What is Blown Asphalt ?
Air-blowing: The manufacturing process used to make oxidized roofing asphalts in which air is blown through an asphalt flux. An exothermic oxidation reaction occurs, yielding asphalt that is harder, more viscous, less volatile, and less temperature-susceptible than the asphalt flux used as the feed stock to the process.
Asphalt, oxidized (blown or air-refined): Asphalt treated by blowing air through it at elevated temperatures to produce physical properties required for the industrial use of the final product.

Blown Asphalt Explain: 
Special properties may be imported to asphalt by blowing air through the topped crude fraction during the latter part of the refining process. The regular distillation process is discontinued at some point while the topped crude is still liquid. The heavy fraction is then put into a converter and air is blown through it while it is maintained at a high temperature. This process is continued until the asphalt has attained desired properties. Often, such asphalts are called oxidized asphalts. However, this is not strictly a true term because not only oxidation but also vaporization, Dehydrogenation, condensation, polymerization and other reactions occur during the air blowing process.

Blown Asphalt Uses:
Blown Asphalts are used for a wide variety of industrial and specialty purposes. Just a few of these are: a variety of roofing applications, pipe coating enamels, underselling asphalts to sill cavities beneath Portland cement concrete pavements, and waterproof membranes for lining canals and reservoirs. In many instances blown asphalts are applied in pure form. In other cases, very fine mineral powders (fillers) are mixed with blown asphalt prior to application. Only rarely, if ever, are blown asphalts used in asphalt-aggregate mixtures for paving purposes.