Evaluation of limestone aggregates for railway ballast: particle characteristics and shear strength analysis

The West-East Integration Railway (Ferrovia de Integração Oeste-Leste -FIOL) is an infrastructure project designed to integrate and promote the socio-economic development of the Northeast region of Brazil. In countries with heavy-haul railway operations, there has been increased demand for ballast materials that can withstand cyclic loading of up to 40 tons per axle. In this context, in order to achieve greatest operational efficiency, it is essential to evaluate the characteristics of the limestone aggregate to be used in the ballast layer, as well as the level of cyclic stress that the ballast can withstand. The laboratory investigation consisted of characterization tests, single particle crushing tests, monotonic triaxial tests, and evaluation of the morphological properties of the particles using the Aggregate Image Measurement System. This paper introduces the equipment, describes the experimental procedures, outlines the specimen preparation, and presents the experimental results. The purpose of the study is to estimate the long-term behavior of ballast based on monotonic triaxial tests, the shakedown phenomenon, and the cyclic stress ratio. The results suggest that the cyclic stresses commonly observed in heavy-haul railways may exceed the cyclic stress ratio compatible with the shakedown regime, resulting in a progressive plastic creep regime. Furthermore, the quantity of non-cubic particles exceeds the limits set forth in international ballast standards necessitating a rigorous assessment of the particle shape prior to use in the field.