The specifications proposed by the Strategic Highway Research Program (SHRP) are based essentially on the complex modulus, and it is therefore interesting to translate them into terms of ring and ball softening temperature (RBT) to compare them to other national specifications, in particular French specifications. Given the temperature limits fixed by the SHRP to obtain: (1) a modulus corresponding to the reciprocal of the loss compliance (1/J") before and after the Rolling Thin film Over ageing Test (RTFOT); (2) a loss modulus (G") and a modulus corresponding to the reciprocal of the creep function (S) after the PAV (Pressure Ageing Vessel) process; and assuming that: (1) the reciprocal of the loss compliance (1/J"), the loss modulus (G"), and the norm of the modulus G* are not very different under these conditions of temperature and pulsation (10 rad.s-1); and (2) the penetration index is between -1 and 1; it is possible to use Van der Poel's nomograph to calculate: (1) the ring and ball softening temperatures corresponding to the limits of the classes; (2) the minimum allowed increase of the softening temperature corresponding to the evolution during coating simulated by the RTFOT (to avoid rutting); and (3) the maximum allowed increase of the softening temperature corresponding to the evolution in situ simulated by the PAV (to avoid the various forms of cracking). Since the calculation assumptions are realistic, at least for French bitumens of the 35/50 and 50/70 classes, it follows that the specifications proposed by the SHRP are more stringent than those in force in France. Furthermore, they are also more complete,since they are used simultaneously for pure bitumens and polymer-modified bitumens, with allowance for ageing in situ by the PAV test and cracking at temperatures far below 0 C. (A)
Abstract