Asphalt, or bitumen as it is sometimes called, is widely used throughout the construction industry. In an effort to make an already useful product more useful, over 100 years ago chemists developed a stronger and more stable version called blown asphalt or oxidized bitumen with the addition of air.
How is it made? What are the differences between blown and regular asphalt and what makes it more desirable? Let’s find out.
Making Blown Asphalt
Blown asphalt begins its life much like any other asphalt. It is taken from the bottom of a vacuum distillation unit in a refinery, however blown asphalt is then taken through an additional oxidation processing step.
The temperature of the vacuum tower bottoms is maintained in the blowstill between 450°F and 500°F while air is blown into it. While this process is often called oxidation (resulting in oxidized bitumen) there are more reactions going on during the air blowing process. Some of these reactions include dehydrogenation, condensation, polymerization and many others.
Once the desired characteristics for that batch are met, the process ends and the asphalt is then sent to storage for shipment by truck or rail. It may also be used on site for the production of roofing products. Typical end point parameters include a softening point 215°F and a penetration of 20 for roofing grade asphalts. Common grades of paving grade asphalts are 95-25, 85-25, 90-40 and 115-15. Some paving grade asphalts are modified by adding polyphosphoric acid to blowstill prior to starting the air flow.
Properties of Blown Asphalt
There are several advantages to blown asphalt. One is that it is much more chemically stable than regular asphalt. This stability also translates into added durability.
One of the more interesting features that blown asphalt has is a higher softening point. This means that it can remain in place longer than alternatives. It retains the additional durability during the elevated temperatures, as well.
Blown asphalt is completely water resistant, making it well suited to a variety of sealant and joint filling compounds. It is also more flexible than regular asphalt, which is why it is often used to make roofing products such shingles.
Uses of Blown Asphalt
Blown asphalt has a wider range of uses due to its water resistance, added durability and chemical stability. Approximately 90% of the asphalt produced in the US goes into paving and 10% goes into roofing products such as shingles and rolled roofing products.
There are many other special applications that include:
- Pipe coating enamels
- Concrete joints
- Waterproof lining for reservoirs and canals
- Sound dampening felts
- Anti-slip coatings
Converting your Asphalt Operation or Upgrading with COSTELLO’s Bubble BreakerSM technology
Would you like to add the capability to produce blown asphalt on site. Would you like to reduce operating costs at your existing blowstill? Then you might want to consider adding the ability to produce blown asphalt at your current facility or modernizing your existing operation with COSTELLO’s Bubble BreakerSM technology.
With the COSTELLO, technology the oxidation process is enhanced by the utilization of small air bubbles rather than big bubbles. For example: 512 – ¼” bubbles have the exact volume as one 2” bubble, however, the small 512 – ¼” bubbles have 8 times the surface area of a single 2” bubble.
COSTELLO’s Bubble BreakerSM technology has seven (7) benefits:
- The oxidation chemical reaction only occurs where the surface of the air bubble touches the asphalt. This means that less air (a lower flow rate) can be used to achieve the same end point.
- This also infers that less air will flow to your air pollution control device thus reducing the size of your thermal oxidizer and natural gas usage.
- The lower the gas velocity at the top of the blowstill also insures less aerosol droplets get to the knockout pot and ultimately the thermal oxidizer. This can increase the product mass by up to 1.5%. Burning aerosol droplets may seem like free fuel but compared to burning natural gas in your thermal oxidizer it is very expensive. If asphalt has 18,200 BTUs per lb. and asphalt cost $0.25 per lb. then asphalt as a fuel cost $13.74 per mmBTUs.
- The COSTELLO technology will reduce the typical batch cycle time by half.
- In addition there is improved heat transfer.
- There is longer blowstill life since there is no cooling water dumped on the outside thus creating thermal stresses and metal fatigue.
- No internal water cooling that requires an oversized thermal oxidizer to handle the water vapor created.
COSTELLO has a full team of experts on hand that can help you modify your facility to include the latest technology in blowstill design.
Contact COSTELLO today to discuss the benefits at your facility.