused an average reduction of 72.11% in the Los Angeles abrasion (LAA) and 92.6% in Micro-Deval abrasion (MDA). In addition, the breakage of RCB under cyclic loading has been reduced by 89% in all three samples. While the short-term settlement of RCB samples compared to uncoated ballast increased 29% on average, its settlement decreased in the long-term, and it was more substantial in ballast with lower UCS. Although the damping ratio in samples with rubber coating was almost twice the damping ratio of uncoated ballast, the stiffness of the RCB samples has been reduced by 53%. This reduction has been independent of the type of mother rock. Overall, the construction of RCB with softer ballast proved to yield the best results.