TESTS ON SAMPLES OF BINDERS RECOVERED FROM PREMIX MIXTURES

A PREMIX SURFACING EXPERIMENT WAS LAID ON A ROAD IN DURBAN, IN WHICH A NUMBER OF DIFFERENT TYPES AND GRADES OF BINDER WERE TESTED IN DENSE, CONTINUOUSLY GRADED MIXTURES AND IN ROLLED ASPHALT. THE EXPERIMENT SHOWED THAT CERTAIN MIXTURES HAD CRACKED WHERE AS OTHERS SHOWED NO CRACKING AT ALL OR WERE CRACKED ONLY TO A SLIGHT EXTENT. DEFLECTION MEASUREMENTS SHOWED THAT DEFLECTIONS WERE APPROXIMATELY THE SAME ON THE CRACKED AND UNCRACKED SECTIONS, INDICATING THAT THE DIFFERENCE IN PERFORMANCE COULD NOT BE ATTRIBUTED TO DIFFERENCES IN DEFLECTION. IT, THEREFORE, SEEMS THAT THE CRACKING IS ASSOCIATED WITH THE TYPE OF BINDER USED, AS IT WAS MUCH MORE SEVERE WHERE THE EXPERIMENTAL AIR-RECTIFIED BITUMENS HAD BEEN USED THAN WITH OTHER TYPES OF BITUMEN INCLUDING THE NORMAL MIDDLE EAST BITUMEN. SAMPLES FROM CRACKED AND UNCRACKED MIXTURES WERE TAKEN TWENTY-TWO MONTHS AFTER CONSTRUCTION TO INVESTIGATE WHETHER TESTS ON THE RECOVERED BINDERS MIGHT INDICATE THE CAUSE OF CRACKING, THE BINDER BEING RECOVERED BY MEANS OF THE STANDARD METHOD USING CARBON DISULPHIDE AS SOLVENT. PENETRATION TESTS ON SAMPLES OF THE BINDERS INDICATED THAT WHILE THE BINDERS HAD NOT HARDENED SIGNIFICANTLY DURING THE TIME THEY WERE BEING BROUGHT UP TO THE MIXING TEMPERATURE, CONSIDERABLE HARDENING HAD TAKEN PLACE DURING THE MIXING PROCESS. THE VALUES FOR THE EXPERIMENTAL AIR-RECTIFIED BITUMENS WHICH GAVE RISE TO CONSIDERABLE CRACKING IN SERVICE LIE IN THE AREA BELOW THE CRITICAL CURVE. THIS TENDS TO CONFIRM THE VALUE OF MEASURING BOTH PENETRATION AND DUCTILITY AS MEANS OF DETECTING BINDERS THAT MAY GIVE AN UNSATISFACTORY PERFORMANCE IN SERVICE. THE EXPERIMENTAL AIR-RECTIFIED BITUMENS TESTED WERE AIR-BLOWN TO THE REQUIRED GRADES USING A SOFTER STOCK THAN IS THE PRACTICE WITH THE STANDARD AIR-RECTIFIED BITUMENS NOW BEING PRODUCED COMMERCIALLY, AND WERE CONSEQUENTLY MORE HEAVILY OXIDIZED. IT IS THOUGHT THAT AIR-BLOWING MAY ALSO INFLUENCE THE SETTING-UP CHARACTERISTICS OF THE BINDER SO THAT FATTING UP OF THE ROAD IS NOT SO LIKELY TO OCCUR SOONER AFTER CONSTRUCTION. ALTHOUGH AIR-BLOWING IS ADVANTAGEOUS IN IMPROVING THE RHEOLOGICAL AND SETTING-UP PROPERTIES, IT CAN ALSO HAVE AN ADVERSE EFFECT ON THE BINDER SO THAT CRACKING RESULTS IN SERVICE. SINCE AIR-BLOWING LOWERS THE DUCTILITY IN RELATION TO THE PENETRATION, THE DUCTILITY TEST MAY BE OF VALUE AS A MEANS OF CONTROLLING THE AMOUNT OF AIR-BLOWING THAT IS DONE. THE TWO TYPES OF AIR-RECTIFIED BITUMEN COMMERCIALLY AVAILABLE WERE TESTED IN A PREMIX SURFACING EXPERIMENT. TESTS ON SAMPLES OF THESE BINDERS AND ON SAMPLES RECOVERED FROM THE MIXTURES HAVE INDICATED THAT THEY HAVE A SATISFACTORY DUCTILITY.

  • Supplemental Notes:
    • Annual Rept 1965, SPECIAL REPT PAD 14, PP 6-7
  • Corporate Authors:

    Cncl Scient & Indus Res /S Africa

    /Nat Inst Road Res
    ,   USA 
  • Publication Date: 1966

Subject/Index Terms

Filing Info

  • Accession Number: 00210729
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 1 1970 12:00AM