Material testing for sustainable pavement foundation design

The current UK pavement foundation design process is based upon the California bearing ratio, coupled with a ‘method’ specification based on past experience and proven performance. This provides an empirical indicator of adequate performance but limits the use of materials. This in turn restricts the wider use of marginal and recycled/secondary aggregates necessary to achieve sustainability targets. Additionally there is a move towards analytically based pavement design, based upon the fundamental material performance properties of elastic stiffness and shear strength. Analytical design, combined with ‘performance’ specifications, potentially allows any materials that are ‘fit for purpose’. This approach requires field measurements to confirm that the assumed design performance is achieved; performance data for design are required before the materials are used to ensure confidence in their likely behaviour. A large-scale laboratory assessment test has been developed to measure the performance of coarse granular (capping) materials. The test utilises devices proposed to measure/check performance in the field, thus providing directly comparable results. This paper discusses the development of the laboratory performance test, its use and role in the wider context of the design process, and suggests areas where this test can help foster sustainable use of materials.