Black curves and creep behaviour of crumb rubber modified binders containing warm mix asphalt additives

Warm mix asphalt (WMA) is a new research topic in the field of road pavement materials. This technology allows lower energy consumption and greenhouse gas (GHG) emissions by reducing compaction and placement temperatures of the asphalt mixtures. However, this technology is still under study, and the influence of the WMA additives has yet to be investigated thoroughly and clearly identified, especially in the case of crumb rubber modified (CRM) binders. In order to study the effect that different types and quantities of organic waxes have on the high and intermediate temperature properties of 15 % and 20 % CRM binders, a dynamic shear rheometer (DSR) was used. Using Black diagrams, the rheological behaviour of the binders for the defined range of test temperature and frequency are summarised in a single diagram. In this way, a preliminary evaluation of the rheological behaviour in the extended domain of time and temperature can be attained as well as the effectiveness of the time-temperature superposition principle (TTSP) on the materials under study. Creep tests were also performed in order to evaluate the differences regarding mechanical response due to the addition of rubber and WMA additives, and particularly the ability to recover the strain at high temperatures. The results of this study reveal that these binders do not conform to the Time Temperature Superposition Principle (TTSP) and their rheological behaviour is strongly affected by the interaction of waxes and bituminous matrix and thus generally exhibited a higher elasticity compared to the corresponding control binder. The creep test results carried out proved the enhancement of elasticity and the resistance to permanent deformation produced by the addition of waxes. The WMA additives significantly lower the maximum deformation when compared to the control binders and slightly increased their elastic recovery.