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IMPROVED ROAD BASES FOR LONGER PAVEMENT LIFE --BITUMEN, FLEXIBLE AND DURABLE. 3RD EUROBITUME SYMPOSIUM 1985, THE HAGUE, NETHERLANDS, SEPTEMBER 11-13, 1985

A bituminous road base must have the correct balance of mechanical properties in order to provide good performance in the road economically. The properties of importance are elastic stiffness (for good load spreading), fatigue resistance (to prevent cracking) and resistance to permanent deformation (to minimise rutting). Present British standard materials for road bases are either gap graded hot rolled asphalt (hra) or continuously graded dense bitumen macadam (dbm). Both materials are specified by use of recipes which are the result of empirical developments. The hra is a relatively rich material with good stiffness and fatigue resistance but a tendency to deform. The dbm offers good resistance to permanent deformation, has reasonable stiffness but, being of low binder content, offers low resistance to fatigue cracking. Extensive laboratory testing on cores of a wide range of road base mixes embracing these two generic types together with modification to them, resulted in the development of mixes with a better balance of the desirable mechanical properties. The hra was modified by reducing its binder content and introducing more filler. The dbm was modified by including a larger quantity of a harder grade of binder. Details of the measured mechanical properties are given showing increased elastic stiffness and fatigue resistance for the modified dbm, while the modified hra has improved deformation resistance. Compactibility of the various mixes was also studied showing that the modified materials were practicable. Full scale trials with these modified materials were conducted to ensure that they could be manufactured, laid and compacted under normal conditions. The trials were designed using the analytical techniques for pavements developed at Nottingham and these, together with other computations, demonstrated that longer lives can be achieved with the same layer thicknesses. Alternatively, significant reductions in thickness may be specified for equivalent life. The relative deformation resistances of the four types of mix, two standard and two modified were used to develop improved criteria for pavement design calculations using an analytical procedure. The result was expressed in terms of a "rut factor" used in conjunction with the well-known "subgrade strain" criterion for design against excessive rutting. The work described in this paper links materials properties to design computations in order to emphasise this important interaction. The material modifications are intended as a first step towards the development of a design method for bituminous road base mixes which will allow locally available materials to be economically utilised.(a) for the covering abstract of the symposium see IRRD 815173.

  • Corporate Authors:

    EUROBITUME

    BD EMILE BOCKSTAEL 351
    Bruxelles, ZZ Belgique   
  • Authors:
    • BROWN, S F
    • Cooper, F E
    • Pooley, G R
  • Publication Date: 1985

Language

  • Undetermined

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Filing Info

  • Accession Number: 00482094
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Apr 30 1989 12:00AM