The American Chemistry Society (ACS) has designated this week (Oct. 16-22) to be National Chemistry Week. All across the United State, “local ACS sections, businesses, schools, and individuals are invited to organize or participate in events in their communities with a common goal: to promote the value of chemistry in everyday life.” Bituminous Roadways, Inc. is contributing to this common goal by providing some simplified insight into the chemistry of asphalt.


Picture of an asphalt core, showing rocks and sand

Asphalt pavement core showing the rocks and sand that make up a large percentage of the asphalt pavement.


Did you know that asphalt pavements are 95% rocks and sand?
The asphalt binder is the black glue that holds asphalt pavements together, and it makes up only 5-7% of asphalt pavements. The rocks and sand provide some strength to the pavement, but the small percentage of asphalt binder has a huge impact on the overall strength and performance of asphalt pavements.

Did you know that asphalt pavements are flexible?
Although it can be very hard to see, asphalt pavements are designed to bend and flex underneath the load of car or truck tires. Asphalt binder is a viscoelastic material, meaning that it has the characteristics of a liquid and a solid at the same time. At room temperature, asphalt is pretty stiff, but if you left it sitting on your desk, it would very slowly flow outwards like a spilled liquid. Asphalt binder is also a temperature dependent material, meaning that as temperatures increase the asphalt becomes more flexible and more like a liquid, and as the temperatures decrease the asphalt becomes solid and brittle like glass. The very best asphalt binders are modified specifically for the weather conditions of a certain region. The modifications are designed to keep the asphalt pavement flexible at regional low temperatures and stiff enough at regional high temperatures. Here at Bituminous Roadways, we personally modify asphalt binders for the Minneapolis-St. Paul Metro region.

diagram of a refinery process

This simplified drawing shows many of a refinery’s most important processes.


Did you know that asphalt binders are a product from refining crude oil?
Much like gasoline and other petroleum based fuels, asphalt is produced by refining crude oil. Crude oil is heated to very

high temperatures causing the lighter oils and fuels to turn into gases. As these gases rise to the top of the distillation tower, they cool down and turn back into a liquid at different levels. In the very bottom of the distillation tower is everything that did not turn into a gas, this leftover material is the asphalt binder. Bituminous Roadways stores asphalt binder at its three asphalt plants in Minneapolis, Inver Grove Heights, and Shakopee, MN.


Do you know much about the chemistry of asphalt binder?
If you do, you should be very proud of yourself. Asphalt chemistry is a very complex subject and not well understood even by experts in the field. In the very simplest terms there are two types of molecules that make up asphalt: 1) Asphaltenes and 2) Maltenes.

Asphaltenes are solid complex components that like to combine together. Asphaltenes provide the strength and stiffness to the asphalt.  Maltenes are resins and oils that disperse the asphaltenes. Maltenes keep the asphalt flexible.

image of a asphaltene molecule


drawing of a maltene molecule



Did you know that asphalt ages?
The aging of asphalt is called oxidation. Oxidation is caused by time, temperature, and exposure to oxygen. Asphalt pavements oxidize slowly over time, and typically take 10-15 years before they are fully oxidized. When asphalt binder is oxidized the Maltenes turn into Asphaltenes. This makes the asphalt stiffer, less flexible, and more susceptible to cracking. Bituminous Roadways is the sole Minnesota supplier of an asphalt rejuvenating seal coat called BIORESTOR™ (see BIORESTOR™ Blog Post). BIORESTOR™ is a soy oil based rejuvenator that replenishes some of the maltenes lost due to oxidation. This makes the pavement more flexible, seals the pavement against water permeability, and can prolong the life of your pavement.

drawing of molecules well dispersed

Flexible Asphalt – Asphaltenes are well dispersed

drawing of molecules grouping together for stiff asphalt

Stiff Asphalt – Asphaltenes are grouping together


Here at Bituminous Roadways, we strive to provide our Minneapolis-St. Paul customers with the highest quality asphalt pavements possible. We work towards this goal by being knowledgeable about every aspect of asphalt pavements, including the complex subject on asphalt chemistry. For more information about Bituminous Roadways, asphalt maintenance, asphalt paving, asphalt materials, or to get an estimate, please contact Bituminous Roadways at (651) 686-7001 or visit our website.