# Bitumen and Bitumen Modification: A Review on Latest Advances
## 4 PmBs in Warm Mix Asphalt (WMA) Technology  
A new kind of polymer-modified bitumen technology has been introduced in recent years. It combines the classic ones (PmB) with the warm mix asphalt technique (WMA). One of the methodologies employed to shift from hot mix asphalts to warm ones is based on the use of waves. This is due to the fact that above their melting temperature, they act as plasticizers, while at low temperatures they crystallize and act as fillers [4; 219; 220]. While the PmB is well consolidated the WMA is relatively new, but rapidly growing, due to its economic and environmental advantages. Compared with classic hot mix asphalts (HMA), warm mix ones, in general, are characterized by lower fuel consumption and costs, lower production of greenhouse gases, fumes, and odors, which improve the environmental impact and working conditions, extension of haul distances, and good workability during laying and compaction [219]. Although naturally present as constitutive components of all crude oil products [221; 222] and studied in the technical literature, where bitumen wax content [223; 224; 225], crystallization properties [226], chemical structure [227; 228], and influences on bitumen and bitumen mixture properties [220; 223; 224; 225; 226; 227; 228; 229; 230; 231; 232; 233; 234] were analyzed, waxes affect the binder performances. For example, wax melting can soften bitumen at high service temperature, reducing rutting resistance of the pavement, while at low temperatures wax crystallization can increase stiffness and sensitivity to fatigue and thermal cracking [223; 234; 219]. Nowadays there is an increase development about warm polymer modified bitumen which can maintain the advantages of both technologies (WMA and PMB) although this is not an easy task because waxes used as warm modifiers reduce the high temperature viscosity while increasing the low temperature stiffness and polymers do basically the contrary [219]; simply adding the two modifiers does not guarantee the enhancement of bitumen properties like those obtained by adding single ones. For example, a ternary mixture bitumen/polymer/wax has significantly different properties (like viscoelasticity) from those predictable by superposing the effect of wax and polymer only and the final warm effect and performances of the binder will be determined by the interactions between the three components. Scientific studies on this ternary mixture are still limited. [PERSON] et al. [235] for example, studied the addition of paraffinic waves to a polymer-modified mastic bitumen, showing that a 4% wax addition improves workability of the mastic bitumen without affecting its performances. [PERSON] et al. [236; 237] studied the artificial long- and short-term aging of a PmB mixed with wax additives. Other studies analyzed the properties and pavement performance, compacting temperatures, long-term performance [238], fatigue characteristics [4], thermo-mechanical properties [239], and viscosity and rheological properties [240]. [PERSON] et al. [219] conducted a preliminary investigation by mixing bitumen, SBS, and three typologies of wax chosen among the three categories: paraffinic (obtained by Fischer-Tropsch process), partially oxidized and maleic anhydride functionalized. By morphological and calorimetric analyses and solubility tests they were able to characterize blend behavior related to wax type. In particular, they found that paraffinic waves preferentially reside in the polymer-rich phase and slightly enhance the bitumen polymer compatibility. Partial oxidation tends to aggregate with the asphaltene rich phase reducing compatibility with the polymer, while functionalized wax, although not clear where they are located, has a considerable compatibilizing effect strongly altering the colloidal equilibrium of the bitumen polymer blend.