# Bitumen and Bitumen Modification: A Review on Latest Advances
## 2. Bitumen Polymers
### Thermoplastics Polymers  
Polyolefinic plastomers, also known as thermoplastics, whose category includes: Polyethylene (PE), polypropylene (PP), ethylene vinyl acetate (EVA), ethylene butyl acrylate (EBA), and polyvinyl chloride (PVC). Polyethylene which can be found in in three forms; low-density polyethylene (LDPE), high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE) are the most common plastomers. The use of plastomers as polymers to obtain PmBs arose as a consequence of the high costs of the sytrenic polymers and the degradation phenomena due to their unsaturations. On the contrary, polyolefinic plastomers have a low cost and high availability presenting also higher stability than sytrenic ones. Polyolefin polymers addition generally increases the bitumen stiffness and a good rutting resistance [53; 54]. For these reasons plastomers play a leading role in PmBs in which they represent about 15% of the reference market. Reclaimed polyethylene is recovered from low-density domestic waste PE carry bags. [PERSON] and [PERSON] investigated an 80/100 paving-grade bitumen with different PE ratios [55]. The blends were tested using Hamburg wheel track tests, resilient modulus tests, an indirect tensile test, and an unconfined dynamic creep test. The results analysis showed that the PE-modified asphalt mixtures exhibited better performance characteristics than conventional mixtures. Even though polyethylene and polypropylene are the most common plastomers used, their non-polar nature results in compatibility problems with bitumen also sharpened by their tendency to crystallize which deeply restricts the interaction with bitumen [56; 4]. In addition to compatibility problems of thermoplastics, these kinds of polymers also failed to increase the bitumen elasticity [53]. In an attempt to avoid the problems of compatibility and crystallization, other kinds of thermoplastics have been introduced. Principally, these modified polymers are obtained by inserting acetate groups, producing ethylene vinyl acetate (EVA) with vinyl acetate group content higher than 14%, ethylene methyl \begin{table}
\begin{tabular}{c c} \hline \hline  & Polyethylene (PE) \\  & Polypropylene (PP) \\
**Theroplastics Polymers (see Section 2.1)** & Ethylene-Vinyl-Acetate (EVA) \\  & PVC \\  & EBA \\ \hline
**Theroplastic Elastomers (see Section 2.2)** & Styrene-Butadiene-Styrene-Block copolymers (SBS) \\  & Styrene-Isoprene-Styrene-Block copolymers (SIS) \\ \hline  & Epoxy resin \\
**Thermosets (see Section 2.3)** & Polyurethane resin \\  & Acrylic resin \\  & Phenolic resin \\ \hline  & Styrene-Butadiene rubber (SBR) \\
**Natural and Synthetic Rubbers (see Section 2.4)** & Natural rubber \\  & Polyolidefins \\  & Reclaimed Tire rubber \\ \hline  & Sulphur (S) \\
**Bitumen Chemical Modifier (see Section 3)** & Polyphosphoric acid (PPA) \\  & Reactive Polymers \\  & Maleic Anhydride (MAH) \\  & Nanocomposite Modifiers \\ \hline
**Warm Mix Asphalt methodology (see Section 4)** & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Different categories of polymers mainly used in bitumen modification. acrylate (EMA), and ethylene butyl acrylate (EBA). Esters groups of these polymers have the double advantage of increasing the polarity and reducing their crystallization tendency, disrupting the closely packed crystalline microstructure [50]. Both factors increase the bitumen compatibility and storage stability of the blend. In general, relative to the compatibility of plastomers with the bituminous matrix, it is believed that the higher the ester fraction is, a lower crystallinity is achieved. However, the crystallinity degree must be carefully balanced. If the crystallinity degree is to low, the lattice formed tends to be disrupted early after the crystals are interlocked with the bituminous fraction. In the EVA case, the optimal crystallinity degree is obtained using vinyl-acetate percentage ranging from 14% to 28%.