THE FUNDAMENTALS OF RECYCLING BITUMINOUS MATERIALS

I do not wish to insult anybody, but a lot of people have not understood the basic principles of recycling bituminous materials.
A bituminous material is thermoplastic, meaning, when it is hot it is able to be worked, when it is cold it is solid, well, for practical purposes.  
A bituminous mixture used for conventional road surfacing consists mainly of aggregate and bitumen.
It is unlikely that if these two components where of good quality at the time of laying that they will have degraded much during the life of the pavement layer that they were contained in.
The surface course will have deteriorated most but only at the surface where the bitumen will have undergone some oxidisation, but material in the matrix of an impervious layer will be substantially the same in physical properties as at the time it was laid.
Note the previous sentence carefully because it is a fact that the most change in the physical properties of a bitumen binder will occur during the mixing process and the time of hot storage prior to laying, but temperatures of bituminous materials is another subject.
So, let me be even more blunt with the scenario, if you take two freshly, and correctly mixed batches of asphalt, and you leave one in the insulated lorry and you tip the other batch on a clean hard standing and deliberately "pull it out" so that it loses heat.

So, what will be the difference between the two batches in an hour ?
One will be hot and still in a plastic condition and able to be laid, the other will be cold and unable to be worked, and unfortunately this situation too often arrives when laying small tonnages. 
But other than this difference in temperature the two batches will be the same product.

But if you were able to reheat the cold material in a controlled procedure, so that it was heated through but not overheated, that bituminous material would be practically as good as new.

Note :- With correctly produced hot remixing you will have a complete break down and remixing of the individual constituent aggregate particles, this will not be the case with foam mixed recycling of reclaimed bituminous materials.
E.g. you could not take pieces of reclaimed bituminous surfacing, as shown in the picture above, and produce a foamed bitumen product without first crushing the reclaimed material to an appropriate size range.  

If you have the services of a good Materials Engineer/Technician who knows the properties of the bituminous materials available for recycling the principles of this process has got to provide opportunities of a financial advantage in a number of situations as well as being environmentally friendly.

NEW - However in re-heating / re-mixing an existing bituminous material you MUST have a reasonable assumption of what the original material was/is, i.e. is the bituminous mixture for recycling a hot rolled asphalt (HRA) with a stiff 50pen binder that can be reheated to a 160/180 degrees centigrade with little damage or hardening to the binder and associated fume production, OR was/is the material a bituminous mixture with a "soft", low viscosity binder, that must have a lower temperature mixing procedure to avoid damage to the binder, and prevent fume production as the volatile oils are driven off by overheating.
Of course it follows that a "softer" material will cost you less to recycle as it needs less heat to attain its workable temperature, but it would be unwise to recycle a stockpiled "soft" material on to a high stressed site.
I have already included a link to the temperatures of bituminous materials  but may I also suggest you take a look at bitumen viscosities for bituminous materials  because all the rules that apply to the production of new bituminous mixtures apply equally importantly to recycled product.
If you are working with bituminous materials you need to understand bituminous materials, that is why I keep saying, "consult your Materials Engineer", he is there to help prevent you making mistakes and show you the best way of working with the material you have to recycle, not to be an obstruction.

Finally, I really do believe where at all possible bituminous materials should be reprocessed as bituminous materials because that is where the term "adding ＆#118alue" can really mean what it says.

I hope you find the information and references presented below are helpful to you, but I stress you need "materials" guidance with this process especially when you are recycling materials that are not of a known and consistent source.