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THE TRIALS AND TRIBULATIONS OF SURFACE DRESSING ---PAPERS PRESENTED AT THE IHT CONFERENCE, 1986, LONDON

The problems associated with surface treatment are identified and ideas for future development of materials and plant are suggested. The properties of an ideal surface dressing binder are summarised and the conflicts which exist between several of these ideals are identified. Fluxed binders (cut back bitumen and tar bitumen blend) are compared to these ideals. Their limitations include: (1) too high a fluidity when road temperatures are above 30 degrees c; (2) poor adhesion to damp aggregate below 18 degrees c, and none below 12 degrees c; (3) binder without adhesion agents is easily stripped from stone in the presence of water even after initial adhesion; (4) in order to spray through atomizing jets, temperatures of 140 -165 degrees c are required, which is well above the flash points of the kerosene or creosote used; (5) the residual binder has variable properties depending on flux evolution and is too temperature susceptible. Emulsions have the following limitations: (1) the rate of break is too long; (2) the residual binder is still too temperature susceptible and will flow at high road temperatures and is brittle at low temperatures; and (3) the viscosity of the emulsion after spraying is low leading to flow on the road from high points, which can cause problems if not chipped up quickly. In summary, emulsions adhere better in damp conditions whereas hot flux binders have superior initial cure. Emulsions have practical advantages, as well as the safety advantage of being a low temperature binder. The limitations of the conventional binders are only important when considering the more difficult sites where the initial ability to hold chippings against traffic forces is important, especially at road temperatures above 25 degrees c. The future design of binders is discussed, in particular, the addition of polymers. Those offering the greatest potential are the styrene butadiene styrene, or rubbers, ethylene vinyl acetates and acrylics. The properties of an ideal chipping are: excellent adhesion to bitumen, high polished stone value (psv), high strength, good shape, dust free, and light coloured to reduce road pavement temperatures and to increase reflectivity for night driving. Future developments to improve adhesion include chemicals to precoat the stone to make it hydrophobic, and lightly coated chippings made from emulsions. High psv, price, adhesion, shape, colour and hardness need to be considered in the selection of chippings. The use of artificial aggregates is foreseen especially on difficult sites. Contracting problems are also considered and include broken windscreens, quartering and productivity. A tightening of specifications can reduce risk-taking undertaken because of inclement weather. Developments affecting sprayers, chipping spreaders, rollers and sweepers are outlined, together with the qualtiy control and testing of the spray bar.

  • Corporate Authors:

    INSTITUTION OF HIGHWAYS & TRANSPORTATION

    6 ENDSLEIGH STREET
    LONDON,   United Kingdom  WC1H 0DZ
  • Authors:
    • HESLOP, M W
    • Broadbridge, M H
  • Publication Date: 0

Language

  • English

Media Info

  • Pagination: 16 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00487867
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Sep 30 1989 12:00AM