Assessment of secondary materials for pavement construction: Technical and environmental aspects

Current research at the University of Nottingham to enable the use of secondary materials in road construction covers technical aspects, mechanical properties of waste materials and the environmental implications of their use. Materials studied are minestone, china clay sand, slate waste, pulverised fuel ash and furnace bottom ash. The laboratory programme set up for this research and the methodologies suggested for the study of the properties of these materials are presented. The test methods currently used to select pavement aggregates are presented along with current methods for the assessment of the environmental impact of secondary aggregates. The potential of the secondary aggregates is assessed within the current technical and environmental procedures previously presented. Two new methodologies are presented, one for the mechanical examination of secondary aggregates and one for the environmental assessment. The mechanical assessment encompasses conventional characterisation and classification tests on both unbound and lightly treated pavement materials, and fundamental tests such as repeated load triaxial tests (RLTT) and repeated load indirect tensile tests (RLITT). Some sample results are presented, suggesting the feasibility and adequacy of this methodology for material discrimination, and evaluation of mechanical properties for design purposes. The environmental assessment indicates how the leaching concentration of contaminants from intensive testing can be used as the first step in assessing the environmental acceptability of a secondary material, and the means of determining a more realistic measure of in situ performance is discussed. The advantages and advancements of the presented methodologies over the basic and inappropriate techniques currently used to assess the suitability of secondary aggregates for use as pavement construction materials are discussed.