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About CoGG8: our material for unsealed roads

Learn how CoGG8 was developed, why we use it on our unsealed roads, and how it performs in different conditions. 

We maintain a large network of unsealed roads across Greater Geelong. Over time, we have trialled different materials to improve how these roads perform in both wet and dry conditions. 

CoGG8 was developed specifically for our unsealed road network. It aims to provide a practical balance between road stability, wet-weather safety, durability and value for money. 

More about CoGG8

An unsealed road needs to maintain its shape so that rainwater can drain from the road surface rather than pool on it. Maintaining this shape helps reduce problems such as potholes and corrugations. 

Historically, some of the materials used on our unsealed roads did not bind together well enough to consistently maintain the required road profile or had too much reactive clay to withstand rainfall. This could contribute to deterioration of the road surface and a greater need for maintenance. 

The City therefore investigated alternative materials that could better hold their shape.

Following two rounds of geotechnical investigations, Gherang gravel was identified as a locally available natural gravel with properties that appeared suitable for our unsealed road network. 

While laboratory results were promising, its performance under real-world conditions highlighted another issue. During wet weather, roads constructed with Gherang gravel could become too slippery. 

The investigation showed that it was not simply the amount of clay in the material that mattered. The way the clay reacted when exposed to water was also important. 

This led the City to work with a local quarry to develop and test a series of different material blends. 

Different blends were trialled with varying material properties and clay content. Through on-road observations and laboratory testing, we looked for a material that could: 

  • hold the required road shape 
  • perform more reliably during wet weather 
  • resist becoming excessively slippery when wet 
  • reduce the development of potholes and corrugations 
  • provide a cost-effective option using locally available materials. 

CoGG8 was the eighth blend developed through this process. 

Testing and field observations found that its properties provided a better balance between retaining the road's shape and performing safely in wet conditions. 

Our gravel road specification requires any gravel used to have the same properties that make up the original CoGG8.

We understand that dust from unsealed roads can be frustrating for nearby residents, particularly during prolonged dry weather. 

All unsealed road surfaces can produce dust. The amount experienced at any particular location can also change depending on weather, traffic and other local conditions. 

CoGG8 was not developed as a dust-free material. Its development focused primarily on achieving an appropriate balance between wet-weather performance, road stability, maintenance requirements and cost. 

The City has also undertaken testing of dust generated from our unsealed road network. Based on this testing, the dust sampled was not identified as presenting a health hazard.  

Dust is an inherent characteristic of unsealed roads. While different materials and conditions can affect the amount of dust generated, an unsealed road is made up of natural materials that weather and therefore cannot provide the same dust performance as a sealed road. 

For this reason, eliminating dust is not one of the service levels provided for unsealed roads. 

Where residents are seeking the higher level of service provided by a sealed road, a road sealing upgrade may need to be considered.

The current mechanism available for residents who want to pursue the sealing of an unsealed road is a Special Rate and Charge (SRC) scheme. 

Under an SRC scheme, benefiting property owners contribute towards the cost of upgrading the road. 

Why does the City continue to use CoGG8?

We recognise that CoGG8 can still generate dust, as will all unsealed road materials. 

However, its performance needs to be considered across the different conditions an unsealed road experiences throughout the year. CoGG8 provides a balance between maintaining the shape of the road, performing in wet weather and providing a cost-effective material for the City’s unsealed road network. 

Based on the materials currently available locally, CoGG8 provides the City with a practical and cost-effective option for maintaining unsealed roads. 

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