The production of roadbase involves taking a range of various aggregate sizes, made available during the crushing process, and recombining them into a balanced formula that produces the required properties specific to a given application. The finished product must meet the specified requirements of Queensland Transport and Main Roads for grading, workability, placeability, strength, density, long-term durability and appearance. This ensures repeatable and reproducible measurable engineering properties can be achieved in the final product.
A non-spec roadbase is a gravel blend that has similar characteristics to the standard roadbase products, however they are not certified to the standard.
Moisture and Compaction
The quantity of moisture within a specific roadbase blend is critical to enable the particles to come together, during placement and compaction, in a manner that allows as much air as possible to be removed and only aggregate particles left to fill the voids within the rock skeleton. This will ensure that even distribution of all the particles throughout the mix, has occurred even after compaction has taken place. Too little water within the roadbase during placement and compaction can have the effect of allowing particles to segregate or be broken down and thus in situations density will not be able to be obtained. Too much moisture and the overwork required to dry back can further breakdown aggregate particles and lead to segregation affecting the ability to obtain proper compaction within that roadbase layer. Improper compaction can lead to a multitude of issues and ultimately pavement failure in a shorter time than allowed for in the design. One of the main issues arising from under compaction of road base layers will be rutting of the surface. This is due to the movement of particle during cycles of wetting and drying during the life of the pavement.
When building up a base to the required height it is critical to not make each lift or layer too deep. The maximum depth of each lift should be dictated by the quality of the compaction. The bigger the roller or compactor the deeper the lift you can achieve. If you are using a jumping jack or vibrating plate compactor you will need to keep your lifts quite shallow. After spreading each layer you must make sure you have satisfactory moisture and compaction before you spread the next layer.