The acidity of bitumens is an important factor, resulting from the origin of the crudes from which they are made and the refining means used. Naphthenic bitumens, with marked natural acidity and appreciated for certain emulsion applications, are gradually being replaced by paraffinic bitumens whose acidity must be measured and sometimes corrected by addition. In this case, the laboratory must have efficient and reliable methods to control this parameter.

The acid number of a bitumen is the amount of potassium hydroxide (mg KOH) that must be added to 1 g of bitumen to neutralize the free acid constituents. The test consists of following the variations in the electrical potential (mV) of a non-aqueous bitumen solution following the addition of known doses of titrating solution (KOH). The equivalence point is reached when the volume of titrating solution added has neutralized the acidic constituents of the test sample. This potentiometric method presents better precision data than the colorimetric method described in the documentation FD T66-013 (2016).

NF T66-066 | XP CEN/TS 17482