Since the standardization of grain sizes in 1958, the different aggregates are linked together: 0/2 to 2/4, 2/4 to 4/6, etc. definitions and tolerances are linked with the efficacy defined by E.I. Ivers, (the efficacy E equals 100 percent minus Y where Y is the value of equal quantities of retains and passings at a certain theoretical mesh dimension X). E must be equal to or greater than 87.5 percent. The ratio of the quantity which really passes through to the quantity which should have passed through is given by a formula. For the efficacy E there exist only experimental curves, the maximum of which for low rates of screening scarcely exceeds 92 percent doubts are expressed as to the justification of the requirement that E equals 87.5, particularly in the case of random sampling and measurements carried out on badly calierated screens. In practice, it seems that a slight variation in the dimension of an aggregate for a surface carpet entails a specific surface variation markedly below the precision of the spray bars. In the case of reconstitution of an O/D it is desirable to divide the material, even approximately, into two or three fractions, the finest being narrow, preferably 0/2 to 0/4. In the mixing plants, the carefully screened aggregates are mixed in a dryer and then quickly rescreened before batching. It is possible to improve techniques by improving production procedures, the quality of equipment (batcher, etc.), and methods of sampling and control (statistical) without making particle size specifications more restricting. An overall economic study would doubtless lead to lowering the threshold of efficacy below 87.5 to

  • Supplemental Notes:
    • This report is from the Automotive Engineering Congress Conference held in Detroit, Michigan from 11-15 January 1971.
  • Corporate Authors:

    Laboratoire Central des Ponts et Chausees (LCPC)

    Boulevard Lefebvre 58
    Paris Cedex 15,   France  F-75732
  • Authors:
    • Priede, T
  • Publication Date: 1972-5-6


  • French

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Filing Info

  • Accession Number: 00264855
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Mar 6 1975 12:00AM