Asphalt pavement consists primarily of two key ingredients: crushed stone aggregate and asphalt binder, often sometimes referred to as bitumen. While asphalt produced with just these ingredients can last for many years, as time goes on, the asphalt binder falls prey to the forces of age. This deterioration causes the pavement to grow brittle and weak, often leading to damage.
In order to create stronger, longer-lasting asphalt, paving contractors often add modifiers to their asphalt binder. One of the most thrilling yet less-used types of asphalt modifiers goes by the name of lignin. Take a closer look at three exciting benefits tied to the use of lignin as a modifier in asphalt binder.
1. Better Resistance to Oxidation
The principal threat facing all asphalt pavement comes with oxidation. Oxidation happens naturally as the result of exposure to oxygen, sunlight, moisture, and other natural elements. Oxidation causes the asphalt binder to grow progressively more brittle. This loss of elasticity puts the asphalt at a much greater risk of developing cracks, potholes, and other forms of structural failure.
Contractors incorporate lignin into the asphalt binder during the manufacturing phase, with the goal of increasing the asphalt’s long-term resistance to oxidation. Lignin is a type of complex polymer naturally derived from plant matter. It has strong antioxidant properties and has been shown to reduce the rate of aging in asphalt pavement.
Scientists tested this by subjecting different blends of asphalt to oxidizing agents and then analyzing the chemical composition of the asphalt binder. Those binders that contained lignin showed a reduction in chemical compounds associated with oxidative degradation. In other words, lignin succeeds at improving the long-term stability of asphalt pavement.
2. Improved High-Temperature Properties
Lignin comes in the form of very tiny fibers. The rough surface of these fibers allows them to easily adhere to asphalt, thus increasing the asphalt’s internal strength. As a result, asphalts modified with lignin tend to be stiffer than regular asphalt, yet without the sacrifice in bond strength normally associated with oxidation-related stiffening.
The enhanced stiffness of lignin-modified asphalt improves its resistance to such common forms of damage as rutting and shoving. These types of damage happen when asphalt deforms under the heavy weight of vehicles. Increasing the stiffness of the asphalt has a particular benefit for asphalt pavement in hot parts of the country.
Extreme summertime temperatures in such regions often cause asphalt to become excessively soft, making it much more susceptible to rutting. The increased stiffness associated with lignin modification allows asphalt to maintain more structural integrity at high temperatures.
3. Low Cost
Lignin ranks as the second most common biological polymer, with only cellulose being more common. Ethanol production, paper-making, and many other manufacturing processes generate large amounts of lignin as an unwanted by-product. In fact, every year global industries produce over 50 million tons of waste lignin.
This abundance of largely unwanted lignin means that it can be obtained for incredibly low prices. As a result, asphalt manufacturers can offer improved paving materials at a minimum cost to consumers. By comparison, synthetic asphalt modifiers often require much more intensive manufacturing processes, which, in turn, increase their cost to consumers.
Not only does lignin exist in abundance, but it constitutes a relatively environmentally friendly material. For one thing, incorporating lignin reduces the overall amounts of non-renewable asphalt used. The non-toxic nature of lignin also means that it poses little risk to manufacturers and pavement installers.
Lignin offers a number of exciting benefits when used as a modifier in paving asphalt. For more information about whether lignin-modified asphalt would make a good choice for your next paving project, please contact the paving experts at JR Paving & Construction Co., Inc.