The Lime Association of Texas recently had an opportunity to travel to Yellowstone National Park. Catastrophic flooding in 2022 left the park dealing with many washed-out roads. Park administrators and staff have replaced or repaired much of the damaged pavement from that event and are now turning their focus back to the routine maintenance of approximately 250 main lane miles of asphalt roadways and nearly 150 miles of secondary/side roads.
Road reconstruction, repairs, and maintenance all play a vital role in keeping the roadways in excellent shape for the traveling public. Lime has been successfully used throughout the road construction process for decades and continues to be a vital tool in extending the life of most any pavement structure. Lime has traditionally been used in both subgrades and asphalt wearing surfaces to enhance long-term pavement performance.
In Yellowstone National Park, while the subgrade does not typically require lime treatment, the asphalt surfaces are routinely enhanced by using 1% hydrated lime not only as an antistrip but also to extend the life of the asphalt. With regard to oxidation, studies have shown that adding lime to the asphalt mix can extend the life of the road by as much as 30-35%. For Yellowstone, the benefits of using lime are even more imperative, due to the extreme exposure to climate and moisture for months at a time.
After driving most of the roads in the park, it is apparent the park staff responsible for repairing and maintaining the roadway infrastructure have done an outstanding job of making sure the roads are safe for approximately three million people who visit the park each year.
During our visit, we were able to observe a milling and pavement operation that was in progress in late August 2023. The pavement rehabilitation consisted of milling approximately 2.5 inches of the existing damaged surface and replacing it with a new wearing surface that is expected to last some twenty-plus years. The new surface is a Superpave 1/2 inch nominal aggregate size mixture with a PG 58-34 asphalt binder. This surface will receive a seal coat approximately one year later which will help preserve that asphalt wearing surface for years to come. We also had the opportunity to visit the on-site asphalt production facility where the asphalt mix is produced. Beyond the standard equipment that makes up a portable asphalt plant, the plant included a silo for lime and a lime feeder system that allows lime to be added to the asphalt mix during production.
By adding 1% of lime to the asphalt mix, the asphalt is enhanced as follows:
- Improves the adhesion between the asphalt binders and aggregates
- Improves the resistance of the mixture to fracture growth, especially at low temperatures
- Behaves as an “active” mineral filler by stiffening the asphalt binder without making it brittle
- Favorably alters the oxidation kinetics of the mastic by reducing the damaging effects resulting in lower viscosities over time
- It alters the plastic properties of clay fines contaminating the aggregates, reducing moisture and rutting damage over the life of the pavement
When tasked with the responsibility for long-term pavement performance and durability, you should always consider lime, one of the most VERSATILE CHEMICALS.