Evaluation of bitumens consistence modified by polymers at equipenetrating temperature

Abstract

At present the penetration (Р25) and the softening point (ТR B) remain the main quality characteristic of both bitumens and PMBs. The penetration has more informative valeu than ТR B. The reason for this is that Р25 is actually a shear strength property of bituminous cements while dipping the indenter (penetration needle) into them under the effect of stable load. However, the softening point is valuable only for the bitumens with a low penetration index but useless in respect of the bitumens which are modified by more than 2,5-3,0 % of the SBS-type polymer. A clear proof of this are the valeus of stability determed during storage, when a system is formed in the upper part of the tube in which the polymer is the medium and the phase is the bitumen. Such a system is characterized by high penetration and immensely high ТR B. According to designers idea the softening point temperature is informative when the 800×0,1 mm penetration is correspondant. This rule which underlies the ring-and-ball test (R B) can not be applied to the the РМВ. Moreover, long ago I. Ph. Pfeiffer and P. M. Doormal prefered to use Т800 for specifying the penetration index of bitumens, which subsequently transformed into ТR B because of the proximity of the values of the softening point temperature and Т800 for the "sol-type" bitumen. As for the РМВ the substitution results in dangerous errors while forecasting on the basis of ТR B rut resistance of asphalt-concretes. In accordance with W. Heukelom viewing the softening point temperature in a historic retrospective as the equipenetrating temperature will allow to enhance the reliability of the РМВ consistence evaluation at high summer temperatures, to simplify the testing process by means of the traditional and durable penetrometer will be by using a prolonged needle to 120 mm.