Testing of Unbound Materials in the Nottingham Asphalt Tester Springbox (05-0282)
Paul Edwards, Scott Wilson Pavement Engineering Ltd., United Kingdom
Nick Howard Thom, University of Nottingham, United Kingdom
Paul Richard Fleming, Loughborough University, United Kingdom
John Williams, Highways Agency, United Kingdom

The current trend in mechanistic (analytical) pavement design is to use the mechanistic properties of pavement materials. This is compatible with the move towards performance-based specifications, away from traditional empirical-based design methods and recipe specifications. Other drivers such as the European wide adoption of aggregate mixture standards, which no longer differentiate on source, and moves towards sustainable construction mean that a wide range of recycled, secondary and primary aggregate sources can potentially be utilized within highway construction. The requirement for accelerated, performance-based testing is therefore coming to the fore. The Highways Agency (UK) has funded an accelerated testing programme across a range of unbound capping and subbase materials. The performance parameters assessed, over a range of moisture/soaking conditions, are resistance to permanent deformation and resilient stiffness. The apparatus used during the unbound mixture assessments is the newly developed Springbox, which utilizes the standard Nottingham Asphalt Tester (NAT) loading frame and software. This follows a simplification of the K-mould test and facilitates repeated loading of 170mm cubic specimens under variable confinement. Samples are compacted into stainless steel liners. If required, samples can then be soaked prior to placement within the Springbox apparatus for testing. This paper discusses the aggregate mixture performance parameters being measured, briefly outlines sample preparation procedures, introduces the Springbox equipment and test procedures, describes a testing program of unbound capping and subbase materials, and presents results. The performance of the Springbox apparatus is discussed and conclusions on the relative performance of the aggregates are presented.