This paper presents the results of a laboratory investigation where an evaluation is made of the PRD (Percentage refusal density) test as a method of control for compaction. It also discusses the use of the Leeds Design Method (LDM) for the determination of the optimum binder content of dense bitumen macadam and heavy duty macadam and for controlling compaction by a modified PRD method. The main conclusions are: (1) The PRD method, although time consuming and laborious, proved to give repeatable results. Because it is not sensitive to changes in binder content it can be used with advantage during the initial stages of a contract to establish target densities which can be checked with nuclear density meters; (2) High PRD values do not necessarily indicate low porosity or low VMA (Volume of voids in the mineral aggregate framework) values. Large changes in porosity are not reflected in the corresponding changes of PRD, therefore control of porosity is still a more reliable method to assess the long term properties of bituminous macadams; (3) The relation between dynamic stiffness and porosity can be expressed by an exponential decay function which is statistically valid. The constants of the function are influenced by binder viscosity and mode of compaction; (4) Reduction of porosity by increased compaction, use of higher viscosity binders and larger quantities of filler lead to large improvements in the value of dynamic stiffness; (5) The Leeds Design Method is adequate for the laboratory design of dense bitumen macadams. The optimum binder contents obtained correspond to the upper values given in the specification. The LDM should be modified to allow design of mixes containing aggregate size particles up to 28 mm diameter; (6) The results of the LDM design have shown that it will be necessary to assign adequate values of stability, flow and porosity to obtain the optimum binder contents (OBC).(A)

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    LONDON,   United Kingdom  WC1H 0DZ
  • Authors:
    • CABRERA, J G
    • RIDLEY, A
    • Fekpe, E
  • Publication Date: 1990-7


  • English

Media Info

  • Pagination: p. 27-
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00606719
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS, ATRI
  • Created Date: Mar 31 1991 12:00AM