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www.trentonpaving.com | Frequently Asked Questions > Aggregate Base: the Foundation

The aggregate beneath the asphalt mat is the structure's foundation.  Just as your house has aggregate beneath its footings, your driveway requires a base of packed stone.  The aggregate serves two purposes.  First, because it does not retain water, it acts as a frost barrier beneath the layer of asphalt avoiding heaving and casting of the asphalt surface in winter.  Second, the packed aggregate base provides a stable layer aiding the asphalt mat support the design load.

Depth of aggregate bases and of asphalt mats will vary depending on (a) the intended use and loads of the driveway and (b) type of sub-soils beneath the drive.

The base of aggregate should be placed in layers not exceeding 6 inches depth to achieve adequate compaction.  If 8 or 10 inches of compacted aggregate are required, the base should be built up in multiple layers.  Adequate compaction of the aggregate is necessary to carry design loads.  This level of compaction is achieved using large 3 Ton vibratory rollers and specially-designed plate packers for residential drives. 

It is often advisable after installing 8 to 10 inches of aggregate to allow an additional 4 to 6 weeks for further settlement of the aggregate base before returning to pave.  After this 'resting' period, the surface is given a final preparation and re-rolled, then paved.

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