For low-volume roads, chipseal can provide a cost-effective wearing surface compared with traditional hot asphalt paving. However, it can come with potential issues. Shelling, delamination, potholes, and spiderweb cracking are all common problems faced with chipseal roads that need addressing before they become bigger problems. Many county officials blame the asphalt emulsion or aggregate chip quality, but an NCHRP report suggests that because chipseal is a non-structural preservation treatment for the surface only, early cracking and failure can occur due to flexing and other subbase issues.
In fact, the chipseal may not be the problem at all. According to a report prepared for the Transportation Research Board, unsealed subbases absorb water and lose density quickly, which indicates that creating a stabilized, well-compacted subbase is essential for best results on your roadway.
Compacted aggregate is often used as the subbase for roads that use a chipseal finish. Even when fully compacted, however, aggregate is prone to shifting and can react poorly to severe climate conditions depending on the type of aggregate used. There are three common ways that these subbases can fail.
While chipseal holds up well under normal traffic conditions, heavy axle loads can put significant stress on the surface layer. If the subbase beneath the surface is not strong enough, this stress can cause flexing which eventually leads to cracks in the bottom of the surface layer. Some crews attempt to fix this flexing by adding a new layer of chipseal, but when those heavy axles come back through or weather causes subbase expansion, those underlayer cracks can transfer stress and cause mirrored cracks in the new surface. This is known as reflective cracking.
Another potential problem for chipseal roads is when water creeps into the subbase through cracks and edges. The water causes the aggregate to become less compacted and more vulnerable to shifting when heavy vehicles pass over the chipseal surface. As the aggregate shifts, the water mixes with clay and silt particles, and that gets forced up into the cracks in the surface. All this shifting in the subbase creates more instability in cracked areas especially when the trapped water freezes, causing voids and ultimately leading to potholes forming. Those potholes can make your road dangerous for vehicles if not fixed quickly.
Cold winter conditions are especially harmful to chipseal roads. Any water trapped in the aggregate subbase freezes when the temperature dips too low. That frozen liquid expands, which causes upward pressure toward the surface. Because chipseal is a thinner layer, this upward pressure can cause ridges and bumps, which ultimately allow more liquid to enter and freeze. Then spring comes.
With the warmer temperatures, the road begins to thaw from the top down. With the lower layer still frozen, the upper layer of thawing liquid and mud can only shift when pressure is applied to the surface. Because chipseal is thinner than traditional asphalt applications, it can’t distribute the weight, and normal traffic then causes potholes, cracks, and ruts.
As an alternative to an aggregate subbase, Perma-Zyme is an enzyme stabilizer that works with your native soil to create a concrete-like subbase for your road. While it can also be used as a stabilized unpaved road, covering the Perma-Zyme stabilized subbase with a chipseal topcoat can make your road last longer and create a smoother ride.
The process is very simple: the positive enzymes within Perma-Zyme are attracted to the negative charges within the soil, which creates a bond when compacted. After being properly compacted, the stabilized soil takes 72 hours to cure. After the curing period, the treated soil continues to gain strength over time, and the end result is a strong subbase that can withstand severe weather, freeze-thaw conditions, and even heavy traffic.
This stabilized road base can better handle wet conditions because the bond keeps the water from creating space and shifting the way it does in aggregate subbases. And by strengthening the soil by up to 10x, it can withstand mixed traffic conditions, including heavy axles and industrial equipment. This stronger subbase ensures the chipseal has less upward pressure to keep the road in better shape.
See how Grayson County was able to fully rehabilitate a chipseal road that had significant wear and tear in less than a week by treating the soil with Perma-Zyme before resealing.
A cement subbase offers the highest compressive strength of the stabilization options. However, the high strength makes cement subbases extremely brittle. This can lead to reflective cracking in chipseal topcoats because it doesn’t distribute weight evenly the way that asphalt does. Cement stabilization works best with gravel and silt soils.
Lime is another stabilization option that can create a strong subbase. It can work under chipseal, but it requires very specific soil types to work properly, such as highly-plastic, clay-heavy soils. It also needs exact measurements for the best results, and application can be hazardous without the right safety precautions.
Perma-Zyme cures faster than lime and cement and generally offers the most flexible solution. Because it is not brittle like cement, it risks less reflective cracking. And because it is non-hazardous and non-corrosive, it does not require specialized chemical-handling equipment, although crews should still follow normal job site safety practices and SDS guidance. Perma-Zyme works best with soils that contain sufficient reactive material, such as clay, limestone, or decomposed granite, along with coarse material for strength. Some soils may require amendments depending on their existing composition.
If you start with a strong foundation, a chipseal-coated road will last longer and be less likely to experience common failures. Choosing the right stabilization method for your subbase is the best way to create that strong foundation before adding the chipseal topcoat. Perma-Zyme can help you create a stabilized road base for your roads that can last for years.