The paper describes the accepted understanding of the shakedown concept. The results of several repeated load triaxial tests performed on crushed rock aggregates at different stress levels for a large number of repetitions of loading are given. The development of the resulting permanent deformation which accumulates with the repeated loading is depicted and compared with the types of responses usually described by the shakedown approach. It is shown that the existing shakedown approach can represent some, but not all, of the observed responses. Thus a modified set of possible responses is defined in shakedown terms and some explanation of the differences from the conventional approach are given. It is concluded that the method of description could give a powerful material assessment and pavement design tool for the engineering of unbound pavement bases. A design chart is derived from the data described, so as to illustrate a possible design approach.