Trials of a performance specification carried out as part of two motorway strengthening contracts are described in which roadbase and basecourse materials were specified in terms of their structural properties. The performance tests examined were the indirect tensile test to measure elastic stiffness and the repeated load axial creep test to determine resistance to deformation; both these tests were carried out using the Nottingham Asphalt Tester (NAT). These trials examined the practicality of a performance specification and the associated test procedures, obtained feedback from the contractors and supervising engineers and identified potential problems to be resolved before a performance specification can be introduced. The study showed that there was a strong link between material composition and elastic stiffness and that the indirect tensile test has the potential to be a good performance test. No such significant link was found between mix composition and creep stiffness measured using the repeated load axial test. Which suggests that this test in its present form is not suitable for contract application. The trials demonstrated that a performance specification will provide an improved quality of material and there are potential benefits for both the Department of Transport and the Contractor. Further performance specification trials are recommended based on approval of a job-mix. (A)

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