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  • Writer's pictureG&G Services

Why Class 6 Road Base Outperforms Washed Rock for Road Construction

Class 6 road base is often considered a better option than washed rock for several reasons, particularly in the context of creating a stable and durable foundation for road construction and paving projects. Here are the key reasons why:

1. Compaction and Stability

  • Compaction: Class 6 road base contains a mix of fines, sand, and larger aggregates that allow it to compact more effectively than washed rock. The fines fill the voids between the larger particles, creating a dense and solid mass when compacted. Washed rock, being free of fines, does not compact as well, resulting in a less stable base.

  • Stability: The ability to compact tightly gives Class 6 road base greater stability and load-bearing capacity. Washed rock, lacking fines, tends to shift and settle more over time, which can lead to a less stable surface.

2. Load Distribution

  • Load Bearing: The mixture of particle sizes in Class 6 road base helps to distribute loads more evenly across the base layer. This uniform distribution minimizes the risk of deformation and rutting under heavy traffic. Washed rock, on the other hand, primarily consists of larger particles that do not distribute loads as evenly, leading to potential surface instability.

3. Drainage and Erosion Control

  • Controlled Drainage: While both materials allow for some drainage, the fines in Class 6 road base help to control the rate of water flow through the base. This controlled drainage is crucial in preventing erosion and maintaining the integrity of the base layer. Washed rock, with its higher permeability, can allow water to flow too freely, potentially undermining the base structure over time.

  • Erosion Resistance: The compacted nature of Class 6 road base makes it more resistant to erosion. Washed rock, lacking fines and compactability, can be more susceptible to erosion, especially in areas with significant water flow.

4. Cost-Effectiveness

  • Material Cost: Class 6 road base is generally more cost-effective than washed rock. The production process of washed rock, which involves additional washing to remove fines and impurities, can be more expensive.

  • Installation and Maintenance: The better compaction and stability of Class 6 road base can lead to lower installation and maintenance costs. It provides a longer-lasting foundation, reducing the frequency and extent of repairs needed over time. Washed rock may require more frequent maintenance due to shifting and settling.

5. Versatility

  • Wide Range of Applications: Class 6 road base is suitable for a broader range of applications, including roadways, driveways, and various types of pavement support. Its balanced mix of materials makes it versatile for different construction needs. Washed rock, while useful in some contexts, is more limited in its applications due to its lack of fines and compaction ability.


While washed rock has its uses, particularly in drainage applications and decorative landscaping, Class 6 road base is typically the preferred choice for creating a stable, durable, and cost-effective foundation in road construction and paving projects. Its superior compaction, load distribution, erosion resistance, and overall stability make it a more reliable and efficient option.


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