Unbound crushed concrete in high volume roads

A field and laboratory study

Abstract

In Norway, recycled concrete aggregate has recently been introduced in design codes for road construction, including material specifications. A number of field projects have revealed good functional properties (proven suitability), despite the fact that the mechanical properties of the materials in many cases do not comply with specifications concerning mechanical strength. Many traditional test methods for mechanical properties are clearly not suitable for this kind of materials. A proper evaluation should therefore be based on performance-related (functional) tests. The paper discusses these field-lab contradictions with reference to a field trial at highway E6 south of Trondheim. There crushed concrete is used as sub-base layer in a pavement designed for rather heavy traffic (ADT > 10000). Several field and laboratory tests have been conducted before, during and after construction, and the paper is focusing on comparing field tests with both empirical (old) and functional (new) laboratory tests, including a large-scale cyclic triaxial test apparatus. The road was constructed 2003-2004, and will be followed up by frequent bearing capacity (FWD), rutting and evenness (IRI) measurements. These data and results, both from field and laboratory investigations, will give valuable inputs to new Norwegian pavement design standards. This should encourage further use of recycled/secondary materials.