Characterisation and Evaluation of Marginal Basecourse Aggregates and the Performance Improvement with Stabilisers

Abstract

The importance of marginal materials in reducing road construction costs has been realised by road agencies around the world. However, utilising marginal materials without any treatment in the road base can still cause rutting and shear failure of the pavement due to their defects in mechanical, chemical and geological properties. Consequently, to make better use of marginal basecourse materials, two objectives are made in this research: Understanding the ‘the marginal’ component of aggregates and improving the performance of the marginal aggregates by targeting the reason for marginality. Five greywacke aggregates were studied in this research. The testing methodology is designed to understand the marginality of materials and evaluate the stabilisation techniques. These aggregates have been tested according to the local standard New Zealand Transport Agency (NZTA) M4 specification and assigned to either premium or marginal aggregate categories. To better understand the ‘marginality’ of aggregates, the mineralogical composition of all aggregates was determined using geological testing methods. A one-dimensional swelling test was developed to determine the effect of swelling minerals on the performance of the water-saturated aggregates. The stress-strain behaviour of unbound granular aggregates was investigated using repeated load triaxial (RLT) tests under soaked and drained conditions. Lime and cement were used to treat marginal materials. The stress-strain behaviour of stabilised marginal materials was investigated under a soaked condition. The results show that the mineralogical and geological characteristics of granular materials have a great impact on the mechanical performance of these materials. Sufficient detrimental minerals, particularly swelling clay minerals, contained in a material will result in the material transforming into a marginal or unacceptable material, particularly when in contact with water. It is insufficient to evaluate the quality of the materials by only using a ‘pass/fail’ categorisation of engineering tests (specified by local standards). Further infrequently used testing methods (e.g. XRD, the swelling test and RLT test) are required, alongside standard test performance measures, carried out in the context of the intended aggregate loading/environment. Cement and lime stabilisation both improve the mechanical behaviour of marginal aggregate 2 under soaked conditions. However, cement stabilisation is more effective than the lime stabilisation.