Open graded asphalt is produced from crushed or partly crushed aggregate containing hardly any fine material and incredibly little for filler injections. It is bound together with a relatively small amount associated with bitumen, is dependent mainly on mechanized lock with regard to stability and it has a high voids content. Because of its porosity it is less long lasting than a dense graded mix. Typical blend properties tend to be shown in beneath.
By Weight %:
Coarse Aggregate = 75
Fine Aggregate = 20
Filler = 1
Bitumen = 4.0 ~ 6.0
By Volume %
Coarse Aggregate = 56.3
Fine Aggregate = 14.6
Filler = 0.7
Bitumen = 8.4
Air Voids = 20.0
The open texture offers enhanced skid resistance and that’s why the mix is mainly utilized as a friction course. The porous mix of open graded asphalt enables water to escape through beneath vehicle tyres as well as as a result offers improved moist weather skid resistance from higher rates of speed. See notes