Hot Rolled Asphalt (HRA) is a dense mixture of coarse aggregate, sand, mineral filler and bitumen. This material has a high proportion of fine aggregate in the mix and subsequently has a low percentage of air voids when compacted. The rich mortar of bitumen and fines in the this material provides it's mechanical properties. Consequently, HRA is a very durable material which has a high resistance to fatigue cracking.
HRA is a dense mix with a low percentage of air voids when compacted. The most common mix types for road construction are 30% 0/14mm and 35% 0/14mm HRA. In order to attain macro texture on the finished road surface 20mm high PSV pre-coated chips are rolled into the surface during the laying of these HRA materials. The rate of spread of the high PSV chips is calibrated in order to achieve the required texture depth which is normally ≥ 1.5mm. Other types of HRA commonly used are 55% 0/10mm, 55% 0/14mm and 0/3mm sand asphalt. 55% HRA is normally used when a durable hard weraing surface is required and there are no macro texture requirements i.e. carparks, industrial estates etc. 0/3mmm sand asphalt is used on bridge decks as a protective layer over waterproofing in the event of future excavation.For major road construction projects a HRA mix is designed to determine the optimum mix constituents and performance. The Marshall method of mix design is used to determine the optimum binder content at the selected mix grading. For performance mix types the resistance to permanent deformation may also be specified.