Mechanical behavior of natural and recycled granular materials for roads

This paper presents a study on resilient and permanent strains measured with the precision cyclic load triaxial test on a limestone aggregate (reference material) commonly used in subbase or capping layers in Belgium and on two recycled materials (steel slag and crushed concrete aggregate) also used in subbase or capping layers. The influence of stress level, water content, density, and compaction method (vibrating hammer or vibrocompaction) was analyzed. Tests with one cyclic stress level on one specimen (single stage loading) and tests with several cyclic stress levels on the same specimen (multi-stage loading) were performed, in order to evaluate the prediction capability of the multi-stage loading test. The latter test procedure is quicker and more practical. Although the permanent strains obtained by the two test procedures were different, the multi-stage loading method did indicate the trend of the long-term behavior of the material. The test results showed that in comparison with the reference material, the recycled materials, particularly the steel slag, exhibited good mechanical behavior (high stiffness, high strength, and good resistance to permanent strains) under-well controlled conditions of water content