An assessment of the relationship between the petrographic, physical, and morphological properties of aggregates used for railway ballast

The performance of the ballasted permanent track is linked to the quality of the aggregates that make up the ballast layer. This layer is the only one that allows the regularization and leveling of the rail pavement. Evaluating the relationships between the properties of rocks and aggregates helps in predicting the behavior of rail ballast and in reducing wear and premature failures in the permanent way. The objective of this study is to evaluate the relationship between the petrographic, physical and morphological properties of the aggregates. The materials were selected from the literature with application of rocks for different areas. The petrographic properties of the rocks were filtered or identified through photomicrographs. The physical and/or morphological tests of the rocks were verified. Based on the database of 21 rocks, the results show the strong influence of grain shape, granulation, texture, contact between minerals and, mainly, mineralogy on the physical and morphological behavior of the aggregates. Rocks with higher mafic content provide greater resistance to aggregate degradation. Rocks with higher mafic and biotite contents contribute to increase the angularity value of aggregates after Micro-Deval (MD) wear tests. Medium/coarse grained rocks induce a higher value of unfilled intergrain microcracks between minerals and, consequently, higher porosity and water absorption and higher compression degradation. Furthermore, the results show that it is possible to predict the morphological behavior of aggregates after degradation from the morphological variables before their degradation.

Automated summary

This study evaluates the relationship between the petrographic, physical, and morphological properties of aggregates in ballasted permanent track. The results show that properties such as grain shape, texture, and mineralogy strongly influence the behavior of the aggregates. Higher mafic content in rocks leads to greater resistance to aggregate degradation, while higher mafic and biotite contents contribute to an increase in angularity value after wear tests. Medium/coarse grained rocks induce higher porosity, water absorption, and compression degradation.