Understanding Road Distresses: Raveling

Unless you are an engineer or road manager, it can be difficult to distinguish between different road distresses. To help you understand different types of road distresses, let’s talk about raveling.

Raveling is the disintegration of an asphalt road surface due to the dislodgment of the aggregate materials (gravel, sand, and crushed stone). It reduces skid resistance, roughens the road surface, and exposes the layers underneath to further deterioration. Raveling also results in loose gravel that can damage vehicles or create dangerous driving situations.

Remember Pop Rocks? Driving over a raveled road will sound similar to the candy crackling on your tongue.

Why Raveling Occurs

Raveling can occur due to the following reasons:

• Age: Asphalt pavements ravel when the asphalt binder ages and hardens.
• Traffic: It occurs commonly in high traffic areas due to wear and tear. If there is a lot of truck traffic (heavier loads), the chances of raveling are even higher.
• Poor Aggregate Mix: The asphalt mix should have a proper balance of different sized rocks, to ensure that it packs well, without forming air gaps. Fine particles, like sand, are a crucial component because it produces a solid packing structure. The mix ratios should be calculated based on the local climate and expected traffic loads.
• Poor Compaction: Good pavements have high density, which requires adequate compaction. Without proper compaction, the aggregate will not bond well with the binder. Asphalt should be compacted at higher temperatures (a minimum of 290℉ or higher) to ensure proper binding.
• Dust: Accumulation of dust causes the binder to adhere to the dust, which will ultimately weaken the aggregate bonding. Deterioration accelerates with vehicular traffic.
• Moisture: The presence of moisture during paving makes the binder ineffective at adhering to the aggregate.

How to Fix Raveling

First, the pavement must be assessed. Second, the pavement repair must be planned based on the severity of damage that has occurred: 

• For low severity raveling (localized), you’ll need to remove the raveled area and then patch it.  
• For high severity raveling (widespread), you’ll want to remove the damaged area and apply an overlay.  

Prevention is Essential

What matters most is prevention.

When constructing new roads, choose a high-quality binder and a balanced mix of aggregates recommended for local weather conditions. Different climates and regions require specially formulated aggregates and binder content to allow pavements to function optimally and last longer without wearing down. 

Use a preventative sealant layer based on traffic volumes. This could be a fog seal, a seal coat, micro-surfacing, or a thin overlay of hot-mix asphalt (HMA Thin Overlay).

And finally, the simplest and most cost-effective way to prevent raveling is to keep the streets clean.