Hot rolled asphalt

HRA was developed in the United Kingdom aiming to produce a more economic and workable asphalt than MA, which was widely used until then. The incorporation of coarse aggregates in the mixture slightly increased the stiffness of the mixture. As a consequence, there was no need to use hard bitumen, such as in the case of M A. Furthermore, with the addition of coarse aggregates, the volume of the mixture increased and at the same time workability was improved. 

The key feature of this mixture is that the aggregate particle size distribution curve presents a discontinuity between certain sieves. For this reason, FIRA is also known as gap-graded mixture. 

Generally, the HRA is a dense, gap-graded asphalt, in which the mortar of fine aggregate, filler and high viscosity binder are the main contributors to the performance of the laid material and its stiffness. 

HRA requires relatively higher compaction energy than AC. 

The use of high-viscosity bitumen results in higher temperatures at compaction, which often are difficult to maintain, particularly during winter months. The production cost of HRA, owing to high binder content, is higher than that of AC. 

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BS 594, Part 1 Hot rolled asphalt for roads and other paved areas — Specification for constituent materials and asphalt mixtures , 1992. 

Max.AAV for chippings for hot rolled asphalt and surface dressing, and for aggregate in slurry and microsurfacing systems... 

Some countries, such as the United States, England, Germany and France, pioneers in invention and production of asphalts, for many years now, have developed asphalts that are used worldwide. These mixtures were asphalt concrete (AC), macadam, hot rolled asphalt (HRA), mastic asphalt (MA) and gussasphalt. 

Source Reproduced from CEN EN i 3 i 08-4, Bituminous mixtures - Material specifications - Part 4 Hot Rolled Asphalt, Brusseis CEN, 2008. With permission ( CEN). 

Nicholls J.C. 1998. Specification Trials of High-Performance Hot Rolled Asphalt Wearing Courses. TRL Report 315. Crowthorne, UK Transport Research Laboratory. 

All stiffness test methods are considered equivalent and are recommended to be used (CEN EN 13108-20 2008) in specifying asphalt concrete and hot rolled asphalt in terms of fundamental, performance-based properties. 

Tables 7.6 through 7.8 give the limiting wheel-tracking values recommended to be used in the United Kingdom to determine the target composition of asphalt concrete, hot rolled asphalt and SMA mixtures.

Table 7.7 Limiting wheel-tracking test requirements for hot rolled asphalt...

Another nomograph was developed by Cooper and Pell (1974) referring to dense-graded macadams and hot rolled asphalts. The nomograph is expressed by the following mathematical equation ... 

The minimum rolling time depends on the type of material. The minimum rolling time for asphalt concretes and porous asphalts is 20 min, whereas the minimum rolling time for stone mastic asphalt, hot rolled asphalt and mastic asphalt is 30 min. In the case of coated chippings, the minimum rolling time is 10 min. 

As for the top upper layer (surfacing), the recommended material is asphalt concrete for very thin layers. Other asphalts, such as porous asphalt (PA) and hot rolled asphalt (HRA) with coated chippings, may also be used in new pavements. 

The pavement surface condition is assessed in terms of riding quality, rut depth, texture depth and surface cracking, and, if hot rolled asphalt surfacing, fretting. 

Adding enough molten sulfur to hot aggregate—asphalt mix increases its fluidity and produces a mix which can be molded or shaped. Casting these mixes requires little or no consolidation effort, and, specifically with pavements, rolling is not required. It has been demonstrated by micro-... 

AASHTO PP 3.1994. Provisional standard for hot mix asphalt (HMA) specimens by means of rolling wheel compactor. Washington, DC American Association of State Highway and Transportation Officials. (1996), last printed in 2002. 

Rolling rig machines The rolling rig machine rotates the cleaned and primed pipe on mechanically driven dollies , while a tank travelling alongside the pipe floods it with hot asphalt or coal-tar-base enamel. 

Where moisture (or air) in the substrate is so extensive that it appears impossible to eliminate it, or where it is fed from a subsurface source, a satisfactory membrane can sometimes be attained by ignoring the blisters in the first thin layer of hot asphalt, and then laying over this layer a 6 to 12 mil thick pinhole-free, plasticized PVC sheet, lapping all edges 2" or more, and rolling out all wrinkles and air bubbles, then laying another Vs" thick layer of hot asphalt on top of it. The use of visqueen and other stiffer plastic sheets yields mixed results due to poor bond to both asphalt and mortar, and the difficulty of working out air pockets and wrinkles. 

The standard rolling thin him oven test (RTFOT) (ASTM D-2872) is used to simulate the short-term aging of the binders during the hot-mixing process and has the purpose of determining the hardening effect of heat and air on a static him of asphalt when exposed in a thin him. The procedure utilizes a moving him exposed for 75 min at 163°C (325°F). 

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