Spherical materials are the preferred choice for use in drainage as they leave air spaces for water to flow through. Angular gravels tend to run together over time leaving no such spaces. Materials with lots of fines should also be avoided to prevent pipes from becoming blocked.
A crushed 8-10mm gravel may be inexpensive, but a product such as Lytag® – pulverised fuel ash – could drain up to ten times faster and carries no Government Aggregate Tax. Lytag® is made from the fly ash generated by coal fired power stations which is converted into small round pellets, which are then heated to 1,100°C. This creates a very hard pellet with a honeycombed internal structure of interconnecting spaces. These hard pellets can then be used as a superior, consistent, lightweight aggregate which is up to 50% lighter than natural aggregate.
The advantages of using Lytag® are many, including faster drainage, the ability to retain water in dry conditions which reduces the striping that can occur when gravel is used. It is half the weight of gravel per volume, which reduces the weight of material being carted across the site. It also shatters on contact with mowers, where gravel will not. Lytag® could be the more cost-effective material to use; it will depend on your circumstances.
Summary: (compared to standard aggregate, using Lytag® in land drainage applications):
- Gives up to 10X more hydraulic conductivity (Lytag® = 1.6 x 10-1m/s);
- Releases moisture quicker (15L per m2 @100mm depth)
- Enables stronger root systems (a high void ration improves aeration)
- Has virtually no reduction in volume over time (ideal for bedding pipeline)
- Allows twice as much volume to be carried per truck;
- Is easier to place and
- Offers improved drainage rates and strong plant growth
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