Polymer Modified Bitumens

Both the chemical nature and the concentration of polymeric modifiers in polymer-modified bitumens can be determined by DSC. The aging behavior of bitumen and polymer-modified bitumen in road asphalt or of bitumen extracted from road asphalt, may be analyzed and characterized by thermoanalytical methods. Thermogravimetry in inert gas has shown, for example, that the concentration of evaporable components decreases as a consequence of aging whereas the coke residue (residue at 600 °C or 800 °C oven temperature) increases, and that is connected with an increase in the concentration of asphaltenes. 

FM 4470, Single-Ply, Polymer-Modified Bitumen Sheet, Built-Up Roof (BUR) and Liquid Applied Roof Assemblies for use in Class 1 and Noncombustible Roof Deck Construction, 2012. 

According to CEN EN 13808 (2013), a combination of letters and numbers is used to describe a bitumen emulsion. The cationic emulsions are designated by the letter C two numbers indicating the nominal binder content one or up to three letters such as B (for paving grade bitumen), P (for polymer-modified bitumen) and F (for bitumen with more than 3% [m/m] flux oil) and a number indicating the class of breaking behaviour. 

It is noted that the CEN EN 13808 (2013) standard applies to emulsions of paving bitumen, fluxed bitumen or cut-back bitumen and to emulsions of polymer-modified bitumen, polymer-modified fluxed bitumen or polymer-modified cut-back bitumen, which also includes latex-modified bituminous emulsions. 

The test is suitable for all bituminous binders for surface dressings, such as conventional or polymer-modified bitumen, cut-back bitumens, fluxed bitumen or bituminous emulsions with conventional or modified bitumen. 

Permanent deformation behaviour can also be determined by using the triaxial cyclic compression test (see Section 7.6.2). Figure 3.13 shows results obtained when asphalt concrete mixtures were used (AC 20 mm) with and without polymer-modified bitumen. 

However, it does not improve the elastic behaviour of the asphalt (bituminous mixture). Thus, asphalts with thermoplastic polymer-modified bitumen present good resistance to deformation at high ambient temperatures, but generally their fatigue cracking resistance is similar to or even less than that of asphalts with unmodified bitumen. 

In an evaluation study on asphalts with modified bitumens, it was found that asphalt layers with thermoplastic polymer-modified bitumen, when laid over cracked and uncracked surfaces, have more intensive cracking within a very short period, in contrast to the asphalt layers where elastomer-modified bitumen was used (Anderson et al. 1999). 

Because of the abovementioned properties and results, the use of thermoplastic polymer-modified bitumen is recommended in areas with high ambient temperatures where the asphalt layers are subjected to high traffic loads but not over cracked pavement surfaces. 

Regarding the asphalt s characteristic Marshall properties, the use of thermoplastic polymer-modified bitumen increases stability and decreases when compared to the same asphalt with the same binder content. 

The asphalts produced with thermosetting polymer-modified bitumen have excellent adhesive ability, excellent resistance to deformation, excellent fatigue performance and high stiffness modulus. 

In some countries, such as the United Kingdom, for high-quality surface dressings with calcined bauxite chippings, the thermosetting polymer-modified bitumen is the only binder recommended to be used. 

Experimental measurements carried out in 2009-2011 on the use of multigrade bitumens in chip sealing (surface dressing) did not show any advantage for multigrade bitumens compared to standard binders with a similar 25°C penetration value (Herrington et al. 2011). Multigrade bitumens do not replace polymer-modified bitumens. 

To ensure construction quality and since there is a great variety of polymer-modified bitumens in the market, the properties of the polymer-modified bitumen must be specified precisely to satisfy the needs. 

In the European Union, the grades of polymer-modified bitumens are selected/specified in accordance with CEN EN 14023 (2010). 

The properties specified for all polymer-modified bitumens ensure (a) consistency at intermediate service temperatures (with reference to penetration at 25°C), (b) consistency at elevated service temperatures (with reference to softening point), (c) cohesion (with respect to force ductility, tensile test or Vialit pendulum), (d) resistance to hardening, (e) brittleness at low service temperature (with respect to Eraass breaking point) and (f) stain recovery (with respect to elastic recovery). 

The framework specifications for polymer-modified bitumens by CEN EN 14023 (2010) are given in Tables 3.18 through 3.20. 

The properties in Table 3.18 shall be specified for all polymer-modified bitumens and are considered essential properties. The properties in Table 3.19 are required so as to meet specific regional conditions and are characterised as special for regional requirements. The properties in Table 3.20 are additional properties they are non-mandated but have been found useful to describe better the polymer-modified bitumens. 

For instance, a polymer-modified bitumen (pmb) designated as 25/55-70 is a bitumen with penetration varying from 25 to 55 dmm, which belongs to class 3 of Table 3.18, and with a softening point 7°C, belonging to class 4. The rest of the essential, special and additional properties are chosen in such a way that the modified bitumen can satisfy the project and regional requirements (traffic volume, ambient temperature, etc.). 

Undoubtedly, the engineer has the freedom to choose/specify any combination of properties for the modified bitumen that will be used. This introduces a problem to the producers since they have to use different recopies and provide different storage facilities per grade requested. After many years of experience in pavement construction projects, the author proposes three representative grades of polymer-modified bitumens (elastomer modified)... 

Table 3.18 Framework specifications for polymer-modified bitumens - properties that apply to all polymer-modified bitumens... 

Sources Reproduced from CEN EN 14023, bitumen and bituminous binders - Framework specification for polymer modified bitumens, Brussels CEN, 2010 and from CEN EN 13808, Bitumen and bituminous binders - Framework for specifying cationic bituminous emulsions, Brussels CEN, 2013. With permission ( CEN). 

The main test is the RTFOT at 163 C. For some highly viscous polymer-modified bitumens where the viscosity is too high to provide a moving film, it is not possible to carry out the RJFOT at the reference temperature of 163°C. In such cases, the procedure shall be carried out at 180°C in accordance with CEN EN 12607-1. 

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