Asphalt blowing is a highly temperature-dependent process because the rate of
oxidation increases rapidly with increases in temperature. Asphalt is preheated to 400 to 470(F
(204 to 243(C) before blowing is initiated to ensure that the oxidation process will start at an
acceptable rate. Conversion does take place at lower temperatures, but is much slower. Because
of the exothermic nature of the reaction, the temperature of the asphalt rises as blowing proceeds,
which, in turn, further increases the reaction rate. Asphalt temperature is normally kept at about
500(F (260(C) during blowing by spraying water onto the surface of the asphalt, although
external cooling may also be used to remove the heat of reaction. The allowable upper limit to
the reaction temperature is dictated by safety considerations, with the maximum temperature of
the asphalt usually kept at least 50(F (28(C) below the flash point of the asphalt being blown
(U.S. EPA, 1980).
Asphalt blowing is a highly temperature-dependent process because the rate ofoxidation increases rapidly with increases in temperature. Asphalt is preheated to 400 to 470(F(204 to 243(C) before blowing is initiated to ensure that the oxidation process will start at anacceptable rate. Conversion does take place at lower temperatures, but is much slower. Becauseof the exothermic nature of the reaction, the temperature of the asphalt rises as blowing proceeds,which, in turn, further increases the reaction rate. Asphalt temperature is normally kept at about500(F (260(C) during blowing by spraying water onto the surface of the asphalt, althoughexternal cooling may also be used to remove the heat of reaction. The allowable upper limit tothe reaction temperature is dictated by safety considerations, with the maximum temperature ofthe asphalt usually kept at least 50(F (28(C) below the flash point of the asphalt being blown(U.S. EPA, 1980).
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