The success of any construction project begins with the foundation, and building a new driveway is no exception. If the foundation – the sub-base below the asphalt – is not built correctly you’re bound to have problems in the future. This sub-base is the true foundation for your driveway has two primary jobs:
- It provides a stable surface to support the pavement
- It provides a frost barrier to help reduce winter damage due to freezing and thawing.
Much depends, when designing a sub-base for your driveway, on the particular soil conditions at your site. In some areas, a well-drained, sandy soil can act as its own sub-base without modification. In other areas, where clay soils or other poorly compacted soils exist, a brand new sub-base must be laid. Where there is an existing driveway, a poorly designed or contaminated sub-base may have to be completely removed and replaced. No single solution will work in every case.
The main issues that need to be addressed when preparing the base for paving are; the sub-grade, drainage, base thickness, base stability, dimensions and compaction. The minimum thickness of the sub-base should typically be 4 inches. The thickness of the base will be determined by what the driveway will be used for. If it’s a typical driveway and normal sized cars or SUV’s will be driving on it, 4-6 inches of base is adequate. For heavy equipment, trailers or trucks, and in some special situations, a deeper base is recommended.
A properly compacted base is crucial. The best type of base is class 5 limestone or recycled class 5 made out of concrete bituminous (con-bit). These bases are highly compactable and strong. A vibratory drum roller should be used versus a static roller to compact the base. It will create the greatest compaction density because the vibrating action of the roller will cause the base material to be compacted from the bottom up. A vibratory plate compactor will be used in areas not accessible by the rollers.
The surface of the compacted base should be smooth, with a maximum tolerance of plus or minus 3/8 inch over a 10 ft straight edge. And finally, the base must be firm and ready before paving. On occasion, especially if the base is 6 inches or more, additional time may be needed to let the base firm up.