The distilled bitumen, used in membrane manufacturing, is also called "road Bitumen" or "road asphalt", since it is the same product, coming from the bottom of the crude oil distillation, which is used in road paving. It is transported as hot liquid, so it's important to check the supply distance, and the required time for transportation. Generally it is available in two main grades (Refer to ASTM D5 standard): the harder one (around 60 - 90 dmm) and the softer one (around 160 - 200 dmm). Anyway, selection of these grades, or different ones, can be made after evaluation of climate conditions, market uses, and final destination of the membranes.
The filler is used mainly to reduce the compound cost, and partially to increase the mechanical resistance of the compound itself. It can be used in percentages from 5 to 55 %, depending on the value of the compound and the techincal features of the finished product: but in any case it is very important make a proper filler selection, base on granulometry, physical properties (e.g. "oil absorption"), and chemical reactivity (e.g. very alkaline behaviour), and of course, most important, the practical properties it gives to the compound. In the world, it is very used calcium carbonate with a granulometry ranging from 10 to 50 microns, due to the fact it has a low density and does not influence viscosity of the compound. Limestone is the natural CaCO3 (Calcium carbonate). In Italy we extract it from marble cutting.
The main polymers used to modify the bitumen are of these two families:
The first group (Polyolephines) includes APP (Atactic Polypropylene), IPP (Isotactic polypropylene), PE (Polyethylene), APAO (Atactic polyalphaolephines), and related variations (e.g. different grades of PE, catalloy polypropylenes, etc.). The bitumen modification with these polymers gives compounds with an excellent heat resistance, plasticity, and good cold flexibility. The second group (SBS) includes Styrene - Butadiene - Styrene polymers, possibly modified with other polymers. The bitumen modification with these polymers gives compounds with an excellent elasticity, good heat resistance, and excellent cold flexibility. There are no real technical reasons to prefer one compound rather than the other. In any case, our plants are capable to produce membranes with both compounds