The Evolution of Asphalt Heating

The ancient Romans were the first great engineers and roadbuilders over two millennia ago, and parts of the roads they built can still be seen today. After the Romans, the prepared surfaces of engineered roads were built using clay, mud, stone, brick, and even wood block.

However, for over 100 years, the most common, durable road surface has been the black cement-and-aggregate mixture called hot-mix asphalt. It is also known as as macadam or bitumen in other English-speaking regions of the world.

asphalt heating

Ancient Roman road of Tall Aqibrin

Asphalt Heating

Asphalt was initially mined from pitch lakes in the Trinidad islands and similar deposits around the world. It was originally mixed manually with gravel in big metallic trays heated over fire.

Natural asphalt, used in this difficult process, was later replaced by an engineered formula derived from crude petroleum, and the heating process and mixing technology quickly evolved. Rotating drums used to mix cement were initially adapted for mixing purposes.

Asphalt Lake, Trinidad. 19th Cent.

Asphalt Lake, Trinidad. 19th Cent.

In the 1920s or 1930s, some asphalt producers who were supplying material for roadbuilding as well as for roofing and pipe-dipping, began to employ an indirect heating method to improve the consistency and uniformity of the end-product, as direct heating was difficult to control.

As mentioned in a 1931 issue of The Journal of Industrial and Engineering Chemistry, diphenyl vapor, steam, and hot oil were among the media used in indirect heating of asphalt tanks.

The evolution continues to this day. The hot oil used in the 1930s to heat asphalt tanks was a lubricating-oil base stock, not designed for heating, but to protect metallic surfaces, and extend the life and improve the operation of rotating machinery.

Modern heat-transfer fluids are designed specifically for high-temperature service environments. These fluids are derived from various chemical families to ensure long life, rugged service, and to prevent deterioration caused by heat and oxidation.

Hillside Roadcut, Asphalt Paved

Hillside Roadcut, Asphalt Paved

Similarly, heating equipment has also evolved a long way from the simple heated trays that were manually stirred using long metallic hoes. The 1960s saw producers moving beyond hot-oil heated asphalt plants and adding storage tanks and surge bins for more flexibility to cater to varying demands.

Other methods were developed to extend the workability time and distance range of the product leaving the plant hot and ready for roadbuilding. Information systems and advanced computer systems used for supply, testing, heating, logistics, and environment control have added a whole new level of sophistication for asphalt plant operations.

Heating Asphalt, 1930s (Img. from

Heating Asphalt, 1930s (Img. from

Paratherm’s Heat Transfer Fluids

Paratherm works with asphalt construction equipment OEMs to help both companies customers systems maintained and running, especially when needed the most.

In North America, the paving season peaked in the month of August 2016.

One of the equipment specialist companies in the field of asphalt-paving is Meeker Equipment Company Inc., which manufactures components for upgrading, renovating, and retrofitting existing ready-mix and asphalt plants.

[On the 2016 paving season] We hear from our customers that generally speaking the paving season is going very well. Certain areas see a bit of trouble, usually related to political issues. New Jersey in particular needs attention to their transportation trust fund, so there’s a slowdown there at peak season. We also see a lot of paving companies reinvesting in their asphalt plants. Money that had been sitting on the sidelines is now going back into rebuilding their businesses.

Jeff Meeker, President of Meeker Equipment

Meeker also expressed his opinion on the evolving role of indirect heating and how heat transfer fluids are important elements for preventive maintenance practices during the production process.

Well, our people have become more plugged into talking to construction companies about their hot oil in these equipment discussions, and how important it can be for their operations. These days, when we visit our customers, our people always carry a heat-transfer-oil test kit. The plant managers and maintenance men are increasingly realizing the value of their hot-oil equipment, its impact and importance for their asphalt plants. So we can give them a test kit right there and get them started to evaluate the condition of the system based on the oil test results.

Jeff Meeker, President of Meeker Equipment

This information has been sourced, reviewed and adapted from materials provided by Paratherm.

For more information on this source, please visit Paratherm.


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