Cut-back and fluxed bituminous binders

Cut-back bitumen constitutes bitumen whose viscosity has been reduced by the addition of a relatively volatile flux. In case the volatile flux is derived from petroleum, the material is called petroleum cut-back bitumen. Typical petroleum-derived fluxes used are white spirit and kerosene. Petroleum cut-back bitumens are almost exclusively used, and, for simplicity, they are called cut-back bitumens (or asphalts). 

When the viscosity of the bitumen is reduced by the addition of a flux oil (a relatively involatile oil), the bitumen is called fluxed bitumen. Flux oils can be derived from petrochemical, carbochemical or petroleum origin materials, or a mixture of these materials. In this case, the product is called petroleum fluxed bitumen or mineral fluxed bitumen. Typical flux oil is the gas oil of various boiling ranges. 

Additionally, flux oils can be derived from plant-based (vegetal) products. In this case, the product is called vegetal fluxed bitumen. 

The viscosity of the bitumen is significantly reduced that cut-back bitumens or fluxed bitumens are considered as liquids and require far less heating energy during application in comparison to solid (at ambient temperatures) bitumen. 

Cut-back and fluxed bituminous binders are suitable for use in the construction and maintenance of roads, airfields and other paved areas. The bitumen used may be paving grade bitumen (in most cases) or by addition of polymer. 

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The recommended classes of cut-backs and fluxed bituminous binders with the technical requirements specified by CEN EN 15322 (2013) are as shown in Table 3.9. 

Table 3.9 Specification framework for technical requirements and performance classes of cut back and fluxed bituminous binders... 

The cohesion of stabilised binder from polymer-modified cut-back and fluxed bituminous binders, which are used for surface dressings, shall be determined in accordance with CEN EN 13588 (2008). For binders used in asphalt mixes, the test methods given in either CEN EN 13587 (2010) or CEN EN 13589 (2008) rosy be used. For binders used in other applications,any one of the three methods listed above, CEN EN 13587 (2010), CEN EN 13589 (2008) or CEN EN 13588 (2008), msy be used. 

This rotating spindle viscometer is used for the determination of dynamic viscosity of a variety of bituminous binders modified and unmodified bituminous binders, bituminous emulsions, cut-back and fluxed bituminous binders by means of rotating spindle (coaxial viscometer) viscometer, at typical test conditions (temperatures and rate of shear). 

The typical test temperature for bituminous emulsions is 40°C, and for cut-back and fluxed bituminous binders, it is 60°C. However, other temperatures may also be used, such as 90°C for cut-back and fluxed bituminous binders. 

Similarly, for cut-back and fluxed bituminous binders to break possible storage-induced thixotropy effects, the spindle rotates initially at a speed such that a shear rate of 50 5 s" is achieved and is then left for 60 5 s. After this period, the spindle is set to rotate at a speed such that the shear rate of 2 s" is achieved. Readings are taken, as for bitumen emulsions, after the shear rate is stabilised for a period of 30 3 s. 

There are various types of efflux or cup viscometers, two of which are shown in Table 4.1. The standard tar viscometer type (STV), also called efflux viscometer, is recommended to be used for bituminous emulsions (CEN EN 12846-1 2011) or for cut-back and fluxed bituminous binders (CEN EN 12846-2 2011). An efflux viscometer (STV) is shown in Figure 4.6. 

Flowever, for cut-backs and fluxed bituminous binders, the flash point is usually determined by the Pensky-Martens closed-cup apparatus (ISO 2719 2002 or ASTM D 93 2013), by the tag open-cup apparatus (AASHTO T 79 2012 ASTM D 3143 2008) or by the Abel closed-cup apparatus (CEN EN ISO 13736 2013). 

When the Pensky-Martens apparatus is used, the expected flash point of cut-backs and fluxed bituminous binders should be >60°C when the tag open-cup apparatus is used, the expected flash point may vary from >38°C to >66°C and when the Abel closed-cup apparatus is used, the flash point may vary from 23°C or less to >45°C. 

CEN EN 13074-1.2011. Bitumen and bituminous binders - Recovery of binder from bituminous emulsion or cut-back or fluxed bituminous binders - Part 1 Recovery by evaporation. Brussels CEN. 

Source Reproduced from CEN EN 15322, Bitumen and bituminous binders - Framework for specifying cut-back and fluxed... 

The test method is applicable to bitumen, modified binders and bituminous mastics (homogenous mixture of filler and bituminous binder) and stabilised (recovered) bitumen from bituminous emulsions, cut-back or fluxed bitumen. 

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