It’s estimated that the United States has over 4 million miles of road, including about 49,000 miles of interstate highways and 620,000 bridges, all culminating in a vast and complex infrastructure system that handles over 8 billion vehicle miles per day. All that driving takes a toll on the pavement used on the 2.3 million miles of paved roads, which demand periodic maintenance or pavement preservation to ensure they stay safe and comfortable for drivers and pedestrians.
The need for pavement preservation is growing. As extreme weather events become more common and the price of oil and asphalt rise, transportation authorities need more effective solutions to keep roads intact while reducing maintenance.
Polymer modified asphalt emulsions can help. Polymer dispersions for asphalt modification from BASF are designed to enhance the mechanical properties of pavements, resulting in greater durability, increased driving comfort, reduced road maintenance costs, and a reduced impact on the environment.
Pavements, pricing, and preservation
As a partial by-product of the crude oil refinery process, the price of asphalt is directly correlated to oil prices. Over the last 10 years, asphalt rose an average of 0.7% for every 1% increase in the price of crude oil.
Rising oil prices can impact transportation and asphalt installation expenses for paving projects, further adding to the cost.
“Sometimes there's a shift in asphalt prices that goes beyond the price of oil because some refineries don't make asphalt. Instead, they will use the bottoms of the refinery for petroleum coke or other products rather than make asphalt,” says Arlis Kadrmas, Senior Technical Specialist at BASF. “Agencies know that pavement preservation works, so BASF’s role is to help our customers apply the right product on the right pavement at the right time.”
Rising prices is only one reason to keep pavement in good shape. Effective pavement preservation means fewer repairs down the road, ultimately saving on maintenance costs in the long run. More importantly, it also promotes a safer and more comfortable driving experience for everyone.
By incorporating a proactive approach, the damage from freeze-thaw cycles, water, heavy traffic and solar rays can be mitigated before more extensive work or repairs are needed.
Pavement preservation procedures
From filling small cracks and voids to completing thin lift overlays, BASF offers polymer solutions for all types of asphalt maintenance. Two of the most common preservation techniques are chip seals and micro-surfacing.
“Chip seals used to be widely seen as a method used on low volume roads, but the quality of chip seals has improved enough over time to be used on higher volume roads,” says Kadrmas. “Chip seals not only help to seal the road and keep the environment away from the pavement underneath, but they also provide a safe and skid-resistant driving surface for the public because of the aggregates used on the road.”
In a similar vein, micro-surfacing is a treatment that combines polymer-modified emulsified asphalt, mineral aggregate, mineral filler, water and other additives that are mixed and spread with a machine over the road surface.
“Micro-surfacing also helps to seal the road from the environment,” says Kadrmas. “Its application looks very similar to a hot mix, and it can be used to fill in any ruts that might be in the pavement from wheel paths. It also helps to level and improve the smoothness of the road, and the aggregate provides skid resistance.”
Another benefit of micro-surfacing comes in the form of how it “breaks” or hardens: while chip sealing relies partially on the evaporation of the water in the asphalt emulsion, the asphalt emulsion used in micro-surfacing contains additives that allow it to break without relying on the sun or heat for evaporation to occur.
This means road work can be done overnight, reducing unnecessary traffic hold-ups and offering a cooler work environment for road work crews in hotter states.
The right emulsions
The choice of polymers used in a modified asphalt varies based on application type.
“BUTONAL® NX 4190 is used mainly in micro-surfacing, but with some asphalt, customers may use BUTONAL NS 198 to get results that meet agency specifications,” says Kadrmas. “BUTONAL NX 4190 is used in cationic chip seal systems, while BUTANOL NX 1129 is used in anionic chip seal systems.”
BUTONAL NX 1129 is a mechanically stable latex polymer dispersion that is readily incorporated into anionic asphalt emulsions through addition to the soap solution or co-milling, while BUTONAL NX 4190 is a mechanically stable latex polymer dispersion that is readily incorporated into cationic asphalt emulsions through addition to the soap solution or co-milling.
The choice of whether to use a cationic or anionic system depends on a variety of factors, including the geological composition of the asphalt blend, state aggregates, and other factors.
Regardless of where it takes place or which application pavement preservation uses, the benefits are clear. Pavement preservation is an important and effective way to keep road infrastructure safer, more durable and more comfortable for longer periods of time. Studies have shown that there are sustainability benefits to the practice as well.
“BASF has conducted some eco-efficiency studies on these asphalt emulsion pavement preservation techniques and compared them what's called ‘mill and fill’ procedures,” says Kadrmas. “These studies have shown that these pavement preservation techniques are very eco-efficient, both in terms of the products themselves as well as the reduced volume of materials that they use,” says Kadrmas. “The polymers may cost a little more, but they pay for themselves in the extra lifetime that they provide the roads.”
Learn More about BASF’s modified asphalt solutions