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A SUGGESTED MARSHALL METHOD OF DESIGN FOR CUTBACK ASPHALT AGGREGATE PAVING MIXTURE

THIS DESIGN METHOD IS BASED ON THE MARSHALL TESTING PROCEDURE WHICH IS WIDELY USED FOR DENSE-GRADED PAVING MIXTURES OF THE HOT-MIX HOT-LAID BITUMINOUS CONCRETE TYPE. THE RECOMMENDED DESIGN CRITERIA ARE BASICALLY THOSE OF THE ASPHALT INSTITUTE FOR HOT MIXES. THE BINDER CONTENT IS SELECTED AS THAT CORRESPONDING TO 4% AIR VOIDS IN THE COMPACTED MIX. SUFFICIENT QUANTITY OF BINDER FOR PAVEMENT DURABILITY AT THIS PERCENTAGE OF AIR VOIDS IS CONTROLLED BY THE PERCENTAGE OF VOIDS IN THE MINERAL AGGREGATE (V.M.A.). THE LOAD BEARING CAPACITY IS EVALUATED BY THE MARSHALL STABILITY TEST. DETAILED PROCEDURES FOR THE PREPARATION AND TESTING OF THE PAVING MIXTURES ARE THOSE OF THE ASTM WITH A FEW MODIFICATIONS REQUIRED BY THE NECESSARY CURING OF THE CUTBACK ASPHALT. AS IN ASTM METHOD D 1559 THE MIXING TEMPERATURE IS THAT CORRESPONDING TO A BINDER VISCOSITY OF 170 CENTISTOKES. THIS IS DETERMINED FROM THE VISCOSITY-TEMPERATURE CHART OF THE CUTBACK ASPHALT. THE PAVING MIXTURES ARE CURED BEFORE COMPACTION UNTIL SUFFICIENT SOLVENT HAS EVAPORATED TO GIVE TO THE BINDER A VISCOSITY WHICH IS INTERMEDIATE BETWEEN THE MINIMUM REQUIRED FOR SUFFICIENT STABILITY UNDER TRAFFIC AND THE MAXIMUM FOR EASE OF SPREADING AT THE ROAD TEMPERATURE. THIS AMOUNT OF CURING IS SHOWN TO OCCUR WHEN APPROXIMATELY 50% OF THE SOLVENT HAS EVAPORATED FROM MEDIUM CURING (MC) GRADES OF CUTBACK ASPHALTS. HOWEVER, FOR MAINTENANCE MIXTURES WHICH ARE TO BE USED IMMEDIATELY OR ARE TO BE STOCKPILED, THE SUGGESTED AMOUNT OF CURING IS 25%. CURING IN THE LABORATORY IS THUS CARRIED OUT UNTIL THE DESIRED PERCENTAGE OF THE SOLVENT HAS EVAPORATED AS DETERMINED BY DIFFERENCES IN WEIGHT. A COMPOSITION CHART WHICH WILL SHOW THE PERCENTAGE OF SOLVENT VERSUS VISCOSITY AT 140 DEGREES F OF BLENDS OF THE SAME SOLVENT AND ASPHALT BASESTOCK IS THEREFORE REQUIRED TO ESTABLISH THE QUANTITY OF SOLVENT TO BE EVAPORATED AND THE VISCOSITY AT 140 DEGREES F OF THE CURED BINDER. AS IN ASTM METHOD D 1559, THE LABORATORY COMPACTION TEMPERATURE IS THAT CORRESPONDING TO A BINDER VISCOSITY OF 280 CENTISTOKES. IT IS DETERMINED FROM THE VISCOSITY-TEMPERATURE CHART OF THE CURED BINDER. THE CURING TEMPERATURE IS THE COMPACTION TEMPERATURE PLUS 10 TO 20 DEGREES F TO ALLOW FOR HEAT LOSSES DURING THE HANDLING OF THE MIX. THE VARIOUS STEPS IN THE DESIGN PROCEDURE ARE GIVEN IN DETAIL WITH REFERENCE TO THE SPECIFIC TEST METHODS RECOMMENDED. EXAMPLES OF MIX DESIGNS SHOW THAT THE OPTIMUM BINDER CONTENT OF CUTBACK ASPHALT CURED TO A SPECIFIED PERCENTAGE OF ORIGINAL SOLVENT CONTENT IS APPROXIMATELY THE SAME AS THAT OBTAINED WITH ASPHALT CEMENTS. ON THE BASIS OF THE TEST DATA OBTAINED, DESIGN CRITERIA ARE PROPOSED FOR CUTBACK ASPHALT-AGGREGATE PAVING MIXTURES. /CGRA/

  • Supplemental Notes:
    • Vol 11, pp 135-180, 20 FIG, 21 TAB, 7 REF
  • Authors:
    • Lefebvre, J A
  • Publication Date: 1966-11

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  • Accession Number: 00210568
  • Record Type: Publication
  • Source Agency: CANADIAN GOOD ROADS ASSOCIATION
  • Files: TRIS
  • Created Date: Jan 31 1994 12:00AM